Overflow Delay Estimation for a Simple Intersection with Fully Actuated Signal Control

Aerial photograph of road

Abstract

Queueing delay at a traffic signal can be generally estimated as the sum of two components, uniform delay and overflow delay. The delay formula in the 1985 Highway Capacity Manual (HCM) applies primarily to lane groups under pretimed control. Although the HCM contains a method for estimating cycle length and splits under vehicle-actuated operation, the resulting effect on delays has yet to be verified. Furthermore, the HCM assumption of "snappy" operation and its inability to compare pretimed and actuated control have been criticized in the literature. An approach for estimating overflow delays for lane groups under vehicle-actuated control using the current HCM delay model format is presented. An existing cycle-by-cycle simulation model has been modified to produce delay for a basic vehicle-actuated signal operation. Overflow delay is computed as the difference from total simulated delay minus estimated uniform delay for the average cycle conditions. The results indicate that the average cycle and overflow delays are very much related to the controller settings such as minimum and maximum greens and cycles and unit extensions, with longer unit extensions producing higher cycle length and overflow delay. Furthermore, applying the 1985 HCM formula to the simulated signal settings resulted in much higher delays, which implies the need for separate calibration of the second delay term to account for the actuated control effects. The simulation model was executed to produce a calibration data base for an analytical overflow delay model.

Reference

LI, J., ROUPHAIL, N.M. and AKÇELIK, R. (1994). Overflow Delay Estimation for a Simple Intersection with Fully Actuated Signal Control. Transportation Research Record: Journal of the Transportation Research Board. No. 1457 (Part 2). pp 73-81.