U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
NCHRP Report 500 / Volume 12: A Guide for Reducing Collisions at Signalized Intersections
Signalized intersections with safety problems related to sight distance that cannot be addressed with less expensive methods.
If other less expensive methods cannot be used or are ineffective, horizontal or vertical (or both) realignment of approaches may be a solution. Realigning both of the minor road approaches so that they intersect the major road at a different location, or a different angle, can help address horizontal sight distance issues.
This is a high-cost, longer-term treatment for the intersection, but if completed according to applicable design policy, it should help alleviate crashes related to sight distance. The AASHTO Policy on Geometric Design of Highways and Streets contains sight distance guidelines, and these guidelines should be considered when revising intersection approach geometry.
An intersection leg can be closed or can be made one-way away from the intersection in order to address sight distance issues related to that particular leg. Intersection relocation and closure, elimination of intersection skew, and offsetting of left-turn lanes are all strategies that involve improvements to approach alignment to improve sight distance.
There are significant right-of-way and property access issues involved in this strategy, and public information campaigns are vital to the success of the intersection improvements.
Owners of properties where access would be reduced, especially owners of commercial operations, may oppose this strategy. Thus, careful evaluation of the potential impacts of proposed improvements is needed to avoid or minimize such problems.
This strategy requires a long implementation time. At least one year is necessary to work out the details of intersection approach realignment and to communicate the plan to affected businesses owners and residents. Where relocation requires right-of-way acquisition and/or demolition of existing structures, an extensive project development process of up to four years may be required.
The costs to change the horizontal or vertical alignment of an intersection approach are usually high. Furthermore, additional right-of-way will generally need to be acquired.
PROVEN: Implementing any of these strategies should improve safety at signalized intersections. More research is needed to better quantify estimates of crash reduction for these countermeasures.
This strategy can be used in conjunction with other strategies for improving safety at signalized intersections.
For more details on this and other countermeasures: http://safety.transportation.org
For more information contact:
FHWA Office of Safety Design
E71, 1200 New Jersey Avenue SE
Washington, D.C. 20590
FHWA Resource Center – Safety and Design Team
19900 Governor's Drive, Suite 301
Olympia Fields, IL 60461