vehicle emissions per mile traveled increase due to more aggressive acceleration, braking, and use of second gear, traffic calming will likely lead to overall emission reductions due to its influence on travel demand (see Table E-1).

A recent FHWA report discusses the German experience with traffic calming in six cities and towns in the early 1980s:

The initial reports showed that with a reduction of speed from 37 km/h (23 mph) to 20 km/h (12 mph), traffic volume remained constant, but . . . air pollution decreased between 10 percent and 50 percent. The German Auto Club, skeptical of the official results, did their own research which showed broad acceptance after initial opposition by the motorists. Interviews of residents and motorists in the traffic calmed areas showed that the percentage of motorists who considered a 30 km/h (18 mph) speed limit acceptable grew from 27 percent before implementation to 67 percent after implementation, while the percentage of receptive residents grew from 30 percent to 75 percent. (Project for Public Spaces 1992)

This experience of initial skepticism of traffic calming, followed by its widespread popularity after implementation, has been experienced in hundreds of communities across Europe, Japan, and Australia, along with the few U.S. communities that have adopted such strategies, such as Palo Alto, California, and Seattle, Washington.

Reducing Road Capacity with Traffic Cells for Environmental Benefit

Many places in Europe and Japan—cities such as Göteborg, Sweden, Hannover, Germany, and Osaka, Japan; suburban new towns such as Houten, Netherlands; and established automobile-oriented suburban centers such as Davis, California—have successfully implemented traffic cell systems. These typically consist of a set of radial pedestrian, bicycle, and transit-only streets focused on a central area. Whereas pedestrians, bicyclists, and public transportation can freely cross these streets, automobile traffic cannot, but must instead use a ring road around the center. Traffic cell systems are very effective at



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