An Evaluation of Alternative Permissive Periods on Non-Coordinated Phase Performance in Coordinated Traffic Signal Systems

Currently, there are some concerns regarding coordinated-actuated traffic signal operations. First of all, there is no consistent nomenclature to describe coordination modes. Different traffic signal controller manufacturers use different terminologies and their terms are not necessarily meaningful or intuitive. Actually, one can find inconsistency in the terminology used even by a specific manufacturer just by trying to understand (or decipher) the manual. Secondly, and this might be just a consequence of the first concern, it seems that many traffic engineers and technicians are not aware of the particularities and differences among the coordination modes.

The main purpose of this study was to investigate the main issues related to non-coordinated movements of coordinated-actuated traffic signals. A set of terms and definitions including permissive point and permissive period was proposed. Based on this terminology, three coordination modes were presented and their performances were evaluated for three different volume/capacity (v/c) ratios by using hardware-in-the-loop (HITL) simulation.

Using average vehicle delay as the measure of effectiveness (MOE), statistical analyses indicated that for moderate v/c ratios (0.50), the three coordination modes did not perform differently. For lower v/c ratios, differences among the modes were observed.

The results of this thesis research provides some guidance on the use of coordinated-actuated traffic signal operation by letting traffic engineers and professionals be aware of the various effects that different coordination modes might cause on the intersection performance.