Over the past decade, the Federal Highway Administration (FHWA) has conducted and developed extensive research, workshops, technical briefs, and other outreach materials about alternative intersections/interchanges. These research efforts and publications have increased interest and rapid adoption of alternative geometric designs across the United States. Of the many alternative intersection/interchange designs, stakeholders showed significant interest in these four: Double Crossover Diamond (DCD) interchange (or Diverging Diamond Interchange (DDI)). Displaced Left Turn (DLT) intersection. Median U-Turn (MUT) intersection. Restricted Crossing U-Turn (RCUT) intersection. Most existing analysis tools supporting the adoption of alternative intersections/interchanges involve the use of complex microscopic simulations that are expensive and time consuming. The Highway Capacity Manual (HCM) and the Highway Capacity Software (HCS) are widely used analytical tools that assess the quality of service for conventional intersections and interchanges. However, they do not assess any of the alternative designs considered in this project.To support the increased exposure and interest in these designs, FHWA is conducting activities to integrate alternative intersection/interchange guidance into the HCM and HCS. This will help expand the portfolio of design alternatives contained in the HCM and enable a side-by-side assessment of their operations in contrast to traditional designs.
To develop Highway Capacity Manual (HCM) analysis procedures for evaluating capacity and quality of service of the Double Crossover Diamond (DCD) interchange (aka, Diverging Diamond Interchange (DDI), Displaced Left Turn (DLT) intersection, Median U-Turn (MUT) intersection, and Restricted Crossing U-turn (RCUT) intersection). These procedures or guides should include extensions of HCM methods to address gaps in the HCM relevant to the operations of these advanced intersection types.