At an intersection in Eindhoven, the Netherlands a transit signal priority system reduced bus schedule deviation by 17 seconds.
The study described in this paper measured the impact of conditional signal priority on schedule deviation by measuring the difference in the deviation of individual vehicles from their schedule as they passed through a signalized intersection. Conditional signal priority refers to a system that only provides transit vehicles with extended green time of an extra green phase when the in-vehicle computer indicates that the bus is behind schedule. Field measurements at one intersection along a route in Eindhoven found that the average absolute value of schedule deviation decreased by 17 seconds on the day when conditional priority was active, and increased by an average of 11 seconds on the day without conditional priority. This indicates that conditional priority was effective in bringing the vehicles closer to their scheduled running time at this particular interseciton.
In addition, the study investigated the impact of several operational control strategies on schedule reliability. A simulation of a simplified transit route was used to assess the impact of four strategies on the performance of vehicles:
- No control – operating without intervention based on the deviation of the vehicle from schedule.
- With holding – holding vehicles at each stop, if early, to wait for scheduled departure time.
- With conditional priority – buses given signal priority when they are running behind schedule.
- With holding and conditional priority.
The simulated route consisted of four stops separated by route segments with an average running time of 10 minutes each with a standard deviation of 2 minutes. Scheduled running time was assumed equal to the average running time. The performance measure used to assess the impact of each control strategy was the central schedule deviation band, which the authors define as the band between the 15th percentile and 85th percentile of schedule deviation. Without control strategies, the simulation found this band to be [-3.5, 3.5], indicating that 15 percent of the transit vehicles arrived more than 3.5 minutes ahead of schedule and 15 percent arrived more than 3.5 minutes late. Holding early buses at stops until their scheduled departure time improved this range to [0, 4.1]. Conditional priority without holding further improved performance to a range of [-1.9, 1.9]. The best operational strategy, incorporating both holding and conditional priority, reduced the range to [0, 2.0]. When compared to conditional priority alone, this strategy reduces early arrivals while only increasing the late end of the range by 0.1 minutes.
Field measurements confirmed the positive impact of conditional signal priority. The central deviation band at the intersection described previously improved from [-3.3, 2.5] without priority to [-1.0. 2.2] when priority was operational.
See related benefits database entry:
Furth, Peter G. and Theo H.J. Muller. "Conditional Bus Priority at Signalized Intersections: Better Service Quality with Less Traffic Disruption," Paper presented at the 79th Annual Meeting of the Transportation Research Board. Washington, DC. 9-13 January 2000.
Integrating Bus Service Planning with Analysis, Operational Control, and Performance Monitoring
Author: Furth, Peter G. and Theo H. J. Muller
Published By: Paper presented at the 10th Annual ITS America Meeting. Boston, Massachusetts
Source Date: 1-4 May 2000
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bus priority, traffic signals, TSP, paratransit, demand-responsive transit