MDOT Policy Manual - User contributions [en]

Bridge: Length/Span Configuration

2016-12-07T20:01:03Z

LLBarry: /* Environmental Impacts */

{| class="wikitable"
|-
| colspan="3" |
'''Length/Span Configuration'''

|-
| colspan="3" |
=Primary Guidance=
*Provide a span configuration to accommodate the needs under the bridge while minimizing the height of supporting abutments
*Provide a minimum bridge horizontal under clearance so that the bridge is not classified as [http://tinyurl.com/otkjvhf| Functionally Obsolete]
*The lane, shoulder, and sidewalk widths under a bridge should be consistent with the roadway configuration beyond the bridge
*Provide a span configuration that provides the most cost effective structure
*Consider future capacity roadway or other facility (i.e. railroad, trail, etc.) improvements under a bridge and the timeframe for when those improvements are planned when determining the bridge length
*Where possible, eliminate drainage ditches and safety grading under a bridge and replace them with a concrete barrier supporting the fill slope to reduce bridge lengths
*When environmental entities request lengthening bridges to avoid environmental impacts, evaluate the benefits of avoiding the environmental feature compared to the cost of constructing and maintaining a longer bridge

|-
| colspan="3" |

=Discussion=

==General==
Bridge lengths shall be sufficient to span over the roadway or facility being crossed. Longer bridges with short abutments are preferred since they create an open structure while providing added safety in the ability to see beyond the bridge. Although this results in a bridge that is longer than it would need to be with full height abutments, the tall abutments and foundations costs generally offset the longer superstructure costs. Tall abutments, especially those located adjacent to a paved roadway, can also be visual obstructions and require additional impact damage protection. Shorter abutments make inspections easier, and the additional length provided under the bridge could be used to accommodate future widening, if needed.

==Functionally Obsolete==
All bridges are rated for [http://tinyurl.com/otkjvhf| functional criteria] to determine if a bridge is classified as [http://tinyurl.com/otkjvhf| Functionally Obsolete]. This includes horizontal under clearance, which evaluates clearance from the bridge substructure unit to the through roadway. The required minimum horizontal under clearance is based on the roadway type. A rating value from 0 to 9 is assigned with any rating below a 4, resulting in the bridge being classified as Functionally Obsolete. In order to avoid jeopardizing federal funding, ensure the [http://tinyurl.com/pomq3xn| minimum tolerable limit is met for new or replacement bridges.] At a minimum, establish a bridge length that will not result in the bridge being classified as Functionally Obsolete.

==Roadway Configuration Under a Bridge==
The lane, shoulder, and sidewalk widths under the bridge should be consistent with the lane, shoulder, and sidewalk widths on the roadway beyond the bridge. The exception is when determining shoulder widths under a bridge. In these cases, the starting point should be the minimum horizontal underclearance to a substructure unit or concrete barrier. In general, shoulders under bridges should match the roadway width at the bridge if this is wider than the NBI requirements. (Add clearance to railroad tracks)

==Span Configuration==
The bridge span configuration should be evaluated to provide the most cost effective structure. For long bridges, options should be investigated with fewer piers, which would have lower substructure costs and higher superstructure costs, and compared to options with more piers, which would have higher substructure costs and lower superstructure costs, in order to find the most cost effective span configuration. For bridges crossing roadways, shoulder piers should be avoided since they create an obstruction and may prohibit future roadway widening. For bridges crossing waterways, piers should be kept out of the waterway if possible since they require dewatering and cofferdams for construction, are susceptible to scour, and can cause debris jams restricting flow potentially resulting in flooding. Removing debris is difficult for maintenance forces, as access to these areas is limited and often requires a permit. Keeping piers out of waterways is also a desirable practice from an environmental permitting standpoint. Refer to [[Bridge: Stream Crossings|Bridge: Stream Crossings]] for more information on Piers in waterways.

==Design for Future Considerations==
Prior to and throughout design, contact the appropriate MDOT regional planning office to identify any proposed future capacity improvements for the roadway or other facility the bridge is spanning that would result in the need for a longer bridge. The time frame for the proposed improvement should be considered. If the roadway or facility widening is likely in the next 20 years then accommodating the additional width with a longer bridge may be warranted depending on the project budget. In general, if the time frame is uncertain then the scope of the project may be limited to address only the current needs and requirements or consideration should be given to a structure design that will enable the bridge to be lengthened in the future.

==Capacity Improvement Project==
Major capital improvement projects often include replacing and lengthening existing bridges. When a roadway widening project impacts an existing overpass bridge, the initial thought may be to replace the bridge to span whatever roadway typical section is proposed, which may result in unnecessary cost. Depending on the existing bridge superelevation or profile, widening the roadway under it may reduce the vertical underclearance, making a full bridge replacement necessary. However, if this is not an issue and the bridge is in good condition and not expected to need major rehabilitation in the next 20 years, keeping the bridge may be an option. If the answer is yes to any of the following questions, then eliminating the bridge replacement should be strongly considered:
*Can shoulders or lane widths be narrowed under a bridge, without impacting the overall safety of the roadway, to avoid impacting shoulder piers or abutments, thus eliminating the need to replace the bridge overpass?
*Can retaining walls be added under a bridge to eliminate the need to replace the bridge overpass?
*Can the profile of the roadway or facility under the bridge be modified to meet minimum vertical underclearance criteria?

==Grading Under the Bridge==
Often proposed roadway typical sections include safety grading and drainage ditches, which can significantly increase bridge lengths. For bridges spanning over roadways, coordinate with the roadway designer to see if the safety grading and drainage ditches under the bridge can be eliminated and replaced with a concrete barrier at the shoulder edge that retains the fill slope. This will shorten the bridge length while still providing an open bridge. Similarly, when there are sidewalks under a bridge, consider placing a concrete barrier at the sidewalk edge with fill behind it, to help minimize the bridge length.

==Environmental Impacts==
Environmental entities often request that bridges be made longer to avoid impacts to wetlands, forests, floodplains, etc. Before agreeing to this, the benefits of avoiding the environmental features should be compared to the additional construction and maintenance costs of a longer bridge. For example, simply lengthening a bridge may not save the wetland if the wetland will be in the shadow of the bridge, causing all the vegetation to die. It may be more economical to build a shorter bridge and provide mitigation for the impacted wetland at another location, especially if the area of the wetland is relatively small. Another frequent request from environmental entities is to span the entire floodplain, resulting in bridges much longer that required from a structure hydraulics standpoint. Every effort should be made to keep the bridge only as long as it needs to be to meet the design requirements, while taking into account stream geomorphology, recreational use, and wildlife requirements.

[[Category:Practical Design Guidance]]

=See Also=
*[[Bridge: Width|Bridge: Width]]
*[[Bridge: Stream Crossings|Bridge: Stream Crossings]]
*[[Roadways: Facility Selection|Roadways: Facility Selection]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bridge: Length/Span Configuration

2016-12-07T20:00:49Z

LLBarry: /* Grading Under the Bridge */

{| class="wikitable"
|-
| colspan="3" |
'''Length/Span Configuration'''

|-
| colspan="3" |
=Primary Guidance=
*Provide a span configuration to accommodate the needs under the bridge while minimizing the height of supporting abutments
*Provide a minimum bridge horizontal under clearance so that the bridge is not classified as [http://tinyurl.com/otkjvhf| Functionally Obsolete]
*The lane, shoulder, and sidewalk widths under a bridge should be consistent with the roadway configuration beyond the bridge
*Provide a span configuration that provides the most cost effective structure
*Consider future capacity roadway or other facility (i.e. railroad, trail, etc.) improvements under a bridge and the timeframe for when those improvements are planned when determining the bridge length
*Where possible, eliminate drainage ditches and safety grading under a bridge and replace them with a concrete barrier supporting the fill slope to reduce bridge lengths
*When environmental entities request lengthening bridges to avoid environmental impacts, evaluate the benefits of avoiding the environmental feature compared to the cost of constructing and maintaining a longer bridge

|-
| colspan="3" |

=Discussion=

==General==
Bridge lengths shall be sufficient to span over the roadway or facility being crossed. Longer bridges with short abutments are preferred since they create an open structure while providing added safety in the ability to see beyond the bridge. Although this results in a bridge that is longer than it would need to be with full height abutments, the tall abutments and foundations costs generally offset the longer superstructure costs. Tall abutments, especially those located adjacent to a paved roadway, can also be visual obstructions and require additional impact damage protection. Shorter abutments make inspections easier, and the additional length provided under the bridge could be used to accommodate future widening, if needed.

==Functionally Obsolete==
All bridges are rated for [http://tinyurl.com/otkjvhf| functional criteria] to determine if a bridge is classified as [http://tinyurl.com/otkjvhf| Functionally Obsolete]. This includes horizontal under clearance, which evaluates clearance from the bridge substructure unit to the through roadway. The required minimum horizontal under clearance is based on the roadway type. A rating value from 0 to 9 is assigned with any rating below a 4, resulting in the bridge being classified as Functionally Obsolete. In order to avoid jeopardizing federal funding, ensure the [http://tinyurl.com/pomq3xn| minimum tolerable limit is met for new or replacement bridges.] At a minimum, establish a bridge length that will not result in the bridge being classified as Functionally Obsolete.

==Roadway Configuration Under a Bridge==
The lane, shoulder, and sidewalk widths under the bridge should be consistent with the lane, shoulder, and sidewalk widths on the roadway beyond the bridge. The exception is when determining shoulder widths under a bridge. In these cases, the starting point should be the minimum horizontal underclearance to a substructure unit or concrete barrier. In general, shoulders under bridges should match the roadway width at the bridge if this is wider than the NBI requirements. (Add clearance to railroad tracks)

==Span Configuration==
The bridge span configuration should be evaluated to provide the most cost effective structure. For long bridges, options should be investigated with fewer piers, which would have lower substructure costs and higher superstructure costs, and compared to options with more piers, which would have higher substructure costs and lower superstructure costs, in order to find the most cost effective span configuration. For bridges crossing roadways, shoulder piers should be avoided since they create an obstruction and may prohibit future roadway widening. For bridges crossing waterways, piers should be kept out of the waterway if possible since they require dewatering and cofferdams for construction, are susceptible to scour, and can cause debris jams restricting flow potentially resulting in flooding. Removing debris is difficult for maintenance forces, as access to these areas is limited and often requires a permit. Keeping piers out of waterways is also a desirable practice from an environmental permitting standpoint. Refer to [[Bridge: Stream Crossings|Bridge: Stream Crossings]] for more information on Piers in waterways.

==Design for Future Considerations==
Prior to and throughout design, contact the appropriate MDOT regional planning office to identify any proposed future capacity improvements for the roadway or other facility the bridge is spanning that would result in the need for a longer bridge. The time frame for the proposed improvement should be considered. If the roadway or facility widening is likely in the next 20 years then accommodating the additional width with a longer bridge may be warranted depending on the project budget. In general, if the time frame is uncertain then the scope of the project may be limited to address only the current needs and requirements or consideration should be given to a structure design that will enable the bridge to be lengthened in the future.

==Capacity Improvement Project==
Major capital improvement projects often include replacing and lengthening existing bridges. When a roadway widening project impacts an existing overpass bridge, the initial thought may be to replace the bridge to span whatever roadway typical section is proposed, which may result in unnecessary cost. Depending on the existing bridge superelevation or profile, widening the roadway under it may reduce the vertical underclearance, making a full bridge replacement necessary. However, if this is not an issue and the bridge is in good condition and not expected to need major rehabilitation in the next 20 years, keeping the bridge may be an option. If the answer is yes to any of the following questions, then eliminating the bridge replacement should be strongly considered:
*Can shoulders or lane widths be narrowed under a bridge, without impacting the overall safety of the roadway, to avoid impacting shoulder piers or abutments, thus eliminating the need to replace the bridge overpass?
*Can retaining walls be added under a bridge to eliminate the need to replace the bridge overpass?
*Can the profile of the roadway or facility under the bridge be modified to meet minimum vertical underclearance criteria?

==Grading Under the Bridge==
Often proposed roadway typical sections include safety grading and drainage ditches, which can significantly increase bridge lengths. For bridges spanning over roadways, coordinate with the roadway designer to see if the safety grading and drainage ditches under the bridge can be eliminated and replaced with a concrete barrier at the shoulder edge that retains the fill slope. This will shorten the bridge length while still providing an open bridge. Similarly, when there are sidewalks under a bridge, consider placing a concrete barrier at the sidewalk edge with fill behind it, to help minimize the bridge length.

==Environmental Impacts==
Environmental entities often request that bridges be made longer to avoid impacts to wetlands, forests, floodplains, etc. Before agreeing to this, the benefits of avoiding the environmental features should be compared to the additional construction and maintenance costs of a longer bridge. For example, simply lengthening a bridge may not save the wetland if the wetland will be in the shadow of the bridge, causing all the vegetation to die. It may be more economical to build a shorter bridge and provide mitigation for the impacted wetland at another location, especially if the area of the wetland is relatively small. Another frequent request from environmental entities is to span the entire floodplain, resulting in bridges much longer that required from a structure hydraulics standpoint. Every effort should be made to keep the bridge only as long as it needs to be to meet the design requirements , while taking into account stream geomorphology, recreational use, and wildlife requirements.

[[Category:Practical Design Guidance]]

=See Also=
*[[Bridge: Width|Bridge: Width]]
*[[Bridge: Stream Crossings|Bridge: Stream Crossings]]
*[[Roadways: Facility Selection|Roadways: Facility Selection]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bridge: Length/Span Configuration

2016-12-07T19:59:23Z

LLBarry: /* Span Configuration */

{| class="wikitable"
|-
| colspan="3" |
'''Length/Span Configuration'''

|-
| colspan="3" |
=Primary Guidance=
*Provide a span configuration to accommodate the needs under the bridge while minimizing the height of supporting abutments
*Provide a minimum bridge horizontal under clearance so that the bridge is not classified as [http://tinyurl.com/otkjvhf| Functionally Obsolete]
*The lane, shoulder, and sidewalk widths under a bridge should be consistent with the roadway configuration beyond the bridge
*Provide a span configuration that provides the most cost effective structure
*Consider future capacity roadway or other facility (i.e. railroad, trail, etc.) improvements under a bridge and the timeframe for when those improvements are planned when determining the bridge length
*Where possible, eliminate drainage ditches and safety grading under a bridge and replace them with a concrete barrier supporting the fill slope to reduce bridge lengths
*When environmental entities request lengthening bridges to avoid environmental impacts, evaluate the benefits of avoiding the environmental feature compared to the cost of constructing and maintaining a longer bridge

|-
| colspan="3" |

=Discussion=

==General==
Bridge lengths shall be sufficient to span over the roadway or facility being crossed. Longer bridges with short abutments are preferred since they create an open structure while providing added safety in the ability to see beyond the bridge. Although this results in a bridge that is longer than it would need to be with full height abutments, the tall abutments and foundations costs generally offset the longer superstructure costs. Tall abutments, especially those located adjacent to a paved roadway, can also be visual obstructions and require additional impact damage protection. Shorter abutments make inspections easier, and the additional length provided under the bridge could be used to accommodate future widening, if needed.

==Functionally Obsolete==
All bridges are rated for [http://tinyurl.com/otkjvhf| functional criteria] to determine if a bridge is classified as [http://tinyurl.com/otkjvhf| Functionally Obsolete]. This includes horizontal under clearance, which evaluates clearance from the bridge substructure unit to the through roadway. The required minimum horizontal under clearance is based on the roadway type. A rating value from 0 to 9 is assigned with any rating below a 4, resulting in the bridge being classified as Functionally Obsolete. In order to avoid jeopardizing federal funding, ensure the [http://tinyurl.com/pomq3xn| minimum tolerable limit is met for new or replacement bridges.] At a minimum, establish a bridge length that will not result in the bridge being classified as Functionally Obsolete.

==Roadway Configuration Under a Bridge==
The lane, shoulder, and sidewalk widths under the bridge should be consistent with the lane, shoulder, and sidewalk widths on the roadway beyond the bridge. The exception is when determining shoulder widths under a bridge. In these cases, the starting point should be the minimum horizontal underclearance to a substructure unit or concrete barrier. In general, shoulders under bridges should match the roadway width at the bridge if this is wider than the NBI requirements. (Add clearance to railroad tracks)

==Span Configuration==
The bridge span configuration should be evaluated to provide the most cost effective structure. For long bridges, options should be investigated with fewer piers, which would have lower substructure costs and higher superstructure costs, and compared to options with more piers, which would have higher substructure costs and lower superstructure costs, in order to find the most cost effective span configuration. For bridges crossing roadways, shoulder piers should be avoided since they create an obstruction and may prohibit future roadway widening. For bridges crossing waterways, piers should be kept out of the waterway if possible since they require dewatering and cofferdams for construction, are susceptible to scour, and can cause debris jams restricting flow potentially resulting in flooding. Removing debris is difficult for maintenance forces, as access to these areas is limited and often requires a permit. Keeping piers out of waterways is also a desirable practice from an environmental permitting standpoint. Refer to [[Bridge: Stream Crossings|Bridge: Stream Crossings]] for more information on Piers in waterways.

==Design for Future Considerations==
Prior to and throughout design, contact the appropriate MDOT regional planning office to identify any proposed future capacity improvements for the roadway or other facility the bridge is spanning that would result in the need for a longer bridge. The time frame for the proposed improvement should be considered. If the roadway or facility widening is likely in the next 20 years then accommodating the additional width with a longer bridge may be warranted depending on the project budget. In general, if the time frame is uncertain then the scope of the project may be limited to address only the current needs and requirements or consideration should be given to a structure design that will enable the bridge to be lengthened in the future.

==Capacity Improvement Project==
Major capital improvement projects often include replacing and lengthening existing bridges. When a roadway widening project impacts an existing overpass bridge, the initial thought may be to replace the bridge to span whatever roadway typical section is proposed, which may result in unnecessary cost. Depending on the existing bridge superelevation or profile, widening the roadway under it may reduce the vertical underclearance, making a full bridge replacement necessary. However, if this is not an issue and the bridge is in good condition and not expected to need major rehabilitation in the next 20 years, keeping the bridge may be an option. If the answer is yes to any of the following questions, then eliminating the bridge replacement should be strongly considered:
*Can shoulders or lane widths be narrowed under a bridge, without impacting the overall safety of the roadway, to avoid impacting shoulder piers or abutments, thus eliminating the need to replace the bridge overpass?
*Can retaining walls be added under a bridge to eliminate the need to replace the bridge overpass?
*Can the profile of the roadway or facility under the bridge be modified to meet minimum vertical underclearance criteria?

==Grading Under the Bridge==
Often proposed roadway typical sections include safety grading and drainage ditches, which can significantly increase bridge lengths. For bridges spanning over roadways, coordinate with the roadway designer to see if the safety grading and drainage ditches under the bridge can be eliminated and replaced with a concrete barrier at the shoulder edge that retains the fill slope. This will shorten the bridge length while still providing an open bridge. Similarly, when there are sidewalks under a bridge, consider placing a concrete barrier at the sidewalk edge with fill behind i, to help minimize the bridge length.

==Environmental Impacts==
Environmental entities often request that bridges be made longer to avoid impacts to wetlands, forests, floodplains, etc. Before agreeing to this, the benefits of avoiding the environmental features should be compared to the additional construction and maintenance costs of a longer bridge. For example, simply lengthening a bridge may not save the wetland if the wetland will be in the shadow of the bridge, causing all the vegetation to die. It may be more economical to build a shorter bridge and provide mitigation for the impacted wetland at another location, especially if the area of the wetland is relatively small. Another frequent request from environmental entities is to span the entire floodplain, resulting in bridges much longer that required from a structure hydraulics standpoint. Every effort should be made to keep the bridge only as long as it needs to be to meet the design requirements , while taking into account stream geomorphology, recreational use, and wildlife requirements.

[[Category:Practical Design Guidance]]

=See Also=
*[[Bridge: Width|Bridge: Width]]
*[[Bridge: Stream Crossings|Bridge: Stream Crossings]]
*[[Roadways: Facility Selection|Roadways: Facility Selection]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bridge: Length/Span Configuration

2016-12-07T19:58:39Z

LLBarry: /* Span Configuration */

{| class="wikitable"
|-
| colspan="3" |
'''Length/Span Configuration'''

|-
| colspan="3" |
=Primary Guidance=
*Provide a span configuration to accommodate the needs under the bridge while minimizing the height of supporting abutments
*Provide a minimum bridge horizontal under clearance so that the bridge is not classified as [http://tinyurl.com/otkjvhf| Functionally Obsolete]
*The lane, shoulder, and sidewalk widths under a bridge should be consistent with the roadway configuration beyond the bridge
*Provide a span configuration that provides the most cost effective structure
*Consider future capacity roadway or other facility (i.e. railroad, trail, etc.) improvements under a bridge and the timeframe for when those improvements are planned when determining the bridge length
*Where possible, eliminate drainage ditches and safety grading under a bridge and replace them with a concrete barrier supporting the fill slope to reduce bridge lengths
*When environmental entities request lengthening bridges to avoid environmental impacts, evaluate the benefits of avoiding the environmental feature compared to the cost of constructing and maintaining a longer bridge

|-
| colspan="3" |

=Discussion=

==General==
Bridge lengths shall be sufficient to span over the roadway or facility being crossed. Longer bridges with short abutments are preferred since they create an open structure while providing added safety in the ability to see beyond the bridge. Although this results in a bridge that is longer than it would need to be with full height abutments, the tall abutments and foundations costs generally offset the longer superstructure costs. Tall abutments, especially those located adjacent to a paved roadway, can also be visual obstructions and require additional impact damage protection. Shorter abutments make inspections easier, and the additional length provided under the bridge could be used to accommodate future widening, if needed.

==Functionally Obsolete==
All bridges are rated for [http://tinyurl.com/otkjvhf| functional criteria] to determine if a bridge is classified as [http://tinyurl.com/otkjvhf| Functionally Obsolete]. This includes horizontal under clearance, which evaluates clearance from the bridge substructure unit to the through roadway. The required minimum horizontal under clearance is based on the roadway type. A rating value from 0 to 9 is assigned with any rating below a 4, resulting in the bridge being classified as Functionally Obsolete. In order to avoid jeopardizing federal funding, ensure the [http://tinyurl.com/pomq3xn| minimum tolerable limit is met for new or replacement bridges.] At a minimum, establish a bridge length that will not result in the bridge being classified as Functionally Obsolete.

==Roadway Configuration Under a Bridge==
The lane, shoulder, and sidewalk widths under the bridge should be consistent with the lane, shoulder, and sidewalk widths on the roadway beyond the bridge. The exception is when determining shoulder widths under a bridge. In these cases, the starting point should be the minimum horizontal underclearance to a substructure unit or concrete barrier. In general, shoulders under bridges should match the roadway width at the bridge if this is wider than the NBI requirements. (Add clearance to railroad tracks)

==Span Configuration==
The bridge span configuration should be evaluated to provide the most cost effective structure. For long bridges, options should be investigated with fewer piers, which would have lower substructure costs and higher superstructure costs, and compared to options with more piers, which would have higher substructure costs and lower superstructure costs, in order to find the most cost effective span configuration. For bridges crossing roadways, shoulder piers should be avoided since they create an obstruction and may prohibit future roadway widening of the roadway. For bridges crossing waterways, piers should be kept out of the waterway if possible since they require dewatering and cofferdams for construction, are susceptible to scour, and can cause debris jams restricting flow potentially resulting in flooding. Removing debris is difficult for maintenance forces, as access to these areas is limited and often requires a permit. Keeping piers out of waterways is also a desirable practice from an environmental permitting standpoint. Refer to [[Bridge: Stream Crossings|Bridge: Stream Crossings]] for more information on Piers in waterways.

==Design for Future Considerations==
Prior to and throughout design, contact the appropriate MDOT regional planning office to identify any proposed future capacity improvements for the roadway or other facility the bridge is spanning that would result in the need for a longer bridge. The time frame for the proposed improvement should be considered. If the roadway or facility widening is likely in the next 20 years then accommodating the additional width with a longer bridge may be warranted depending on the project budget. In general, if the time frame is uncertain then the scope of the project may be limited to address only the current needs and requirements or consideration should be given to a structure design that will enable the bridge to be lengthened in the future.

==Capacity Improvement Project==
Major capital improvement projects often include replacing and lengthening existing bridges. When a roadway widening project impacts an existing overpass bridge, the initial thought may be to replace the bridge to span whatever roadway typical section is proposed, which may result in unnecessary cost. Depending on the existing bridge superelevation or profile, widening the roadway under it may reduce the vertical underclearance, making a full bridge replacement necessary. However, if this is not an issue and the bridge is in good condition and not expected to need major rehabilitation in the next 20 years, keeping the bridge may be an option. If the answer is yes to any of the following questions, then eliminating the bridge replacement should be strongly considered:
*Can shoulders or lane widths be narrowed under a bridge, without impacting the overall safety of the roadway, to avoid impacting shoulder piers or abutments, thus eliminating the need to replace the bridge overpass?
*Can retaining walls be added under a bridge to eliminate the need to replace the bridge overpass?
*Can the profile of the roadway or facility under the bridge be modified to meet minimum vertical underclearance criteria?

==Grading Under the Bridge==
Often proposed roadway typical sections include safety grading and drainage ditches, which can significantly increase bridge lengths. For bridges spanning over roadways, coordinate with the roadway designer to see if the safety grading and drainage ditches under the bridge can be eliminated and replaced with a concrete barrier at the shoulder edge that retains the fill slope. This will shorten the bridge length while still providing an open bridge. Similarly, when there are sidewalks under a bridge, consider placing a concrete barrier at the sidewalk edge with fill behind i, to help minimize the bridge length.

==Environmental Impacts==
Environmental entities often request that bridges be made longer to avoid impacts to wetlands, forests, floodplains, etc. Before agreeing to this, the benefits of avoiding the environmental features should be compared to the additional construction and maintenance costs of a longer bridge. For example, simply lengthening a bridge may not save the wetland if the wetland will be in the shadow of the bridge, causing all the vegetation to die. It may be more economical to build a shorter bridge and provide mitigation for the impacted wetland at another location, especially if the area of the wetland is relatively small. Another frequent request from environmental entities is to span the entire floodplain, resulting in bridges much longer that required from a structure hydraulics standpoint. Every effort should be made to keep the bridge only as long as it needs to be to meet the design requirements , while taking into account stream geomorphology, recreational use, and wildlife requirements.

[[Category:Practical Design Guidance]]

=See Also=
*[[Bridge: Width|Bridge: Width]]
*[[Bridge: Stream Crossings|Bridge: Stream Crossings]]
*[[Roadways: Facility Selection|Roadways: Facility Selection]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bridge: Length/Span Configuration

2016-12-07T19:58:23Z

LLBarry: /* Roadway Configuration Under a Bridge */

{| class="wikitable"
|-
| colspan="3" |
'''Length/Span Configuration'''

|-
| colspan="3" |
=Primary Guidance=
*Provide a span configuration to accommodate the needs under the bridge while minimizing the height of supporting abutments
*Provide a minimum bridge horizontal under clearance so that the bridge is not classified as [http://tinyurl.com/otkjvhf| Functionally Obsolete]
*The lane, shoulder, and sidewalk widths under a bridge should be consistent with the roadway configuration beyond the bridge
*Provide a span configuration that provides the most cost effective structure
*Consider future capacity roadway or other facility (i.e. railroad, trail, etc.) improvements under a bridge and the timeframe for when those improvements are planned when determining the bridge length
*Where possible, eliminate drainage ditches and safety grading under a bridge and replace them with a concrete barrier supporting the fill slope to reduce bridge lengths
*When environmental entities request lengthening bridges to avoid environmental impacts, evaluate the benefits of avoiding the environmental feature compared to the cost of constructing and maintaining a longer bridge

|-
| colspan="3" |

=Discussion=

==General==
Bridge lengths shall be sufficient to span over the roadway or facility being crossed. Longer bridges with short abutments are preferred since they create an open structure while providing added safety in the ability to see beyond the bridge. Although this results in a bridge that is longer than it would need to be with full height abutments, the tall abutments and foundations costs generally offset the longer superstructure costs. Tall abutments, especially those located adjacent to a paved roadway, can also be visual obstructions and require additional impact damage protection. Shorter abutments make inspections easier, and the additional length provided under the bridge could be used to accommodate future widening, if needed.

==Functionally Obsolete==
All bridges are rated for [http://tinyurl.com/otkjvhf| functional criteria] to determine if a bridge is classified as [http://tinyurl.com/otkjvhf| Functionally Obsolete]. This includes horizontal under clearance, which evaluates clearance from the bridge substructure unit to the through roadway. The required minimum horizontal under clearance is based on the roadway type. A rating value from 0 to 9 is assigned with any rating below a 4, resulting in the bridge being classified as Functionally Obsolete. In order to avoid jeopardizing federal funding, ensure the [http://tinyurl.com/pomq3xn| minimum tolerable limit is met for new or replacement bridges.] At a minimum, establish a bridge length that will not result in the bridge being classified as Functionally Obsolete.

==Roadway Configuration Under a Bridge==
The lane, shoulder, and sidewalk widths under the bridge should be consistent with the lane, shoulder, and sidewalk widths on the roadway beyond the bridge. The exception is when determining shoulder widths under a bridge. In these cases, the starting point should be the minimum horizontal underclearance to a substructure unit or concrete barrier. In general, shoulders under bridges should match the roadway width at the bridge if this is wider than the NBI requirements. (Add clearance to railroad tracks)

==Span Configuration==
The bridge span configuration should evaluated to provide the most cost effective structure. For long bridges, options should be investigated with fewer piers, which would have lower substructure costs and higher superstructure costs, and compared to options with more piers, which would have higher substructure costs and lower superstructure costs, in order to find the most cost effective span configuration. For bridges crossing roadways, shoulder piers should be avoided since they create an obstruction and may prohibit future roadway widening of the roadway. For bridges crossing waterways, piers should be kept out of the waterway if possible since they require dewatering and cofferdams for construction, are susceptible to scour, and can cause debris jams restricting flow potentially resulting in flooding. Removing debris is difficult for maintenance forces, as access to these areas is limited and often requires a permit. Keeping piers out of waterways is also a desirable practice from an environmental permitting standpoint. Refer to [[Bridge: Stream Crossings|Bridge: Stream Crossings]] for more information on Piers in waterways.

==Design for Future Considerations==
Prior to and throughout design, contact the appropriate MDOT regional planning office to identify any proposed future capacity improvements for the roadway or other facility the bridge is spanning that would result in the need for a longer bridge. The time frame for the proposed improvement should be considered. If the roadway or facility widening is likely in the next 20 years then accommodating the additional width with a longer bridge may be warranted depending on the project budget. In general, if the time frame is uncertain then the scope of the project may be limited to address only the current needs and requirements or consideration should be given to a structure design that will enable the bridge to be lengthened in the future.

==Capacity Improvement Project==
Major capital improvement projects often include replacing and lengthening existing bridges. When a roadway widening project impacts an existing overpass bridge, the initial thought may be to replace the bridge to span whatever roadway typical section is proposed, which may result in unnecessary cost. Depending on the existing bridge superelevation or profile, widening the roadway under it may reduce the vertical underclearance, making a full bridge replacement necessary. However, if this is not an issue and the bridge is in good condition and not expected to need major rehabilitation in the next 20 years, keeping the bridge may be an option. If the answer is yes to any of the following questions, then eliminating the bridge replacement should be strongly considered:
*Can shoulders or lane widths be narrowed under a bridge, without impacting the overall safety of the roadway, to avoid impacting shoulder piers or abutments, thus eliminating the need to replace the bridge overpass?
*Can retaining walls be added under a bridge to eliminate the need to replace the bridge overpass?
*Can the profile of the roadway or facility under the bridge be modified to meet minimum vertical underclearance criteria?

==Grading Under the Bridge==
Often proposed roadway typical sections include safety grading and drainage ditches, which can significantly increase bridge lengths. For bridges spanning over roadways, coordinate with the roadway designer to see if the safety grading and drainage ditches under the bridge can be eliminated and replaced with a concrete barrier at the shoulder edge that retains the fill slope. This will shorten the bridge length while still providing an open bridge. Similarly, when there are sidewalks under a bridge, consider placing a concrete barrier at the sidewalk edge with fill behind i, to help minimize the bridge length.

==Environmental Impacts==
Environmental entities often request that bridges be made longer to avoid impacts to wetlands, forests, floodplains, etc. Before agreeing to this, the benefits of avoiding the environmental features should be compared to the additional construction and maintenance costs of a longer bridge. For example, simply lengthening a bridge may not save the wetland if the wetland will be in the shadow of the bridge, causing all the vegetation to die. It may be more economical to build a shorter bridge and provide mitigation for the impacted wetland at another location, especially if the area of the wetland is relatively small. Another frequent request from environmental entities is to span the entire floodplain, resulting in bridges much longer that required from a structure hydraulics standpoint. Every effort should be made to keep the bridge only as long as it needs to be to meet the design requirements , while taking into account stream geomorphology, recreational use, and wildlife requirements.

[[Category:Practical Design Guidance]]

=See Also=
*[[Bridge: Width|Bridge: Width]]
*[[Bridge: Stream Crossings|Bridge: Stream Crossings]]
*[[Roadways: Facility Selection|Roadways: Facility Selection]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bridge: Length/Span Configuration

2016-12-07T19:57:39Z

LLBarry: /* General */

{| class="wikitable"
|-
| colspan="3" |
'''Length/Span Configuration'''

|-
| colspan="3" |
=Primary Guidance=
*Provide a span configuration to accommodate the needs under the bridge while minimizing the height of supporting abutments
*Provide a minimum bridge horizontal under clearance so that the bridge is not classified as [http://tinyurl.com/otkjvhf| Functionally Obsolete]
*The lane, shoulder, and sidewalk widths under a bridge should be consistent with the roadway configuration beyond the bridge
*Provide a span configuration that provides the most cost effective structure
*Consider future capacity roadway or other facility (i.e. railroad, trail, etc.) improvements under a bridge and the timeframe for when those improvements are planned when determining the bridge length
*Where possible, eliminate drainage ditches and safety grading under a bridge and replace them with a concrete barrier supporting the fill slope to reduce bridge lengths
*When environmental entities request lengthening bridges to avoid environmental impacts, evaluate the benefits of avoiding the environmental feature compared to the cost of constructing and maintaining a longer bridge

|-
| colspan="3" |

=Discussion=

==General==
Bridge lengths shall be sufficient to span over the roadway or facility being crossed. Longer bridges with short abutments are preferred since they create an open structure while providing added safety in the ability to see beyond the bridge. Although this results in a bridge that is longer than it would need to be with full height abutments, the tall abutments and foundations costs generally offset the longer superstructure costs. Tall abutments, especially those located adjacent to a paved roadway, can also be visual obstructions and require additional impact damage protection. Shorter abutments make inspections easier, and the additional length provided under the bridge could be used to accommodate future widening, if needed.

==Functionally Obsolete==
All bridges are rated for [http://tinyurl.com/otkjvhf| functional criteria] to determine if a bridge is classified as [http://tinyurl.com/otkjvhf| Functionally Obsolete]. This includes horizontal under clearance, which evaluates clearance from the bridge substructure unit to the through roadway. The required minimum horizontal under clearance is based on the roadway type. A rating value from 0 to 9 is assigned with any rating below a 4, resulting in the bridge being classified as Functionally Obsolete. In order to avoid jeopardizing federal funding, ensure the [http://tinyurl.com/pomq3xn| minimum tolerable limit is met for new or replacement bridges.] At a minimum, establish a bridge length that will not result in the bridge being classified as Functionally Obsolete.

==Roadway Configuration Under a Bridge==
The lane, shoulder, and sidewalk widths under the bridge should be consistent with the lane, shoulder, and sidewalk widths on the roadway beyond the bridge. The exception is when determining shoulder widths under a bridge. In these cases, the starting point should be the minimum horizontal underclearance to a substructure unit or concrete barrier . In general, shoulders under bridges should match the roadway width at the bridge if this is wider than the NBI requirements. (Add clearance to railroad tracks)

==Span Configuration==
The bridge span configuration should evaluated to provide the most cost effective structure. For long bridges, options should be investigated with fewer piers, which would have lower substructure costs and higher superstructure costs, and compared to options with more piers, which would have higher substructure costs and lower superstructure costs, in order to find the most cost effective span configuration. For bridges crossing roadways, shoulder piers should be avoided since they create an obstruction and may prohibit future roadway widening of the roadway. For bridges crossing waterways, piers should be kept out of the waterway if possible since they require dewatering and cofferdams for construction, are susceptible to scour, and can cause debris jams restricting flow potentially resulting in flooding. Removing debris is difficult for maintenance forces, as access to these areas is limited and often requires a permit. Keeping piers out of waterways is also a desirable practice from an environmental permitting standpoint. Refer to [[Bridge: Stream Crossings|Bridge: Stream Crossings]] for more information on Piers in waterways.

==Design for Future Considerations==
Prior to and throughout design, contact the appropriate MDOT regional planning office to identify any proposed future capacity improvements for the roadway or other facility the bridge is spanning that would result in the need for a longer bridge. The time frame for the proposed improvement should be considered. If the roadway or facility widening is likely in the next 20 years then accommodating the additional width with a longer bridge may be warranted depending on the project budget. In general, if the time frame is uncertain then the scope of the project may be limited to address only the current needs and requirements or consideration should be given to a structure design that will enable the bridge to be lengthened in the future.

==Capacity Improvement Project==
Major capital improvement projects often include replacing and lengthening existing bridges. When a roadway widening project impacts an existing overpass bridge, the initial thought may be to replace the bridge to span whatever roadway typical section is proposed, which may result in unnecessary cost. Depending on the existing bridge superelevation or profile, widening the roadway under it may reduce the vertical underclearance, making a full bridge replacement necessary. However, if this is not an issue and the bridge is in good condition and not expected to need major rehabilitation in the next 20 years, keeping the bridge may be an option. If the answer is yes to any of the following questions, then eliminating the bridge replacement should be strongly considered:
*Can shoulders or lane widths be narrowed under a bridge, without impacting the overall safety of the roadway, to avoid impacting shoulder piers or abutments, thus eliminating the need to replace the bridge overpass?
*Can retaining walls be added under a bridge to eliminate the need to replace the bridge overpass?
*Can the profile of the roadway or facility under the bridge be modified to meet minimum vertical underclearance criteria?

==Grading Under the Bridge==
Often proposed roadway typical sections include safety grading and drainage ditches, which can significantly increase bridge lengths. For bridges spanning over roadways, coordinate with the roadway designer to see if the safety grading and drainage ditches under the bridge can be eliminated and replaced with a concrete barrier at the shoulder edge that retains the fill slope. This will shorten the bridge length while still providing an open bridge. Similarly, when there are sidewalks under a bridge, consider placing a concrete barrier at the sidewalk edge with fill behind i, to help minimize the bridge length.

==Environmental Impacts==
Environmental entities often request that bridges be made longer to avoid impacts to wetlands, forests, floodplains, etc. Before agreeing to this, the benefits of avoiding the environmental features should be compared to the additional construction and maintenance costs of a longer bridge. For example, simply lengthening a bridge may not save the wetland if the wetland will be in the shadow of the bridge, causing all the vegetation to die. It may be more economical to build a shorter bridge and provide mitigation for the impacted wetland at another location, especially if the area of the wetland is relatively small. Another frequent request from environmental entities is to span the entire floodplain, resulting in bridges much longer that required from a structure hydraulics standpoint. Every effort should be made to keep the bridge only as long as it needs to be to meet the design requirements , while taking into account stream geomorphology, recreational use, and wildlife requirements.

[[Category:Practical Design Guidance]]

=See Also=
*[[Bridge: Width|Bridge: Width]]
*[[Bridge: Stream Crossings|Bridge: Stream Crossings]]
*[[Roadways: Facility Selection|Roadways: Facility Selection]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bridge: Length/Span Configuration

2016-12-07T19:57:22Z

LLBarry: /* Functionally Obsolete */

{| class="wikitable"
|-
| colspan="3" |
'''Length/Span Configuration'''

|-
| colspan="3" |
=Primary Guidance=
*Provide a span configuration to accommodate the needs under the bridge while minimizing the height of supporting abutments
*Provide a minimum bridge horizontal under clearance so that the bridge is not classified as [http://tinyurl.com/otkjvhf| Functionally Obsolete]
*The lane, shoulder, and sidewalk widths under a bridge should be consistent with the roadway configuration beyond the bridge
*Provide a span configuration that provides the most cost effective structure
*Consider future capacity roadway or other facility (i.e. railroad, trail, etc.) improvements under a bridge and the timeframe for when those improvements are planned when determining the bridge length
*Where possible, eliminate drainage ditches and safety grading under a bridge and replace them with a concrete barrier supporting the fill slope to reduce bridge lengths
*When environmental entities request lengthening bridges to avoid environmental impacts, evaluate the benefits of avoiding the environmental feature compared to the cost of constructing and maintaining a longer bridge

|-
| colspan="3" |

=Discussion=

==General==
Bridge lengths shall be sufficient to span over the roadway or facility being crossed. Longer bridges with short abutments are preferred since they create an open structure while providing added safety in the ability to see beyond the bridge. Although this results in a bridge that is longer than it would need to be with full height abutments, the tall abutments and foundations costs generally offset the longer superstructure costs. Tall abutments, especially those located adjacent to a paved roadway, can also be visual obstructions and require additional impact damage protection. Shorter abutments make inspections easier, and the additional length provided under the bridge could be used to accommodate future widening , if needed.

==Functionally Obsolete==
All bridges are rated for [http://tinyurl.com/otkjvhf| functional criteria] to determine if a bridge is classified as [http://tinyurl.com/otkjvhf| Functionally Obsolete]. This includes horizontal under clearance, which evaluates clearance from the bridge substructure unit to the through roadway. The required minimum horizontal under clearance is based on the roadway type. A rating value from 0 to 9 is assigned with any rating below a 4, resulting in the bridge being classified as Functionally Obsolete. In order to avoid jeopardizing federal funding, ensure the [http://tinyurl.com/pomq3xn| minimum tolerable limit is met for new or replacement bridges.] At a minimum, establish a bridge length that will not result in the bridge being classified as Functionally Obsolete.

==Roadway Configuration Under a Bridge==
The lane, shoulder, and sidewalk widths under the bridge should be consistent with the lane, shoulder, and sidewalk widths on the roadway beyond the bridge. The exception is when determining shoulder widths under a bridge. In these cases, the starting point should be the minimum horizontal underclearance to a substructure unit or concrete barrier . In general, shoulders under bridges should match the roadway width at the bridge if this is wider than the NBI requirements. (Add clearance to railroad tracks)

==Span Configuration==
The bridge span configuration should evaluated to provide the most cost effective structure. For long bridges, options should be investigated with fewer piers, which would have lower substructure costs and higher superstructure costs, and compared to options with more piers, which would have higher substructure costs and lower superstructure costs, in order to find the most cost effective span configuration. For bridges crossing roadways, shoulder piers should be avoided since they create an obstruction and may prohibit future roadway widening of the roadway. For bridges crossing waterways, piers should be kept out of the waterway if possible since they require dewatering and cofferdams for construction, are susceptible to scour, and can cause debris jams restricting flow potentially resulting in flooding. Removing debris is difficult for maintenance forces, as access to these areas is limited and often requires a permit. Keeping piers out of waterways is also a desirable practice from an environmental permitting standpoint. Refer to [[Bridge: Stream Crossings|Bridge: Stream Crossings]] for more information on Piers in waterways.

==Design for Future Considerations==
Prior to and throughout design, contact the appropriate MDOT regional planning office to identify any proposed future capacity improvements for the roadway or other facility the bridge is spanning that would result in the need for a longer bridge. The time frame for the proposed improvement should be considered. If the roadway or facility widening is likely in the next 20 years then accommodating the additional width with a longer bridge may be warranted depending on the project budget. In general, if the time frame is uncertain then the scope of the project may be limited to address only the current needs and requirements or consideration should be given to a structure design that will enable the bridge to be lengthened in the future.

==Capacity Improvement Project==
Major capital improvement projects often include replacing and lengthening existing bridges. When a roadway widening project impacts an existing overpass bridge, the initial thought may be to replace the bridge to span whatever roadway typical section is proposed, which may result in unnecessary cost. Depending on the existing bridge superelevation or profile, widening the roadway under it may reduce the vertical underclearance, making a full bridge replacement necessary. However, if this is not an issue and the bridge is in good condition and not expected to need major rehabilitation in the next 20 years, keeping the bridge may be an option. If the answer is yes to any of the following questions, then eliminating the bridge replacement should be strongly considered:
*Can shoulders or lane widths be narrowed under a bridge, without impacting the overall safety of the roadway, to avoid impacting shoulder piers or abutments, thus eliminating the need to replace the bridge overpass?
*Can retaining walls be added under a bridge to eliminate the need to replace the bridge overpass?
*Can the profile of the roadway or facility under the bridge be modified to meet minimum vertical underclearance criteria?

==Grading Under the Bridge==
Often proposed roadway typical sections include safety grading and drainage ditches, which can significantly increase bridge lengths. For bridges spanning over roadways, coordinate with the roadway designer to see if the safety grading and drainage ditches under the bridge can be eliminated and replaced with a concrete barrier at the shoulder edge that retains the fill slope. This will shorten the bridge length while still providing an open bridge. Similarly, when there are sidewalks under a bridge, consider placing a concrete barrier at the sidewalk edge with fill behind i, to help minimize the bridge length.

==Environmental Impacts==
Environmental entities often request that bridges be made longer to avoid impacts to wetlands, forests, floodplains, etc. Before agreeing to this, the benefits of avoiding the environmental features should be compared to the additional construction and maintenance costs of a longer bridge. For example, simply lengthening a bridge may not save the wetland if the wetland will be in the shadow of the bridge, causing all the vegetation to die. It may be more economical to build a shorter bridge and provide mitigation for the impacted wetland at another location, especially if the area of the wetland is relatively small. Another frequent request from environmental entities is to span the entire floodplain, resulting in bridges much longer that required from a structure hydraulics standpoint. Every effort should be made to keep the bridge only as long as it needs to be to meet the design requirements , while taking into account stream geomorphology, recreational use, and wildlife requirements.

[[Category:Practical Design Guidance]]

=See Also=
*[[Bridge: Width|Bridge: Width]]
*[[Bridge: Stream Crossings|Bridge: Stream Crossings]]
*[[Roadways: Facility Selection|Roadways: Facility Selection]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bridge: Construction Staging

2016-12-07T19:56:16Z

LLBarry: /* Future Deck Replacements */

{| class="wikitable"
|-
| colspan="3" |
'''Construction Staging'''

|-
| colspan="3" |
=Primary Guidance=
*When a bridge is being replaced or rehabilitated, the number of construction stages should be kept to a minimum.
*Whenever possible, bridges should be closed and traffic detoured during construction.
*Bridge substructures and superstructures should be designed to facilitate staged construction for a future deck replacement.

|-
| colspan="3" |

=Discussion=

==Stages of Construction==
When a bridge is being replaced or rehabilitated, the number of construction stages should be kept to a minimum, which will reduce the bridge cost and construction duration. Consider reducing the number of lanes being maintained and lane widths to accomplish this. If possible, avoid a situation where there is a construction zone in between travel lanes. This would make construction more difficult, increase the cost, and decrease safety for construction personnel and the traveling public.

==Detours==
Whenever possible, the bridge should be closed during construction and traffic detoured. This provides the shortest construction duration and lowest project cost while ensuring the safest project. For example, consider a detour for projects where the bridge can be constructed over the summer months when school is not in session and traffic needs are less. A detailed Maintenance of Traffic Alternatives Analysis should be performed when a detour is considered to ensure minimum mobility thresholds can be met. Consider drive by businesses that will be bypassed by the detour as well. A contractor incentive/disincentive to open the bridge to traffic on time should also be included in the project to minimize the impacts to the traveling public.

==Future Deck Replacements==
In order to address maintenance of traffic during a future bridge deck replacement, all substructure units on new bridges should be designed to support full live load with portions of the superstructure completely removed. If it is not apparent how many lanes may need to be maintained in the future, assume the bridge deck will be replaced in half sections for the purpose of the design. Piers should be configured so that temporary supports of pier caps will not be needed during staged construction. Where possible, the superstructure of the bridge should be arranged so that at least three beams will be supporting the deck in each stage of construction. Supporting the deck on two beams may not be a stable configuration, especially if curved girders are involved, and should be evaluated to determine if additional supports are required.

[[Category:Practical Design Guidance]]

=See Also=

*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bridge: Construction Staging

2016-12-07T19:55:57Z

LLBarry: /* Stages of Construction */

{| class="wikitable"
|-
| colspan="3" |
'''Construction Staging'''

|-
| colspan="3" |
=Primary Guidance=
*When a bridge is being replaced or rehabilitated, the number of construction stages should be kept to a minimum.
*Whenever possible, bridges should be closed and traffic detoured during construction.
*Bridge substructures and superstructures should be designed to facilitate staged construction for a future deck replacement.

|-
| colspan="3" |

=Discussion=

==Stages of Construction==
When a bridge is being replaced or rehabilitated, the number of construction stages should be kept to a minimum, which will reduce the bridge cost and construction duration. Consider reducing the number of lanes being maintained and lane widths to accomplish this. If possible, avoid a situation where there is a construction zone in between travel lanes. This would make construction more difficult, increase the cost, and decrease safety for construction personnel and the traveling public.

==Detours==
Whenever possible, the bridge should be closed during construction and traffic detoured. This provides the shortest construction duration and lowest project cost while ensuring the safest project. For example, consider a detour for projects where the bridge can be constructed over the summer months when school is not in session and traffic needs are less. A detailed Maintenance of Traffic Alternatives Analysis should be performed when a detour is considered to ensure minimum mobility thresholds can be met. Consider drive by businesses that will be bypassed by the detour as well. A contractor incentive/disincentive to open the bridge to traffic on time should also be included in the project to minimize the impacts to the traveling public.

==Future Deck Replacements==
In order to address maintenance of traffic during a future bridge deck replacement, all substructure units on new bridges should be designed to support full live load with portions of the superstructure completely removed. If it is not apparent how many lanes may need to be maintained in the future, assume the bridge deck will be replaced in half sections for the purpose of the design. Piers should be configured so that temporary supports of pier caps will not be needed during staged construction. Where possible, the superstructure of the bridge should be arranged so that at least three beams will be supporting the deck in each stage of construction. Supporting the deck on two beams may not be a stable configuration, especially if curved girders are involved, and should be evaluated to see if additional supports are required.

[[Category:Practical Design Guidance]]

=See Also=

*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bridge: Retaining Walls

2016-12-07T19:54:32Z

LLBarry: /* Proprietary Retaining Walls */

{| class="wikitable"
|-
| colspan="3" |
'''Retaining Walls'''

|-
| colspan="3" |
=Primary Guidance=
*Retaining walls should be eliminated whenever possible and replaced with slopes
*Minimize the length and height of retaining walls
*Consider using proprietary retaining walls to speed up construction and reduce cost
*Select a wall type that can be constructed without temporary support of excavation
*When environmental entities request retaining walls to avoid environmental impacts, evaluate the benefits of avoiding the environmental feature compared to the cost of the wall and alternative mitigation

|-
| colspan="3" |

=Discussion=

==General==
The project need for retaining walls is typically identified when cut or fill slopes fall outside the State’s right-of-way. Whenever possible, these walls should be eliminated and replaced with slopes, which are less expensive and can be less intrusive than retaining walls. Generally, retaining walls should only be considered when the value of the right-of-way or other resource being impacted exceeds the cost of the wall.

==Slope Considerations==
Typically, 2:1 slopes are used in roadway construction, but different slopes should be considered when attempting to eliminate walls. Depending on the circumstances:
*Use Steeper Slopes
Using reinforced slopes steeper than 2:1 such as riprap slopes or engineered Mechanically Stabilized Earth (MSE) slopes to reduce or eliminate walls. These slope types can be considered unattractive, so consideration may need to be given to the importance of aesthetics for the location.
*Use Flatter Slopes and Obtain Slope Easements
Flattening the slope may result in larger impacts from a right-of-way perspective, but would have less visual impact and would be easier to maintain for a property owner. Instead of purchasing right-of-way for flat slopes, slope easements could be used that would still give a property owner the use of the slope area.

==Length and Height==
It may not be feasible to eliminate walls completely, but even eliminating portions of walls by adjusting the slope or purchasing right-of-way can result in cost savings. Retaining walls should be kept as short as possible. When feasible, the wall should be placed at the bottom of a slope instead of along the roadway or other facility edge. Placing the wall at the bottom roadway embankment slope as opposed to at the top of the slope eliminates having to place a roadway barrier on top of the wall and eliminates the need to design the wall for an impact load, which factors greatly in the structural design of the wall. A situation where retaining walls should not be placed at the bottom of a slope is when there are storm water management facilities at the top of the slope, since it is never desirable to have water stored behind a retaining wall.

==Proprietary Retaining Walls==
Proprietary retaining walls such as MSE Walls or Modular Block walls can be used as a cost effective alternative to cast in place walls and to speed up construction; however, they are not practical for all situations. When proprietary retaining walls are used on a project, the contract documents should be specific in stating which ones will be allowed. Consider the following when using proprietary walls:
*Segmental Retaining Walls (i.e. MSE, Modular Block) contain reinforcement straps that extend behind the wall face and are the most cost effective in locations where the wall is infill. When these types of walls are placed in cut areas, supporting excavation is usually required to install the reinforcement straps, which often extend back behind the wall a distance almost equal to the height of the wall reducing the cost savings as compared to a cast in place wall. These types of retaining walls may require additional right-of-way if the reinforcement straps extend beyond the right-of-way.
*The aesthetic details of a project can affect the type of proprietary wall that should be specified. MSE walls typically have large flat concrete panels, which can accept a form liner pattern. The blocks in Modular Block walls are much smaller, and while they can have roughened texture or different colors, they cannot accept a form liner patterns.
*Propriety retaining walls often have height limitations. A list of preapproved proprietary retaining walls is available at http://www.roads.maryland.gov/obd/MSEWallList.pdf, which includes the maximum allowable heights for these walls and can be used as a reference.
*While proprietary retaining wall manufacturers provide the wall design, they often leave the wall’s global stability responsibility to the owner. This needs to be investigated to determine if the wall type is feasible or if improvements need to be made to the wall(s) foundation, which could reduce the cost savings as compared to a cast in place wall.

==Soldier Pile and Lagging Walls==
Soldier pile and lagging walls consist of steel piles embedded in concrete caissons, with concrete lagging spanning between the piles. A non-structural concrete fascia can be cast on the outside face of the wall for aesthetic purposes. These walls are the most cost effective when used in areas where the wall is in a cut since they do not require a separate structure for support of excavation. Height can be a concern since these walls require tiebacks when they get tall, which can become expensive and may reduce the cost savings when comparing this wall type to others. Only concrete lagging should be used in permanent soldier pile and lagging walls. While this is more expensive than timber lagging, it will be more durable and have less maintenance problems in the future.

==Avoiding Environmental Impacts==
Often environmental entities request that retaining walls be constructed to avoid impacts to wetlands, forests, floodplains, etc. Before agreeing to this, the benefits of avoiding the environmental feature should be compared to the wall cost and alternative mitigation. Consideration should also be given to whether or not the wall will actually reduce the impacts to the environment. For example, a tall retaining wall may not save a wetland if the wetland will be in the shadow of the wall, causing all the vegetation to die. Similarly, the wall may cut off the flow of water through the wetland, adversely impacting the wetland. It may make more sense to eliminate the wall and provide mitigation for the impacted wetland at another location, especially if the area of the wetland is relatively small.

|}

=See Also=

*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bridge: Retaining Walls

2016-12-07T19:50:21Z

LLBarry: /* Length and Height */

{| class="wikitable"
|-
| colspan="3" |
'''Retaining Walls'''

|-
| colspan="3" |
=Primary Guidance=
*Retaining walls should be eliminated whenever possible and replaced with slopes
*Minimize the length and height of retaining walls
*Consider using proprietary retaining walls to speed up construction and reduce cost
*Select a wall type that can be constructed without temporary support of excavation
*When environmental entities request retaining walls to avoid environmental impacts, evaluate the benefits of avoiding the environmental feature compared to the cost of the wall and alternative mitigation

|-
| colspan="3" |

=Discussion=

==General==
The project need for retaining walls is typically identified when cut or fill slopes fall outside the State’s right-of-way. Whenever possible, these walls should be eliminated and replaced with slopes, which are less expensive and can be less intrusive than retaining walls. Generally, retaining walls should only be considered when the value of the right-of-way or other resource being impacted exceeds the cost of the wall.

==Slope Considerations==
Typically, 2:1 slopes are used in roadway construction, but different slopes should be considered when attempting to eliminate walls. Depending on the circumstances:
*Use Steeper Slopes
Using reinforced slopes steeper than 2:1 such as riprap slopes or engineered Mechanically Stabilized Earth (MSE) slopes to reduce or eliminate walls. These slope types can be considered unattractive, so consideration may need to be given to the importance of aesthetics for the location.
*Use Flatter Slopes and Obtain Slope Easements
Flattening the slope may result in larger impacts from a right-of-way perspective, but would have less visual impact and would be easier to maintain for a property owner. Instead of purchasing right-of-way for flat slopes, slope easements could be used that would still give a property owner the use of the slope area.

==Length and Height==
It may not be feasible to eliminate walls completely, but even eliminating portions of walls by adjusting the slope or purchasing right-of-way can result in cost savings. Retaining walls should be kept as short as possible. When feasible, the wall should be placed at the bottom of a slope instead of along the roadway or other facility edge. Placing the wall at the bottom roadway embankment slope as opposed to at the top of the slope eliminates having to place a roadway barrier on top of the wall and eliminates the need to design the wall for an impact load, which factors greatly in the structural design of the wall. A situation where retaining walls should not be placed at the bottom of a slope is when there are storm water management facilities at the top of the slope, since it is never desirable to have water stored behind a retaining wall.

==Proprietary Retaining Walls==
Proprietary retaining walls such as MSE Walls or Modular Block walls can be used as a cost effective alternative to cast in place walls and to speed up construction; however, they are not practical for all situations. When proprietary retaining walls are used on a project, the contract documents should be specific in stating which ones will be allowed. Consider the following when using proprietary walls:
*Segmental Retaining Walls (i.e. MSE, Modular Block) contain reinforcement straps that extend behind the wall face and are the most cost effective in locations where the wall is in fill. When these types of walls are placed in cut areas, supporting excavation is usually required to install the reinforcement straps, which often extend back behind the wall a distance almost equal to the height of the wall reducing the cost savings as compared to a cast in place wall. These types of retaining walls may require additional right-of-way if the reinforcement straps extend beyond the right-of-way.
*The aesthetic details of a project can affect the type of proprietary wall that should be specified. MSE walls typically have large flat concrete panels, which can accept a form liner pattern. The blocks in Modular Block walls are much smaller, and while they can have roughened texture or different colors, they cannot accept a form liner patterns.
*Propriety retaining walls often have height limitations. A list of preapproved proprietary retaining walls is available at http://www.roads.maryland.gov/obd/MSEWallList.pdf, which includes the maximum allowable heights for these walls and can be used as a reference.
*While proprietary retaining wall manufacturers provide the wall design, they often leave the wall’s global stability responsibility to the owner. This needs to be investigated to determine if the wall type is feasible or if improvements need to be made to the wall(s) foundation, which could reduce the cost savings as compared to a cast in place wall.

==Soldier Pile and Lagging Walls==
Soldier pile and lagging walls consist of steel piles embedded in concrete caissons, with concrete lagging spanning between the piles. A non-structural concrete fascia can be cast on the outside face of the wall for aesthetic purposes. These walls are the most cost effective when used in areas where the wall is in a cut since they do not require a separate structure for support of excavation. Height can be a concern since these walls require tiebacks when they get tall, which can become expensive and may reduce the cost savings when comparing this wall type to others. Only concrete lagging should be used in permanent soldier pile and lagging walls. While this is more expensive than timber lagging, it will be more durable and have less maintenance problems in the future.

==Avoiding Environmental Impacts==
Often environmental entities request that retaining walls be constructed to avoid impacts to wetlands, forests, floodplains, etc. Before agreeing to this, the benefits of avoiding the environmental feature should be compared to the wall cost and alternative mitigation. Consideration should also be given to whether or not the wall will actually reduce the impacts to the environment. For example, a tall retaining wall may not save a wetland if the wetland will be in the shadow of the wall, causing all the vegetation to die. Similarly, the wall may cut off the flow of water through the wetland, adversely impacting the wetland. It may make more sense to eliminate the wall and provide mitigation for the impacted wetland at another location, especially if the area of the wetland is relatively small.

|}

=See Also=

*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Near Shore and on Shore: Design Vehicles

2016-12-07T19:46:48Z

LLBarry: /* Trailers/Mafis */

{| class="wikitable"
|-
| colspan="3" |
'''Design Vehicles'''

|-
| colspan="3" |
=Primary Guidance=

Design vehicles govern the structural and geometric design of industrial waterfront facilities. The load and geometric vehicle demand is far in excess of highway design standards and thus, constitute a significant cost determinant in both rehabilitation and reconstruction projects. The appropriate design vehicle choice is based on forecasted business needs within the completed project’s service life.

Establish the remaining service life (major rehabilitation) or design service life (reconstruction) for the as-built condition.
For major rehabilitation projects, select design vehicles from the relevant vehicle categories based on an operational forecast window no more than 20 years in the future or the remaining service life, whichever is less. Only those vehicles that are operationally necessary to the forecast business are included.

For reconstruction and new development, select design vehicles from all categories for the mid-point of the design service life (typically 75 years) based on engineering judgment, recommendations from manufacturers, and/or factored existing maximum vehicle loads and geometry. Accommodating all other design vehicles shall be achieved by implementing structural configurations that are optimized to readily permit the future structural retrofits necessary for their use, including crane rail beams (gantry cranes), heavy lift areas (mobile cranes/superload trailers), and rail pits (railcars). Using ballasted one way decks are not only more economical, but they are preferred over flat plate construction to achieve this flexibility.

*Trailers/mafis: capacity determined by customer or max project cargo/superloads in State of MD (currently 1M# ); 100 ton minimum (major rehabilitation)
*Forklifts: loaded container forklift; loaded front axle 125 tons
*Gantry cranes: 40 ton containers (major rehabilitation) and 60 ton containers (reconstruction)
*Mobile harbor cranes: 250 ton minimum; outrigger 225 tons (major rehabilitation)
*Tracked vehicles: ro ro berths only; M80 tank; for pavement surface course selection
*Railcars: Cooper E80 minimum
[[File:IMG_0058.JPG|400px|left]][[File:breakbulk25.jpg|400px|right]]
[[File:breakbulk27.gif|500px|center]]
|-
| colspan="3" |

=Discussion=

==Trailers/Mafis==
Multi-axle trailers transport oversize and overweight project cargo primarily within terminal boundaries. Axle loads of these trailers are typically far in excess of superload highway allowables. Tires may be pneumatic or solid rubber-steel composites. Multi-axle golfhofer trailers typically consist of 8 to 10 axles spaced approximately on 4 ft. centers and allow linking additional 4 to 6 axle units to the base trailer. Mafis are typically 2 or 3 axle trailers with a cargo rating in the range of 100 to 200 tons. A bogie load is the total load on the bogie or all rear axles combined. Bogie loads often govern the design of non-ballasted decks and their framing.

==Forklifts==
Loaded forklift front axle loads can exceed the axle loads imposed by mafis, particularly in facilities where containers are handled. Typical container forklift front axle loads range from 125 tons and higher. Other specialty forklifts may govern design.

==Truck Mounted Cranes==
Truck mounted cranes and mobile harbor cranes deliver extreme loads to decks and substructure elements. Conventional 250 ton truck cranes impose outrigger loads in excess of 200 tons on a 30 inch square foot. 340 ton mobile harbor cranes are some of the largest cranes currently in use worldwide and at capacity impose single outrigger loads in excess of 600 tons.
==Tracked Vehicles==
The live loads imposed by excavators and farm equipment do not typically govern the structural design of waterfront facilities. However, the tracks rapidly and extensively degrade the surface course of the berth and storage lots, particularly at locations where the vehicles turn and pivot. RCC and asphalt-overlaid RCC are the proven surface treatments.

==Railcars==
Rail loads in terminal are limited to a Cooper E80 due to the rating of rail infrastructure outside of the terminals.

==Vessels==
Design vessel minima should be based on vessels currently in use by select business carriers. Vessel particulars for ships currently under development for deployment within typically no more than 5 years.

[[Category:Practical Design Guidance]]

=See Also=
*[[Roadways:_Design_Vehicle| Roadways: Design Vehicle]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Near Shore and on Shore: Design Vehicles

2016-12-07T19:46:16Z

LLBarry: /* Primary Guidance */

{| class="wikitable"
|-
| colspan="3" |
'''Design Vehicles'''

|-
| colspan="3" |
=Primary Guidance=

Design vehicles govern the structural and geometric design of industrial waterfront facilities. The load and geometric vehicle demand is far in excess of highway design standards and thus, constitute a significant cost determinant in both rehabilitation and reconstruction projects. The appropriate design vehicle choice is based on forecasted business needs within the completed project’s service life.

Establish the remaining service life (major rehabilitation) or design service life (reconstruction) for the as-built condition.
For major rehabilitation projects, select design vehicles from the relevant vehicle categories based on an operational forecast window no more than 20 years in the future or the remaining service life, whichever is less. Only those vehicles that are operationally necessary to the forecast business are included.

For reconstruction and new development, select design vehicles from all categories for the mid-point of the design service life (typically 75 years) based on engineering judgment, recommendations from manufacturers, and/or factored existing maximum vehicle loads and geometry. Accommodating all other design vehicles shall be achieved by implementing structural configurations that are optimized to readily permit the future structural retrofits necessary for their use, including crane rail beams (gantry cranes), heavy lift areas (mobile cranes/superload trailers), and rail pits (railcars). Using ballasted one way decks are not only more economical, but they are preferred over flat plate construction to achieve this flexibility.

*Trailers/mafis: capacity determined by customer or max project cargo/superloads in State of MD (currently 1M# ); 100 ton minimum (major rehabilitation)
*Forklifts: loaded container forklift; loaded front axle 125 tons
*Gantry cranes: 40 ton containers (major rehabilitation) and 60 ton containers (reconstruction)
*Mobile harbor cranes: 250 ton minimum; outrigger 225 tons (major rehabilitation)
*Tracked vehicles: ro ro berths only; M80 tank; for pavement surface course selection
*Railcars: Cooper E80 minimum
[[File:IMG_0058.JPG|400px|left]][[File:breakbulk25.jpg|400px|right]]
[[File:breakbulk27.gif|500px|center]]
|-
| colspan="3" |

=Discussion=

==Trailers/Mafis==
Multi-axle trailers transport oversize and overweight project cargo primarily within terminal boundaries. Axle loads of these trailers are typically far in excess of superload highway allowables . Tires may be pneumatic or solid rubber-steel composites. Multi-axle golfhofer trailers typically consist of 8 to 10 axles spaced approximately on 4 ft. centers and allow linking additional 4 to 6 axle units to the base trailer. Mafis are typically 2 or 3 axle trailers with a cargo rating in the range of 100 to 200 tons. A bogie load is the total load on the bogie or all rear axles combined. Bogie loads often govern the design of non-ballasted decks and their framing.

==Forklifts==
Loaded forklift front axle loads can exceed the axle loads imposed by mafis, particularly in facilities where containers are handled. Typical container forklift front axle loads range from 125 tons and higher. Other specialty forklifts may govern design.

==Truck Mounted Cranes==
Truck mounted cranes and mobile harbor cranes deliver extreme loads to decks and substructure elements. Conventional 250 ton truck cranes impose outrigger loads in excess of 200 tons on a 30 inch square foot. 340 ton mobile harbor cranes are some of the largest cranes currently in use worldwide and at capacity impose single outrigger loads in excess of 600 tons.
==Tracked Vehicles==
The live loads imposed by excavators and farm equipment do not typically govern the structural design of waterfront facilities. However, the tracks rapidly and extensively degrade the surface course of the berth and storage lots, particularly at locations where the vehicles turn and pivot. RCC and asphalt-overlaid RCC are the proven surface treatments.

==Railcars==
Rail loads in terminal are limited to a Cooper E80 due to the rating of rail infrastructure outside of the terminals.

==Vessels==
Design vessel minima should be based on vessels currently in use by select business carriers. Vessel particulars for ships currently under development for deployment within typically no more than 5 years.

[[Category:Practical Design Guidance]]

=See Also=
*[[Roadways:_Design_Vehicle| Roadways: Design Vehicle]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Near Shore and on Shore: Dredge Material Containment Facility (DMCF)

2016-12-07T19:11:00Z

LLBarry: /* Primary Guidance */

{| class="wikitable"
|-
| colspan="3" |
'''Dredge Material Containment Facility (DMCF)'''

|-
| colspan="3" |
=Primary Guidance=

*Containment Dike material, geotechnical properties: Unified Soil Classification to be SP or SM , with less than 30 percent passing No. 200 sieve, unless otherwise determined to be acceptable
*Containment Dike material, placement and compaction: Placement in 8 inch maximum loose lifts, compacted to at least 95 percent per standard proctor (ASTM D-1557) , with top 1 ft. of material compacted to at least 98 percent of modified Proctor maximum dry density (ASTM D-1557), unless otherwise determined to be acceptable
*DMCF interior freeboard limit: 2 ft. minimum
*Containment Dike exterior protection: Design armored protection to a minimum of 2 ft. above MHHW
*DMCF holding capacity maintained to accommodate collection of stormwater from 100 year storm event
*Containment Dike, fill and cut slope angles: 3(H):1(V) or flatter, unless otherwise determined to be acceptable
*Containment Dike stability, minimum factor of safety: FS = 1.3, unless otherwise determined to be acceptable
*Crown of Containment Dike (Access Road): 20 ft. minimum width
*DMCF planning to provide adequate capacity available to satisfy the 20 year projected dredging demand to maintain the shipping channels for the Chesapeake Bay and Baltimore Harbor

|-
| colspan="3" |

=Discussion=
[[File:Cox_Creek_Aerial_Final.jpg|200px|right]]
The height and crown width of a dike are primarily dependent on project constraints generally unrelated to stability. Side slopes and materials allocation within the cross section are functions of foundation conditions, material availability, and time available for construction.

For containment dike construction, materials that may be classified as “Silty Sand” with the USCS Classification of “SM” that are derived from weathering of Metamorphic Rocks, which contain significant percentage of Mica, should not be used as fill materials unless otherwise determined to be acceptable.

2 ft. minimum freeboard between the top of containment dikes and top of contained material (dredged material and/or water) must be maintained as capacity for collection of stormwater during significant rain events. DMCF design must take into consideration the provision of adequate storage volume during active inflow of dredged material, as well as for storage of excess water associated with hydraulic placement.

Minimum dike crown width to be maintained to allow for temporary access roadway for construction equipment. The crown of the containment dike is to be designed so as to allow vehicle access for operation of the DMCF as well as for maintenance and contractor activities.

Considering the extended life span of the facility, shoreline protection measures, such as armor stone, are required at the tidal water interface to minimize erosive forces due to currents and wave action.

Cost-Benefit analyses shall be performed for mitigation required for the construction of a DMCF and related facilities.

[[Category:Practical Design Guidance]]

=See Also=
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Near Shore and on Shore: Marine Concrete Piles

2016-11-30T18:07:19Z

LLBarry: /* Pile Driving */

{| class="wikitable"
|-
| colspan="3" |
'''Marine Concrete Piles'''

|-
| colspan="3" |
=Primary Guidance=
Primary Guidance

Test Pile Program
*Unless geotechnical conditions dictate otherwise:
**Specify test pile program for projects where the number of piles to be driven is greater than 10
**Specify a static load test or a statnamic test to confirm ultimate pile capacity for driven piles where the number of piles to be driven is greater than 100
*Specify supplemental embedded EDC instrumentation that provides structural monitoring capability during test pile driving when the driven pile capacity is greater than 100 tons

Pile Driving
*Specify timely post-driving underwater pile inspection by MD registered PE diver
*Specify repair of piles damaged during driving at contractor’s expense
*Reduce allowable driving stresses for marine piles when test pile program or the underwater inspection indicates pile damage is frequently occurring

|-
| colspan="3" |

=Discussion=

==Test Pile Program==
PDA /EDC test pile programs shall be implemented prior to the approval of concrete pile order lengths for larger projects and as subsurface conditions warrant. Static load tests shall be undertaken on very large projects to decrease the required geotechnical factor of safety and reduce pile order lengths.

==Pile Driving==
Using EDC during driving shall be monitored by a geotechnical specialist certified to collect and analyze EDC data. EDC is warranted for driving marine concrete piles in order to prevent pile cracking and damage.

Third-party underwater inspections of all concrete driven piles shall be conducted as soon as possible after driving to identify and scope the repair of driving damage. To the greatest extent possible, allowable tensile driving stresses for concrete piles shall be reduced for in-water piles where damage is detected by EDC gauges, PDA instrumentation (beta<0.90 for more than 10 consecutive blows) and/or underwater inspection.

[[Category:Practical Design Guidance]]

=See Also=

*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Rail: Interlocking

2016-11-30T18:03:30Z

LLBarry: /* Primary Guidance */

{| class="wikitable"
|-
| colspan="3" |
'''Interlocking'''

|-
| colspan="3" |
=Primary Guidance=
*Select universal crossover over double crossover if there are no site constraints
*All special trackwork should be on a horizontal and vertical tangent whenever possible
*Standard Details should be used in order to minimize the spare parts inventory, simplify maintenance, and eliminate manufacturing costs associated with specially made components
|-
| colspan="3" |

=Discussion=
Where an interlocking requires a pair of crossovers, the crossovers should be set in universal crossover configuration for better operations and maintenance. If site constraints preclude universal crossover configuration, a double crossover should be used.

All special trackwork should be on a horizontal and vertical tangent whenever possible to minimize customization manufacturing and installation costs. Replacing an existing interlocking within a curve should consider if realigning the tracks would be more cost effective than manufacturing the special trackwork.

MTA Standard Details should be used for all interlocking special trackwork, including turnouts, single crossovers, double crossovers, and all associated components, in order to minimize the spare parts inventory, simplify maintenance, and eliminate manufacturing costs associated with specially made components.

The distances between switch points of closely spaced turnouts in ladder tracks, universal crossovers, and other special trackwork layouts should allow for the use of standard special trackwork components without modifications. Designers should carefully consider train routings through closely spaced special trackwork and avoid track geometrics that are likely to exceed the capabilities of the vehicle, result in excessive wear, or result in a poor ride quality.

For MARC , special trackwork design should conform to the latest requirements of the Operating Railroad, which owns the track (e.g. Amtrak or CSX). Special trackwork design on portions of track owned by MTA should conform to the latest requirements of the Operating Railroad to which the MTA portion connects.

[[Category:Practical Design Guidance]]

=See Also=
*[[Practical_Design_Implementation_Guidance:_Rail|Rail]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bus: Bus Stop Planning

2016-11-30T18:01:06Z

LLBarry: /* Bus Stop Locations */

{| class="wikitable"
|-
| colspan="3" |
'''Bus Stop Planning'''

|-
| colspan="3" |
=Primary Guidance=
*Bus stops locations should be evaluated based on the following factors
*Bus stops are usually placed at major intersections, transfer points, and major passenger generators
*The minimum distance between bus stops varies according to the service type, adjacent land use, population/employment density, and topography

|-
| colspan="3" |

=Discussion=

==Bus Stop Locations==
Providing bus stops on new or existing routes requires additional capital and operating costs for each stop and increases travel time for customers. Therefore, planning bus stop locations should consider the following factors to determine if a bus stop is warranted:
*Improves service quality and reliability
*Maximizes access to high-frequency transit
*Strengthens intermodal connections
*Aligns with existing or emerging employment, education and other community related services
*ADA accessibility between the service point and the passenger destinations / generators

==Bus Stop Spacing and Positioning==
Bus stops are spaced to balance accessibility reliability. Close spacing of bus stops shortens walk distance for passengers, but increases transit trip time due to more stops and starts by the buses. Bus stops are usually placed at major intersections, transfer points, and major passenger generators.

Unless dictated by the Bus Stop Locations factors above, the minimum distance between bus stops varies according to the service type:
*Closer bus stop spacing (1/4 mile or less) is appropriate where adjacent land uses and population/employment densities warrant
*In lower density residential and commercial areas, bus stop spacing should be no greater than ½ mile distance between stops
*Pedestrian elements such as sidewalks, curb ramps, and lighting may dictate bus stop spacing along a corridor
*Topography as stops may be placed closer together uphill versus downhill
*For suburban-suburban or suburban-urban express bus routes, the only bus stop spacing needed is in the distribution portion of the route. Distribution stops should generally be spaced about every 2 to 3 blocks in major activity centers or where demand warrants (major ridership generators).

[[Category:Practical Design Guidance]]

=See Also=
*[[Bus: Bus Stop Design|Bus Stop Design]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bus: Bus Stop Planning

2016-11-30T18:00:23Z

LLBarry: /* Primary Guidance */

{| class="wikitable"
|-
| colspan="3" |
'''Bus Stop Planning'''

|-
| colspan="3" |
=Primary Guidance=
*Bus stops locations should be evaluated based on the following factors
*Bus stops are usually placed at major intersections, transfer points, and major passenger generators
*The minimum distance between bus stops varies according to the service type, adjacent land use, population/employment density, and topography

|-
| colspan="3" |

=Discussion=

==Bus Stop Locations==
Providing bus stops on new or existing routes requires additional capital and operating costs for each stop and increases travel time for cusstomers. Therefore, planning bus stop locations should consider the following factors to determine if a bus stop is warranted:
*Improves service quality and reliability
*Maximizes access to high-frequency transit
*Strengthens intermodal connections
*Aligns with existing or emerging employment, education and other community related services
*ADA accessibility between the service point and the passenger destinations / generators

==Bus Stop Spacing and Positioning==
Bus stops are spaced to balance accessibility reliability. Close spacing of bus stops shortens walk distance for passengers, but increases transit trip time due to more stops and starts by the buses. Bus stops are usually placed at major intersections, transfer points, and major passenger generators.

Unless dictated by the Bus Stop Locations factors above, the minimum distance between bus stops varies according to the service type:
*Closer bus stop spacing (1/4 mile or less) is appropriate where adjacent land uses and population/employment densities warrant
*In lower density residential and commercial areas, bus stop spacing should be no greater than ½ mile distance between stops
*Pedestrian elements such as sidewalks, curb ramps, and lighting may dictate bus stop spacing along a corridor
*Topography as stops may be placed closer together uphill versus downhill
*For suburban-suburban or suburban-urban express bus routes, the only bus stop spacing needed is in the distribution portion of the route. Distribution stops should generally be spaced about every 2 to 3 blocks in major activity centers or where demand warrants (major ridership generators).

[[Category:Practical Design Guidance]]

=See Also=
*[[Bus: Bus Stop Design|Bus Stop Design]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bus: Bus Stop Design

2016-11-30T17:59:20Z

LLBarry: /* Bus Stops at Park and Ride or Transfer Facilities */

{| class="wikitable"
|-
| colspan="3" |
'''Bus Stop Design'''

|-
| colspan="3" |
=Primary Guidance=
*At minimum, bus stops shall be designed to meet Americans with Disabilities Act (ADA) Accessibility Guidelines
*Bus stops typically include an ADA-compliant passenger boarding area and signage as well as amenities such as shelters, benches, and trash receptacles
*Concrete bus pads should be constructed based on bus service frequency and transit vehicle type used
*Where bus stops are a part of a park and ride or transfer facility, site access and on-site traffic for buses should be separated from automobile traffic to the greatest extent feasible

|-
| colspan="3" |

=Discussion=

Bus stops should be designed to be distinct and easily identifiable to customers. At minimum, bus stops shall be designed to meet Americans with Disabilities Act Accessibility Guidelines.

=Bus Stop Facilities=

===Passenger Boarding Area and Signage===
At a minimum, a bus stop must meet ADA Accessibility Guidelines and should have standard signing to identify the bus stop location and the routes served. Streetscape improvements such as curb ramps and improvement of longitudinal/cross slopes should be considered to improve access for people with disabilities in accordance with the ADA. Landing pads are provided at stops where the curb service point is separated from the sidewalk by a grass strip in order to accommodate service for customers using wheelchairs.

===Bus Shelters===
Bus shelters should be considered at locations with substantial boardings where space permits without impeding sidewalk use and where service quality would be improved. Basic shelter requirements would be modularity, accessibility, vandal resistance, low maintenance, and visual transparency for safety.

===Bus Pads===
Bus stops should have a concrete bus pad on roadway that is typically 90 ft. long and as wide as the bus lane. Roadway pavement or bus pads for the bus stop should be evaluated for suitability for the anticipated frequency of bus traffic and to meet requirements of the local jurisdictions. Reinforced concrete pavement slabs should be considered to prevent pavement deterioration due to bus loads and the effects of braking. In situations with low frequency bus service and in consultation with the local jurisdiction, the provision of a concrete pad may be waived.

===Bus Stops at Park and Ride or Transfer Facilities===

Where bus stops are a part of a park and ride or transfer facility, site access and on-site traffic for busses should be separated from automobile traffic to the greatest extent feasible.

Bus stops located at park and ride or other transfer facilities should incorporate enhanced features that promote improvement in service quality and strengthen connections to other transportation modes. These enhanced features include:
*Enhanced Signage for wayfinding and transfer information
*Real Time Information Signage
*Bicycle Storage
**'''NOTE''': At BWI, no bike storage lockers are to be placed on the premises of the Airport Terminal.
Shelters or Canopy:
*Ticket Vending Machines
*Enhanced Lighting/Ornamental Fencing for increased safety and security
*CCTV
*Trash Receptacles
*Operator Restrooms
[[Category:Practical Design Guidance]]

=See Also=

*[[Bus: Bus Stop Planning|Bus Stop Planning]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bus: Bus Stop Design

2016-11-30T17:58:40Z

LLBarry: /* Bus Stops at Park and Ride or Transfer Facilities */

{| class="wikitable"
|-
| colspan="3" |
'''Bus Stop Design'''

|-
| colspan="3" |
=Primary Guidance=
*At minimum, bus stops shall be designed to meet Americans with Disabilities Act (ADA) Accessibility Guidelines
*Bus stops typically include an ADA-compliant passenger boarding area and signage as well as amenities such as shelters, benches, and trash receptacles
*Concrete bus pads should be constructed based on bus service frequency and transit vehicle type used
*Where bus stops are a part of a park and ride or transfer facility, site access and on-site traffic for buses should be separated from automobile traffic to the greatest extent feasible

|-
| colspan="3" |

=Discussion=

Bus stops should be designed to be distinct and easily identifiable to customers. At minimum, bus stops shall be designed to meet Americans with Disabilities Act Accessibility Guidelines.

=Bus Stop Facilities=

===Passenger Boarding Area and Signage===
At a minimum, a bus stop must meet ADA Accessibility Guidelines and should have standard signing to identify the bus stop location and the routes served. Streetscape improvements such as curb ramps and improvement of longitudinal/cross slopes should be considered to improve access for people with disabilities in accordance with the ADA. Landing pads are provided at stops where the curb service point is separated from the sidewalk by a grass strip in order to accommodate service for customers using wheelchairs.

===Bus Shelters===
Bus shelters should be considered at locations with substantial boardings where space permits without impeding sidewalk use and where service quality would be improved. Basic shelter requirements would be modularity, accessibility, vandal resistance, low maintenance, and visual transparency for safety.

===Bus Pads===
Bus stops should have a concrete bus pad on roadway that is typically 90 ft. long and as wide as the bus lane. Roadway pavement or bus pads for the bus stop should be evaluated for suitability for the anticipated frequency of bus traffic and to meet requirements of the local jurisdictions. Reinforced concrete pavement slabs should be considered to prevent pavement deterioration due to bus loads and the effects of braking. In situations with low frequency bus service and in consultation with the local jurisdiction, the provision of a concrete pad may be waived.

===Bus Stops at Park and Ride or Transfer Facilities===

Where bus stops are a part of a park and ride or transfer facility, site access and on-site traffic for busses should be separated from automobile traffic to the greatest extent feasible.

Bus stops located at park and ride or other transfer facilities should incorporate enhanced features that promote improvement in service quality and strengthen connections to other transportation modes. These enhanced features include:
*Enhanced Signage for wayfinding and transfer information
*Real Time Information Signage
*Bicycle Storage
**'''NOTE''': At BWI, no bike storage lockers are to be placed on the premises of the Airport Terminal.
Shelters or Canopy
*Ticket Vending Machines
*Enhanced Lighting/Ornamental Fencing for increased safety and security
*CCTV
*Trash Receptacles
*Operator Restrooms
[[Category:Practical Design Guidance]]

=See Also=

*[[Bus: Bus Stop Planning|Bus Stop Planning]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bus: Bus Stop Design

2016-11-30T17:57:32Z

LLBarry: /* Bus Pads */

{| class="wikitable"
|-
| colspan="3" |
'''Bus Stop Design'''

|-
| colspan="3" |
=Primary Guidance=
*At minimum, bus stops shall be designed to meet Americans with Disabilities Act (ADA) Accessibility Guidelines
*Bus stops typically include an ADA-compliant passenger boarding area and signage as well as amenities such as shelters, benches, and trash receptacles
*Concrete bus pads should be constructed based on bus service frequency and transit vehicle type used
*Where bus stops are a part of a park and ride or transfer facility, site access and on-site traffic for buses should be separated from automobile traffic to the greatest extent feasible

|-
| colspan="3" |

=Discussion=

Bus stops should be designed to be distinct and easily identifiable to customers. At minimum, bus stops shall be designed to meet Americans with Disabilities Act Accessibility Guidelines.

=Bus Stop Facilities=

===Passenger Boarding Area and Signage===
At a minimum, a bus stop must meet ADA Accessibility Guidelines and should have standard signing to identify the bus stop location and the routes served. Streetscape improvements such as curb ramps and improvement of longitudinal/cross slopes should be considered to improve access for people with disabilities in accordance with the ADA. Landing pads are provided at stops where the curb service point is separated from the sidewalk by a grass strip in order to accommodate service for customers using wheelchairs.

===Bus Shelters===
Bus shelters should be considered at locations with substantial boardings where space permits without impeding sidewalk use and where service quality would be improved. Basic shelter requirements would be modularity, accessibility, vandal resistance, low maintenance, and visual transparency for safety.

===Bus Pads===
Bus stops should have a concrete bus pad on roadway that is typically 90 ft. long and as wide as the bus lane. Roadway pavement or bus pads for the bus stop should be evaluated for suitability for the anticipated frequency of bus traffic and to meet requirements of the local jurisdictions. Reinforced concrete pavement slabs should be considered to prevent pavement deterioration due to bus loads and the effects of braking. In situations with low frequency bus service and in consultation with the local jurisdiction, the provision of a concrete pad may be waived.

===Bus Stops at Park and Ride or Transfer Facilities===

Where bus stops are a part of a park and ride or transfer facility, site access and on-site traffic for busses should be separated from automobile traffic to the greatest extent feasible.

Bus stops located at park and ride or other transfer facilities should incorporate enhanced features that promote improvement in service quality and strengthen connections to other transportation modes. These enhanced features include:
*Enhanced Signage for wayfinding and transfer information
*Real Time Information Signage
*Bicycle Storage
**'''NOTE''': At BWI, No bike storage lockers are to be placed on the premises of the Airport Terminal.
Shelters or Canopy
*Ticket Vending Machines
*Enhanced Lighting/Ornamental Fencing for increased safety and security
*CCTV
*Trash Receptacles
*Operator Restrooms
[[Category:Practical Design Guidance]]

=See Also=

*[[Bus: Bus Stop Planning|Bus Stop Planning]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]

Bus: Bus Stop Design

2016-11-30T17:56:40Z

LLBarry: /* Passenger Boarding Area and Signage */

{| class="wikitable"
|-
| colspan="3" |
'''Bus Stop Design'''

|-
| colspan="3" |
=Primary Guidance=
*At minimum, bus stops shall be designed to meet Americans with Disabilities Act (ADA) Accessibility Guidelines
*Bus stops typically include an ADA-compliant passenger boarding area and signage as well as amenities such as shelters, benches, and trash receptacles
*Concrete bus pads should be constructed based on bus service frequency and transit vehicle type used
*Where bus stops are a part of a park and ride or transfer facility, site access and on-site traffic for buses should be separated from automobile traffic to the greatest extent feasible

|-
| colspan="3" |

=Discussion=

Bus stops should be designed to be distinct and easily identifiable to customers. At minimum, bus stops shall be designed to meet Americans with Disabilities Act Accessibility Guidelines.

=Bus Stop Facilities=

===Passenger Boarding Area and Signage===
At a minimum, a bus stop must meet ADA Accessibility Guidelines and should have standard signing to identify the bus stop location and the routes served. Streetscape improvements such as curb ramps and improvement of longitudinal/cross slopes should be considered to improve access for people with disabilities in accordance with the ADA. Landing pads are provided at stops where the curb service point is separated from the sidewalk by a grass strip in order to accommodate service for customers using wheelchairs.

===Bus Shelters===
Bus shelters should be considered at locations with substantial boardings where space permits without impeding sidewalk use and where service quality would be improved. Basic shelter requirements would be modularity, accessibility, vandal resistance, low maintenance, and visual transparency for safety.

===Bus Pads===
Bus stops should have a concrete bus pad on roadway that is typically 90 ft. long and as wide as the bus lane. Roadway pavement or bus pads for the bus stop should be evaluated for suitability for the anticipated frequency of bus traffic and to meet requirements of the local jurisdictions . Reinforced concrete pavement slabs should be considered to prevent pavement deterioration due to bus loads and the effects of braking. In situations with low frequency bus service and in consultation with the local jurisdiction, the provision of a concrete pad may be waived.

===Bus Stops at Park and Ride or Transfer Facilities===

Where bus stops are a part of a park and ride or transfer facility, site access and on-site traffic for busses should be separated from automobile traffic to the greatest extent feasible.

Bus stops located at park and ride or other transfer facilities should incorporate enhanced features that promote improvement in service quality and strengthen connections to other transportation modes. These enhanced features include:
*Enhanced Signage for wayfinding and transfer information
*Real Time Information Signage
*Bicycle Storage
**'''NOTE''': At BWI, No bike storage lockers are to be placed on the premises of the Airport Terminal.
Shelters or Canopy
*Ticket Vending Machines
*Enhanced Lighting/Ornamental Fencing for increased safety and security
*CCTV
*Trash Receptacles
*Operator Restrooms
[[Category:Practical Design Guidance]]

=See Also=

*[[Bus: Bus Stop Planning|Bus Stop Planning]]
*[[Practical Design Implementation Guidance|Practical Design Implementation Guidance]]