Evaluation of Traditional and Nontraditional Interchange Treatments to Preserve Service Life of Narrow Over-and Underpass Roadways

Abstract

This paper presents key findings from an evaluation of the potential of traditional and nontraditional interchange treatments to postpone or eliminate the need for overpass or underpass widening. The study compares the relative performance of five traditional and five nontraditional interchange treatments at two common sites. The treatments included traditional widening, single-point urban interchange, tight urban diamond, Texas three-phase (TX-3), Texas four-phase (TX-4), tight urban diamond with reversing lanes, double roundabout, diverging diamond, median U-turn, and superstreet. Although the performance of each treatment will always vary with site-specific geometric and volume characteristics, some general trends were apparent across sites. The TX-3 and TX-4 treatments were found to be excellent short- to medium-term performers, especially considering their low cost for implementation. The tight urban diamond with reversing lanes and the diverging diamond treatments were found to be reasonable medium- to long-term performers, although each was better suited to particular traffic patterns. The traditional widening and single-point urban interchange treatments were the best long-term performers, with the single-point urban interchange providing the best performance overall.