Center for Traffic Simulation Studies

The U.S. Highway Capacity Manual (HCM)presents a procedure for estimating signalized intersection control delay which is used to determine level of service (LOS) and to evaluate intersection performance. The HCM is extensively used by traffic engineers. However, it is intended as an off-line decision support tool for planning and design. To meet user requirements of advanced transportation management systems (ATMS), new LOS criteria are required for real-time intersection analysis. The objective of this research was to demonstrate a technique for development of such LOS criteria. The study uses a new measure of effectiveness, called re-identification delay (RD) derived from analysis of vehicle inductive signatures and reidentification of vehicles traveling through a major signalized intersection in the City of Irvine, California. This paper addresses two main issues related to real-time LOS criteria. The first is how to determine the threshold values partitioning the LOS categories. To provide reliable real-time traffic information, the threshold values should be decided so that RDs within the same LOS category represent similar traffic conditions. Conversely,RDs in different LOS categories should represent dissimilar traffic conditions. The second issue concerns the aggregation interval to use for RD in deriving LOS categories. An investigation of both fixed and cycle-based aggregation intervals was conducted. Several clustering techniques were then used to derive LOS categories. These included K-means, fuzzy, and self-organizing map (SOM) approaches. The resulting real-time LOS criteria are presented. The procedures used in this study are readily transferable to other signalized intersections for the derivation of real-time LOS.