May/June 2000, p.12-13

Shrinking Roads Shrink Traffic

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A landmark 1994 British government study by the Standing Advisory Committee on Trunk Roads and Arterials (SACTRA) conclusively showed that building more roads or widening existing ones generates more traffic. This concept that traffic is elastic-that it can fluctuate based on changes in road capacity-is an analytical cornerstone of the auto-reduction movement. But while the SACTRA study proved that expanding existing roads induces more traffic, until recently there had not been a study that investigated the logical flip side of the equation: whether closing or narrowing roads-reducing road capacity-results in reduced, or 'disappearing' traffic.

The new study, Traffic Impact of Highway Capacity Reductions: Assessment of the Evidence, sponsored by London Transport and the Department of Environment, Transport, and Regions, tackles the issue of reduced capacity or 'disappearing' traffic. Based on over 100 individual case studies, it examines the short- and long-term impacts on traffic of both large and small-scale incidents of loss or reallocation of road capacity. The study concludes that the average overall reduction in traffic after such a change was 25%, and that "to find so many cases of reductions in traffic, at a time when increasing car ownership and general traffic growth create prevailing expectations of increases shows a balance of evidence that a proportion of traffic can indeed 'disappear' when capacity is reduced."

A car-free Washington Square today.Look at the examples right here in our own backyard. When 5th Avenue was closed to cars at Washington Square Park in 1958, newspapers and traffic planners alike predicted a traffic nightmare, but the traffic failed to materialize. In 1973, when the West Side Highway was closed after a collapse, forecasters once again foretold chaos on the West Side. Yet, not only did the promised snarls fail to materialize, but the traffic on the West Side actually decreased by 8% over the following two years.

More dramatic examples can be found in Europe, where cities have pedestrianized and traffic calmed whole areas. When Freiburg, a city of approximately 200,000 in Germany, closed most of its city center to vehicle traffic, the result was a 12% decline in traffic on the roads surrounding the city center over 10 years, despite a significant increase of car ownership in the town. The decline in drivers was offset by an increase in public transportation use, walking and biking. In 1976, 22% of trips into the Freiburg area were by public transportation, 18% biking or walking, and 60% by motor vehicle. In 1995, 26% of trips into the city were by public transportation, 28% biking or walking, and only 46% were by motor vehicle. Similarly, when Nurnberg, a city of 480,000 in northern Germany renowned for its progressive transportation policies, pedestrianized the majority of its city center in the late 1980's, traffic not only decreased remarkably in the city center, but also decreased by approximately 5% city-wide.

Washington Square Arch was bisected by 5th Avenue until 1958.The British study proves that 'disappearing' traffic is a fundamental part of transportation system dynamics and also questions long-held assumptions regarding transportation planning. The extensive evidence in this study shows that the only sure-fire way of reducing congestion is to reduce road capacity and re-allocate road space to more sustainable modes of transportation rather than build new roads and widen existing ones.

The study also validates T.A.'s long-standing claim that reducing road capacity via projects like the Downtown Brooklyn Traffic Calming Project, and closing Central Park and Prospect Park to cars will result in less overall traffic in the surrounding areas. NYC traffic planners and engineers should take note: traffic does in fact disappear when roads are closed, narrowed or torn down.

Source: "Traffic Impact of Highway Capacity Reductions: Assessment of the Evidence" (MVA, March 1998, Landor Publishing).

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