Bhargava Rama Chilukuri

Among the different strategies adopted to improve the efficiency and reliability of the bus services, bus signal priority is a low cost and less infrastructure- demanding solution that has the potential to reduce bus travel times in urban arterials. This paper develops analytical models for finding the thresholds for Green Extension (GE) and Red Truncation (RT) for a four-phase signal system with buses on conflicting phases. The thresholds are developed based on reducing the total person delay after considering buses from the current cycle and unserved buses from the previous cycle for priority decisions. The proposed models aim for zero-delay service for the buses from the current cycle and reducing delay for the unserved buses from the previous cycle. The models reveal that at multi-phase signals, several bus priority alternatives are possible to reduce total person delay and agencies can choose alternatives based on their requirements and constraints. These models are evaluated in VISSIM microscopic simulation environment. The evaluation results indicate a 16.7 to 42.8% reduction in total person intersection delay due to the implemented bus priority.

This study evaluates and compares two major solutions used to mitigate the problem of delay of public transport buses at signalized intersections in urban arterials. The solutions considered are to implement bus signal priority (BSP) at intersections and to provide dedicated bus lanes (DBL). Comparison of performance is done in terms of travel time. Study site selected is a 5 km stretch in the IT corridor in Chennai for the DBL and with four intersections in that corridor for the BSP. Only the southbound movement is considered for the analysis. To evaluate the selected strategies, the study site was simulated in VISSIM, which is a micro-simulation software. Road, traffic, and control details from field were used as input, and a calibrated network was created. Using that, four scenarios were studied: 1. base condition with fixed time signals and no dedicated lane, 2. fixed time signal with DBL, 3. BSP without dedicated lane, and 4. BSP and DBL. Conditional Green Extension and Red Truncation priority strategies using Visual Vehicle Actuated Programming (VisVAP) from VISSIM were used for the BSP implementation. For dedicated bus lane condition, the mode preference was altered for the southbound movement links and the bus movement was allowed only in the left-most lane, which was kept as DBL. Results showed the bus signal priority having maximum impact in terms of reduction in total travel time. In the case of dedicated bus lane condition, travel time reduced effectively for bus mode, but with an increase in travel time of other modes.