Levels of service for signalized intersection approaches in Chapter 9 of the 1985 Highway Capacity Manual (HCM), published as TRB Special Report 209, are based on stopped delay as computed from the cycle length, G/C ratio, v/c ratio, saturation flow, and quality of progression. Quality of signal progression has a major influence on stopped delay, as evidenced by the progression adjustment factors (PF) in Table 9-13 of Chapter 9 varying from 0.40 to 1.85. However, the adjustment factors were based on limited data. Field data, supplemented by simulation, were needed to verify the variations in delay resulting from changes in the quality of progression.

The product of this research was a calibrated set of progression adjustment factors in the form of a revised version of Table 9-13 (TRB Special Report 209) and a replacement delay adjustment technique. This product is suitable for application to the general stopped delay model of Chapter 9 and to the urban arterials procedure in Chapter 11 of the HCM.

All research has been completed. The results have been incorporated into the latest version of the Highway Capacity Manual. The final report has been published as NCHRP Report 339, "Effects of the Quality of Traffic Signal Progression on Delay."