Comparative Safety Evaluation of SCATS and Pre-Timed Control System

Bodke, Sujay, Brian Dara, and Utpal Dutta

Since 1992, traffic signals in Oakland County and a portion of Macomb and Wayne counties of Michigan have been converted to the Sydney Coordinated Adaptive Traffic System (SCATS). County traffic engineers have been adjusting various SCATS parameters to improve its effectiveness in terms of delay, traffic flow, queue length, and crash and injury occurrences.

In 2008, a study was conducted to evaluate the performance of the SCATS system on M-59, between Pontiac lake East to Pontiac Lake West in Waterford Township, Michigan, in terms of delay, flow, queue length and fuel consumption and emissions. As a part of this study various performance parameters of the SCATS systems was found to be compared with Pre-Timed signal system. Performance of the SCATS system was found to be superior for several of the performance measures during each peak period. When compared to pre-timed signal, installations and maintenance cost of SCATS system is almost two times greater. Therefore, there is a need to determine the added related benefits of SCATS system. In this context, determination of cash benefit of SCATS can play a significant role. If we combine congestion and crash related benefits, then it is most likely that combined benefits will overweight the cost.

Crash data from 1999 to 2008 of two corridors, one controlled by the SCATS and other by the Pre-Timed signal system were examined to determine the effectiveness of SCATS system. In order to evaluate the effectiveness of SCATS signal system, intersections as well as segment crash data before and after the installation of SCATS signal were compared. In addition, a series of statistical tests were performed to compare safety performance of SCATS and pre-timed signal systems. It was observed that there was shift in severity types A and B to C, which noteworthy. Finally, cost related information for both SCATS as well as pre-timed was also computed and compared.