Impacts of Coordinated Traffic Signal Control Strategies and Bus Priority.

Swedish urban traffic signal systems are normally coordinated with fixed time plan selection. Within this framework local traffic actuated signal timing adjustments are applied based on detector inputs aimed to reduce the number of vehicles in the dilemma zone. Active bus priority is also achieved with the aim to display green signal at the arrival of the bus to the stop line. Due to lack of knowledge of traffic performance impacts of these techniques a major research study was undertaken funded by the Swedish Road Administration. The aim was to evaluate the following control strategies using Stockholm as case study: 1) Fixed time coordination (FTC); 2) Fixed time coordination with local signal timing adjustment (FTC-LTA); 3) Same as 2) + active bus priority (PRIBUSS); 4) Self-optimizing control (SPOT). The methodologies for the study included field data collection using mobile and stationary techniques, offline signal timing calculations with TRANSYT; microscopic simulation modeling using the HUTSIM model. The study obtained the following results: (1) Local traffic adjustment with the manual FTC reduced total delay with 1%. (2) Signal timings determined using TRANSYT reduced the average intersection delay with 9% compared to manual signal settings. (3) Local traffic adjustment reduced total delay with a further 5%. (4) Bus travel time was reduced by 11% using PRIBUSS, and 28% using SPOT. (5) Travel time for all vehicles did not increase using PRIBUSS, and was reduced by 6.5% with SPOT. Results of comparing PRIBUSS and SPOT to FTC-LTA were shown to be statistically significant.