Roadways: Vertical Alignment

Vertical Alignment

Primary Guidance Vertical Alignments shall be designed using the anticipated posted speed as the design speed Vertical Alignments shall be designed to meet the existing topography when practical and balance earthwork which will minimize excessive needs for fill material or hauling of extra cut material. Vertical Alignments on high speed facilities, such as Interstates and arterials should be designed with a maximum vertical grade between 3-7% based on the design speed, context, and terrain of the roadway Vertical Alignments for 3R projects should be evaluated to determine if there is crash or maintenance history to suggest the need for modification. If no crash or maintenance history suggests a condition warranting a change to the existing alignment, the existing alignment should remain

Discussion The operational characteristics of a roadway are directly influenced by the horizontal and vertical alignments. The designer should coordinate both horizontal and vertical alignments while under development. There are many different factors that the designer needs to consider when developing the alignments. Some of the most important to be considered are design speed, existing topography, and context of the road. For long corridor alignments that may transition from rural to urban zones and vise-versa, the designer should consider the changing context of the road and not design the corridor to one context or one design speed. This will result in an alignment that may transition if there is a need to reduce speeds through urban sections. In the areas of transition, the designer should pick an appropriate design speed along the alignment in the transition zone to help reduce prevailing speeds as the driver approaches the urban zone. This approach will allow the designer to use more flexible design techniques and not over design sections not meeting the context of the facility. The designer should make every effort to follow the topography to minimize footprint of the roadway and impacts associated with grading in high fills or deep cuts. Where the roadway crosses water, existing or proposed roadways or railways, the designer should coordinate with the appropriate office or Agency to identify the appropriate minimum and maximum allowable crossing heights and widths of the crossing. Maximum grades for Interstate (lower maximum grade for higher design speed): Level – 3-4 Rolling – 4-5 Mountainous – 5-6 Maximum grade for high speed Arterial (lower maximum grade for higher design speed): Level – 3-5 Rolling – 4-6 Mountainous – 5-7

See Also

• Bridge: Horizontal and Vertical Alignment