Evaluation of traffic signal control system using a system-wide performance measure under two-fluid model theory

This study compared the performance of an adaptive traffic control system and a semi-actuated coordinated control system using trip time and stop time relation under the two-fluid model theory. Using the test vehicle data collected for the evaluation of SCATS in Cobb County, Georgia, the parameters were estimated and interpreted. At the initial interpretation, potentially conflicting recommendations could be drawn from the individual route-period group level comparisons and the two-fluid model results. Therefore, a new interpretation combining the two approaches was presented. The new approach resulted in curves representing restricted ranges of the trip time versus stop time relationship. Using the curves and a two-fluid model assumption, the fraction of moving vehicles in the network can be obtained. Unlike the measures adopted in the previous traffic signal system evaluation studies, such as mean travel time and speed, this measure is defined by all time periods and routes data, allowing for a system-wide performance measure. Application of this measure showed that under SCATS approximately 10% more vehicles were moving on end-to-end type routes when the network was most congested and 15% to 20% less vehicles were moving on side-street to side-street type routes over different traffic concentration levels.