Technique for Comparing Operation of Alternative Interchange Types

Interchanges have been the focus of several recent studies that attempted to identify the conditions in which one interchange type is more efficient than another. However, the guidance offered is of such a general nature that it is difficult to apply with confidence in a specific situation. The objective of this study was to describe an interchange evaluation technique that is of sufficient precision to facilitate interchange-type selection or planning-level evaluations of interchange performance. This technique was based on the use of characteristic curves that define the relationship between interchange delay and the sum-of-critical-flow-ratios. This sum represents a unique parameter that combines the effect of signal phase sequence, traffic volume, number of lanes, and saturation flow rate. A family of characteristic curves was developed and used to illustrate the interchange evaluation technique. The curves describe the relationship between delay and the sum-of-critical-flow-ratios for the single-point urban interchange (SPUI) and the tight urban diamond interchange (TUDI), both serving frontage-road systems. For the range of conditions considered, it was concluded that the TUDI will generally operate with less delay than the SPUI.