New alternative intersection and interchange designs – including Diverging Diamond Interchanges (DDI), Displaced Left-Turn (DLT) or Continuous Flow Intersections (CFI), Restricted Crossing U-Turn (RCUT) intersections, Median U-Turn (MUT) intersections, Quadrant Roadway (QR) intersections – are being built in the United States. 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, cyclists, and pedestrians as well as better accommodations for pedestrians and bicyclists, including pedestrians with disabilities.
A central concern with alternative intersections is how to provide information to pedestrians, bicyclists, and drivers about the direction of car traffic, pedestrian crossing, and bicycle facilities particularly when those new intersection designs feature unfamiliar traffic flows and patterns. The concern is acute for visually impaired pedestrians, who require information about the alignment of crosswalks, signal controls, crossing times, direction of traffic, and direction through islands. Consistency in how information is provided is important as well; for example, various types of paths and lane markings are being used for bicyclists, with little information about the advantages and disadvantages of different strategies.
The objective of this research is to develop a guide for transportation practitioners to improve and integrate pedestrian and bicycle safety considerations at alternative intersections and interchanges (AII) through planning, design, and operational treatments that (1) identifies and evaluates current practices, and emerging technologies and trends, in the U.S. and internationally; (2) describes current best practices for measuring the effectiveness of such AII treatments; (3) evaluates the safety and operational outcomes of specific AII treatments; and (4) identifies and ranks treatments for typical types of projects. The primary focus of the research is roadway functional classifications of collector and above.
The approaches to evaluate pedestrian and bicycle treatments can be separate, but implementation of the treatments should be coordinated. The guide should address a broad range of issues related to improved pedestrian and bicycle safety at AII such as, but not limited to, the following:
- Describing new and emerging AII designs (e.g., Diverging Diamond Interchanges (DDI), Displaced Left-Turn (DLT) or Continuous Flow (CFI) intersections, Restricted Crossing U-Turn (RCUT) intersections, Median U-Turn (MUT) intersections, Quadrant Roadway (QR) intersections) and evaluating their impacts on pedestrians and bicyclists;
- Documenting domestic and international best practices for integrating pedestrian and bicyclist movements into AII designs;
- For each AII type, documenting key considerations such as wayfinding, accommodation for pedestrians with disabilities (including visually and hearing impaired), delay for pedestrians and cyclists, and safety for pedestrians and cyclists;
- Documenting benefits and trade-offs of pedestrian and bicycle AII design and operational treatments;
- Developing a design and operational matrix for evaluating, selecting, and incorporating pedestrian and cyclist safety considerations for AII treatments;
- Designing and implementing one or more approaches (e.g., simulation, case studies, modeling, scenario planning) to evaluate the impacts of AII on pedestrian and bicyclist behavior; and
- Providing a foundation for future data collection to produce Crash Modification Factors (CMFs).
While the guide should be directly applicable to most situations, it should also outline decision-making processes and criteria that would assist agencies in identifying flexible solutions.
Note: The research is underway.