Bridge Size and Clearance Time of Single‐Point Urban Interchange

Abstract

The single‐point urban interchange (SPUI) is a relatively new type of diamond interchange. Its reported advantages are improved operational efficiency, improved safety, and reduced right‐of‐way requirements as compared to other interchange forms. This paper focuses on the efficiency and right‐of‐way requirement issues by examining the relationships among the various SPUI design elements. In particular, constraints placed on the SPUI geometry by the bridge‐abutment locations and offset left‐turn paths made it possible to develop a geometric model relating turn radius, cross‐section width, number and width of turn lanes, and skew angle to bridge length and clearance path length. A sensitivity analysis using the geometric model developed in this paper indicates that skew angle, cross‐road median width, and ramp‐major road clearance distance have a significant effect on the length of the bridge and the duration of the all‐red clearance interval. An illustrative application of the model indicates that it can be used to develop relationships among SPUI design elements that yield the most cost‐effective design.