Simulation results of deploying TSP along the Columbia Pike corridor in northern Virginia.
Arlington, Virginia, United States
Evaluation of Potential Transit Signal Priority Benefits Along a Fixed-Time Signalized Arterial
Summary Information
This study used the INTEGRATION simulation model to estimate the impact of implementing transit signal priority (TSP) on a 3.95 mile section of Columbia Pike in Arlington, Virginia. Baseline corridor and cross street traffic flows were determined from field data collected between June 12 and 14, 2000. Saturated traffic flow parameters were estimated based on corridor geometry.
The model was designed to reflect the geometric location and configuration of multiple bus stops and intersections on the corridor. The transit signal priority scheme gave priority to buses traveling on Columbia Pike or entering the corridor from major cross streets. The signal priority logic enhanced the existing optimized fixed-time signal control system by enabling transit vehicles to receive a five second green extension if approaching an intersection at the end of a green cycle. The model considered vehicle movements only, and did not account for pedestrian clearance intervals or the impact of emergency vehicle signal preemption. In addition, if two transit vehicles called for priority simultaneous at the same intersection, no priority was given.
The simulation model was run to determine the impacts of TSP on AM peak and midday traffic flows. Two time periods were examined: 7-9AM (AM Peak, heavily directional travel towards Washington, D.C.) and 11AM-1PM (Mid-day, off peak, balanced travel). The two periods were divided into 15 minute intervals for the model runs. Four scenarios were examined for the AM Peak period:
- Base case - no priority
- TSP for express buses only
- TSP for express and other buses traveling along the Columbia Pike
- TSP for all buses at the intersections in the corridor, regardless of direction.
Peak period person delays were calculated based on the assumption that passenger cars carried 1.2 persons per vehicle, and transit vehicles carried 23 persons per vehicle. During non-peak hours, transit vehicle were assumed to carry 16 persons per vehicle.
Findings
For the AM peak, the initial simulation results indicated that the provision of transit priority at all intersections between Dinwiddie and Queen was generally beneficial to buses.
- For the Columbia Pike express buses, statistically significant reductions in travel time (-2.3 to -2.5 percent), delays (-3.7 to -4.1 percent), vehicle stops (-1.3 to -2.7 percent), and fuel consumption (-1.1 to -2.7 percent) were obtained when priority was provided exclusively to them or in conjunction with other buses running along the arterial.
- Regular Columbia Pike buses also experienced statistically significant reductions in travel time (-4.8 percent), delay (-7.6 percent), stops (-1.8 percent), and fuel consumption (-1.9 percent) when priority was granted to them.
- In this case, maximum increases in travel time, delays, stop and fuel consumption incurred by the general traffic were reduced from 19.3 to 5.7 percent, 26.4 to 8.7 percent, and 4.7 to 1.8 percent, and 4.8 to 2.4 percent, respectively.