In 2006, the U.S. DOT initiated the UPA (Urban Partnership Agreement) program to demonstrate congestion reduction through strategies consisting of combinations of the 4Ts: Tolling, Transit, Telecommuting/TDM, and Technology. The Seattle/LWC UPA projects focused on reducing traffic congestion on SR 520 between I-405 and I-5, a heavily-traveled, east-west commuter route across Lake Washington. The lake separates Seattle from the eastern suburbs (including Bellevue and Redmond). These strategies included tolling all lanes of the SR 520 bridge, adding bus service in the SR 520 corridor, implementing active traffic management systems, and real-time traveler information signs on highways and at transit stops and stations. The suite of projects had a combined benefit-to-cost ratio of 1.76 due to travel time savings and reduced emissions.
Statistical comparison of changes in mean travel times within each peak period was conducted using a linear mixed-effect modeling technique. Factors known to potentially influence the traffic patterns are accounted for in the models, while fixed-effect results indicate the magnitude and statistical significance of UPA deployment impacts.
After deployment of electronic tolling on SR 520, meaning morning peak period travel time decreased by 2 minutes in each direction, a 25 percent reduction in mean travel times across Lake Washington. Mean afternoon peak period travel time decreased by 2 minutes eastbound and 8 minutes westbound. Concurrently, travel times increased on surrounding and alternative routes, including I-5, I-90, and SR 522, by up to 3 minutes.
Monetized through the application of financial modeling, the travel time savings of the Seattle/Lake Washington Urban Partnership Agreement totalled $250,573,714.