Alternative Intersections and Interchanges (A.I.I.s) are designs that improve operations and safety for motorized traffic by strategically adjusting the geometric features at a given location, working on the general principle of redistributing motor vehicle demand at an intersection in an attempt to limit the need to add capacity with new lanes to improve traffic flow.
The TRB National Cooperative Highway Research Program's NCHRP Research Report 948: Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges provides specific guidance for four common A.I.I.s: Diverging Diamond Interchange (DDI), Restricted Crossing U-Turn (RCUT), Median U-Turn (MUT), and Displaced Left-Turn (DLT).
These designs may involve reversing traffic lanes from their traditional directions, which may introduce confusion and create safety issues for pedestrians and bicyclists. In addition, pedestrian paths and bicycle facilities may cross through islands or take different routes than expected. These new designs are likely to require additional information for drivers, bicyclists, and pedestrians as well as better accommodations for pedestrians and bicyclists, including pedestrians with disabilities.
NCHRP 20-44(35) is the implementation project for NCHRP Research Report 948. The implementation project's objective is to share and disseminate the research results with public agencies and provide hands-on technology transfer assistance to these agencies. Find project outcomes, including webinars and training materials, on the implementation project page.
National Academies of Sciences, Engineering, and Medicine. 2021. Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges. Washington, DC: The National Academies Press. https://doi.org/10.17226/26072.
|Chapter 1 - Introduction||1-10|
|Chapter 2 - Pedestrians||11-26|
|Chapter 3 - Bicycles||27-42|
|Chapter 4 - Assessment||43-92|
|Chapter 5 - Generalized Design Treatments||93-116|
|Chapter 6 - Median U-Turn (MUT) Intersections||117-136|
|Chapter 7 - Restricted Crossing U-Turn (RCUT) Intersections||137-160|
|Chapter 8 - Displaced Left-Turn (DLT) Intersections||161-186|
|Chapter 9 - Diverging Diamond Interchanges (DDIs)||187-212|
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