Alternative Intersection and Interchange (AII) designs are those which provide an innovative approach to the geometric or control features which may improve operations and/or safety for different road users. In 2010, the U.S. Federal Highway Administration (FHWA) published the first edition of "Alternative Intersections/Interchanges: Informational Report" (AIIR), which provided information on six alternative treatments including: displaced left turn (DLT) intersections, restricted crossing U-turn (RCUT) intersections, median U turn (MUT) intersections, quadrant roadway (QR) intersections, double crossover diamond (DCD) interchanges, and DLT interchanges. For each treatment, the report provides detailed information in a standardized format, including salient geometric design features, operational and safety issues, access management, costs, construction sequencing, environmental benefits, and applicability.
This report has been used by various agencies and has proven to be a valuable resource for planning and designing AIIs; however, there are still unconventional design concepts that have not been fully explored and some of the current ones could use updates. During the past decade, there have been an increasing number of AIIs installed in the United States, and additional new AII designs that are not documented in the AIIR first edition have emerged since 2010. Examples of these designs include Reverse RCUTs, Partial Median U-turns, and Grade-Separated Alternative Intersections. These new AII designs may involve different traffic patterns, which may introduce confusion and create new safety hazards for drivers.
This research will provide a state-of-the-practice literature review and expert interviews on AII designs, draft an annotated outline for the AIIR second edition, and provide supplemental tools to help planners and engineers select site-specific AII's during the project planning and design process.
