This study examined the improvement in journey time and speed of transit vehicles using transit signal priority (TSP) in Portland, Oregon. GPS, and an existing automatic vehicle location (AVL) and computer aided dispatch (CAD) system were used to monitor system performance. TSP was granted only if a bus was behind schedule. An on-board transit vehicle trip monitoring system determined if a bus was late by comparing the scheduled time for passing a specific location to the actual time the bus passed this location. The data collected were used to conduct a corridor level and intersection level analyses.
Corridor Level Analysis
Performance and location data were collected during weekday peak and non-peak hours during two separate four week periods to evaluate the impacts of TSP on corridor level journey time on Route-12 which handles traffic southwest of Portland traveling to and from the central business district.
TSP was "on" from 9/24/01-10/18/01, and TSP was "off" from 10/22/01-11/15/01. The results showed that when TSP was "off"
- Median inbound journey times increased 0.4 percent during the AM peak,
- Median inbound journey times increased 2.3 percent during the PM peak, and
- Median inbound journey times increased 0.5 percent during the non-peak.
- Median outbound journey times increased 3.1 percent during the AM peak,
- Median outbound journey times increased 4.2 percent during the PM peak, and
- Median outbound journey times increased 1.5 percent during the non-peak.
Intersection Level Analysis
At the intersection of SE 82nd Avenue & SE Division Street, transit vehicle speed was measured during peak periods before and after TSP implementation. Run times were calculated by subtracting the departure times at the bus stops upstream of the intersection from the arrival times at the downstream stops. Bus speeds were determined from the mean run times (in each direction of travel) and the combined distance between stops.
The "before TSP" data was collected in April 2001, and the "after TSP" data was collected in April 2002. After TSP was implemented on the SE Division Street corridor
- Speed increased approximately 7.7 percent during the AM peak,
- Speed increased approximately 13.7 percent during the PM peak, and
- Speed increased approximately 2.9 percent during the all-day period.
In this study, Tri-met intended to minimize impacts on opposing traffic by granting signal priority benefits only to buses running excessively behind schedule. The collateral impacts on other traffic; however, were not evaluated in this report.