NETSIM-Based Approach to Evaluation of Bus Preemption Strategies

Abstract

Preemption techniques are designed to provide preferential treatment to buses at signalized intersections. Uncertainties resulting from variations in passenger boardings and unboardings at bus stops make the prediction of the exact arrival times of buses at intersections extremely difficult. A preemption strategy, if properly designed, can provide continuous green phases to buses at successive intersections. It is unfortunate that a validated technique that can be used to assess the possible consequences of signal preemption is not available. The authors present the application of a simulation model, NETSIM, to make such an assessment. NETSIM was selected because of its ability to microscopically simulate vehicular movements on a street network and its ability to track an individual vehicle from the source to the sink by the use of an animation feature. A major bus route in Ann Arbor, Michigan, was used as the experimental site. The major conclusions are that NETSIM, when properly validated, can generate delay and queue-related measures of effectiveness that are compatible with field data and that the animation feature of NETSIM can be used to assess the operational consequences of bus preemption on a series of intersections on a bus route. For the volume levels studied in the project, savings in delay along the bus route resulting from preemption exceed the increases in delay along the cross street. Further research is needed to determine whether the net savings in delay, when balanced against the costs of installing and maintaining the system and the inconvenience to motorists along the cross street, make the system worthwhile.