Modeling bus priority with intermittent bus lane for local traffic conditions

Abstract

Transit priority strategies have been implemented in many cities to improve levels of service for transit passengers and to encourage modal change. So far, researches on these methods encompass homogeneous traffic flow operating in disciplined lane movement, which is not the case in Dhaka city, where mixed traffic dominates and lacks lane discipline resulting traffic mishaps. Hence, this study endeavors to develop new-fangled bus priority schemes and evaluate its effectiveness in improving the road network performances by making quantitative comparison with existing priority methods to identify the most viable scheme for local traffic conditions. A wide range of traffic data of two peak periods comprising 7 hours of traffic flow in each of the 3 consecutive days, had been recorded and later extracted using image processing technique, from a section of 6-lane major artery road–Kazi Nazrul Islam Avenue to model the road network initially, which was later calibrated to simulate mixed traffic system. Furthermore, for each considered priority schemes, 20 different scenarios with varying traffic volume and bus to vehicle ratio have been simulated with VISSIM for 16,92,000 simulation seconds in total, to evaluate the effectiveness of priority methods for prevailing traffic conditions in terms of average traffic delay. The study proposed bus priority with intermittent bus lane, a new concept for dynamic bus lane, as to prioritize bus without compromising delay of other traffic, and hence, developed algorithm for simulating it in an urban road network for local traffic conditions, using Vehicle Actuated Programming within microsimulation software VISSIM. This priority method makes a lane intermittently dedicated to bus rather than exclusively dedicating the lane, making the prioritization of public transport adaptive with its demand in a signalized corridor. Furthermore, when the lane is not dedicated to bus, active bus priority was incorporated to improve the mobility of public transport upon the detection of bus prior to signal. Results show that bus signal priority minimizes average delay per vehicle by at least 40% or in some cases up to 120% more than what dedicated bus lane does in an urban road network having mixed traffic conditions, whereas the case is totally opposite while considering minimization of average delay per bus only due to the fact that even though signal priority is triggered upon the detection of bus prior to the signal, other vehicles get the advantage of green extension in case of active priority due to weak lane discipline that increases the degree of uncertainty of reaching the bus to stop line before red phase starts. This study also perceives proposed priority scheme to be effective in low volume of traffic with bus demand, referred as bus to vehicle ratio, up to 17.5% in the road network. Further rise in the bus demand makes dedicated bus lane preferable for the prevailing traffic condition. However, in case of bus demand below 12.5%, the priority method seems more potent in ameliorating the network performances up to 3500 veh/hr at most than other priority rules. This research may be used as a good reference for policy makers to choose the best bus priority alternatives by assessing their suitability for the prevailing traffic conditions of the road network under consideration.