Evaluating the Benefits and Costs of Road Pricing in Seattle / ロードプライシングの社会的便益の検証

日本語解説は後述されております/Japanese message follows

Since the onset of motorization, most American cities have suffered from constant traffic jam and air pollution. Traditionally, policy makers have attempted to solve this problem through supply-side solutions, meaning building more roads and expanding freeways. They however haven't been effective in easing congestion, and in recent years, this encouraged some policy makers to take a look at the demand-side of the problem. London examined various transportation demand management (TDM) strategies and decided to implement congestion charging (road pricing) to keep cars from entering central London, using an electronic tolling system (see picture below). The result was dramatic; according to Transport for London, an agency responsible for transportation system in London, the traffic volume in the city center declined by 16% between 2002 and 2006.

Electronic Tolling System in Stockholm (photo credit: ITS International)

Seattle, where I spent many years of my academic career, has been contemplating some sort of road pricing, especially after Mayor McGinn took the office in 2008, and I thought it would be interesting to estimate the overall impact of London-style road pricing scheme in Seattle. I conducted the study with my fellow students at the University of Washington, and the paper is now published on the school's journal.

The paper basically forecasts the impact on traffic volume first, and estimate the secondary impacts such as reduction in travel time and air emissions. My analysis using an elasticity-based approach shows that the traffic volume bound to/from downtown Seattle can be reduced significantly; the following table shows the impact of road pricing at $3.00 per entry to the designated cordon in downtown Seattle.

Change (%)
Number of Vehicles
Entering the City Center
GHG Emissions
CO Emissions
NO Emissions
VOC Emissions
Particulate Matter
Traffic Accident
Travel Time

These impacts are monetized using a standard benefit-cost analysis method, and after considering capital, operation, and direct and indirect financial costs of the program, the estimated net benefits would be $585 million.

Even with such positive analysis result, many residents would react negatively to the idea of using toll to make them use other modes of transportation. Nonetheless, Seattle has just established a toll on a bridge connecting to the neighboring city of Bellevue to pay for its replacement and maintenance costs, and more roads are expected to be tolled to pay for the infrastructure costs. These should gradually get residents used to the idea of paying for road, and they would realize the non-monetary benefits of road pricing in the long run. With this in mind, I hope the analysis result of this study will guide Seattle and other cities to tackle traffic congestion and air pollution effectively in the future.

Steven Danna, Keibun Mori, Jake Vela, Michelle Ward, 2012. "A Benefit-Cost Analysis of Road Pricing in Downtown Seattle," Evans School Review, Vol. 2, No. 1.








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