Change Intervals and Lost Time at Single‐Point Urban Interchanges

Abstract

The single‐point urban interchange (SPUI) is a relatively new type of diamond interchange. It is claimed to offer improved operational efficiency, improved safety, and reduced right‐of‐way requirements over other interchange forms. This paper addresses the area of operational efficiency by focusing on the SPUI's change interval requirements and the implications of these requirements on the amount of lost time incurred at the end of the signal phase. Values of end lost time are calculated for the SPUI and compared to those of a typical, high‐type at‐grade intersection (AGI). End lost time calculations for the SPUIs and AGIs indicated that the SPUI signal phases have longer end lost times than do the AGI phases. In particular, the SPUI through phase was found to have 1.5‐2.5 sec more end lost time than the AGI through phase. Similarly, the SPUI left‐turn phase was found to have about 1.0‐2.0 sec more end lost time than the AGI left‐turn phase.