Traffic Calming

This skewed intersection was modified to slow vehicle speeds and increase awareness at the intersection.

Traffic calming is a way to design streets, using physical measures, to encourage people to drive more slowly. It creates physical and visual cues that induce drivers to travel at slower speeds. Traffic calming is self-enforcing. The design of the roadway results in the desired effect, without relying on compliance with traffic control devices such as signals and signs, or on enforcement. While elements such as landscaping and lighting do not force a change in driver behavior, they can provide the visual cues that encourage people to drive more slowly.

The reason traffic calming is such a powerful and compelling tool is that it has proven to be so effective. Some of the effects of traffic calming, such as fewer and less severe crashes, are clearly measurable. Others, such as supporting community livability, are less tangible, but equally important.

Experience throughout North America, Europe and Australia, and has shown that traffic calming, if done correctly, reduces traffic speeds, the number and severity of crashes, and noise levels. Research on traffic-calming projects in the United States supports their effectiveness at decreasing automobile speeds, reducing the number and severity of crashes, and reducing noise levels for specific contexts. Looking at a sample of various speed studies shows that typical speed reductions of 5 to 20 percent at the 85th percentile speed can be realized by the use of traffic-calming measures—including mini-circles, chicanes, speed tables and other standard traffic-calming devices. Use of several of the traffic-calming measures have also resulted in substantial reductions in motor vehicle crashes. For example, the implementation of traffic mini-circles at over 700 locations in Seattle has resulted in a reduction of approximately 90 percent of intersection accidents.