Roadways: Vertical Alignment

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Vertical Alignment

Primary Guidance

  • Vertical Alignments shall be designed:
    • Using the anticipated posted speed as the design speed
    • 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 to 7 percent based on the design speed, context, and terrain of the roadway
  • Vertical Alignments for 3R3R stands for resurfacing, restoration, and rehabilitation projects. 3R projects typically involve pavement improvement work (short of full-depth replacement) and targeted safety improvements. 3R projects generally involve retention of the existing three-dimensional alignment. 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 roadway characteristics are directly influenced by the horizontal and vertical alignments. The designer should coordinate both while under development. There are many different factors to consider when developing the alignments, particularly design speed, existing topography, and context of the road.

For long corridor alignments that may transition from rural to urban zones and vise-versa, consider the changing context of the road rather than designing 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, pick an appropriate design speed along the transition zone alignment 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 overdesign sections not meeting the context of the facility.

Make every effort to follow the topography to minimize the roadway footprint and impacts associated with grading in high fills or deep cuts. Where the roadway crosses water, existing or proposed roadways or railways, 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 to 4 Rolling – 4 to 5 Mountainous – 5 to 6

Maximum grade for high speed Arterial (lower maximum grade for higher design speed): Level – 3 to 5 Rolling – 4 to 6 Mountainous – 5 to 7

See Also