VALIDATION OF SELECTED SIGNALIZED INTERSECTION CAPACITY FACTORS FOR SMALL URBAN AREAS IN ILLINOIS. FINAL REPORT

The purpose of this study was to validate the saturation flow rates and progression factors in the 1985 Highway Capacity Manual in small urban areas in Illinois. It was found that the use of an ideal saturation flow rate of 1,800 vphgl is reasonable for small urban areas, as opposed to the observed 2,000 vphgl value observed in the Chicago Metropolitan area. Progression factors were found to be dependent on the proportion of platoon arrivals in green, as in the Highway Capacity Manual, but not on the degree of saturation. This is in line with recent recommendations of NCHRP project 3-28C in which progression factors are estimated strictly from arrivals in green and green splits. Overall, the study found the 1985 Highway Capacity Manual model for signalized intersections gave substantially better results in small urban areas in Illinois compared to Chicago.