A microscopic inspection of the operational aspects of urban interchanges

The Michigan Department of Transportation (MDOT) is considering the much needed rehabilitation and upgrading of many interchanges found in urban environments. Thus, Michigan State University (MSU) undertook an effort to evaluate the appropriateness of an urban interchange geometric configuration, the Single Point Urban Interchange (SPUI), as an alternative design to those presently used by MDOT. In particular, the Michigan Urban Diamond Interchange (MUDI) and the traditional diamond were investigated.; A field review was conducted to collect information about the geometric design, signal operation, pedestrian control and pavement markings of SPUIs, as none currently exist in Michigan. The field review showed that the design and operation of SPUIs vary greatly from state to state. Thus, the SPUI and MUDI designs were computer modeled to facilitate a comparison of their respective operational characteristics. A traditional diamond was also modeled to generate a frame of reference.; The results showed that the SPUI operation is adversely affected with the addition of frontage roads. MUDI operation, in most situations, is superior to that of either a SPUI and diamond interchange configuration. Also, there was less migration of delay to downstream intersections with a MUDI configuration than with either a SPUI or diamond. Finally, MUDI operation, in most situations, is insensitive to the proximity of the closest downstream node, while the SPUI operation is sensitive.