Traffic Calming

Traffic Calming

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Overview

Traffic Calming is the deliberate slowing of vehicle speeds on a public or private street by means of vertical or horizontal deflection devices or through roadway geometries. Where high speed traffic discourages pedestrians, traffic calming can achieve a better balance between vehicles and pedestrians livable streets , a goal championed by Donald Appleyard in the 1970's.

The traffic calming effectiveness of a deflection device increases as the required deflection is increased. Typical devices employed in the U.S. are speed humps, curb extensions (pictured), and medians . More advanced traffic calming measures include bollards , the chicane , traffic circles, raised intersections , a raised crosswalk , and road diets . Visual features such as tall trees and buildings close to the street edge, and roadway striping that creates narrow travel lanes, have also been found to reduce traffic speeds.

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History

Slow Acceptance

Traffic calming has been integral to street design in European countries for decades. Its acceptance in the U.S. has been far slower. Since the 1970's, some cities have employed aggressive speed bumps and stop signs, generally on residential streets. This approach introduced new problems: drivers learned to ignore stop signs where cross-traffic was infrequent, and tall speed bumps resulted in complaints of noise from nearby residents, discomfort for drivers, and vehicle damage from fire departments and trash collection services. In some cases, residents began opposing the use of traffic calming because of these poor practices. During the 1980's and 90's, more sophisticated traffic calming approaches were developed, focussing less on vertical deflection such as speed bumps, in favor of horizontal deflection devices such as traffic circles, raised medians, and curb extensions.

Traffic Calming Leaders

Today, traffic calming is used widely in much of the U.S. but particularly among a few noteworthy leaders, including Austin, Texas; Bellevue, Washington; Eugene, Oregon; Charlotte, North Carolina; and Sacramento, California.[1] These cities have gone beyond employing traffic calming to slow traffic. They have used more aggressive devices such as raised crosswalks and raised intersections to give pedestrians and bicyclists greater priority, to the point of placing them on equal footing with cars and trucks.

Effectiveness

Slower Traffic, Fewer Crashes

A number of studies of traffic calming installations show they are effective in both reducing average traffic speed and eliminating the highest speeds.

Reducing Liability

A frequently offered objection to traffic calming proposals -- usually by traffic engineers -- is the perception of increased risk of liability, due to drivers colliding with unexpected traffic calming devices. Collision records indicate just the opposite. A comprehensive report from the Institute of Transportation Engineers [3] notes, "[a] survey of 98 traffic agencies uncovered only 6 lawsuits related to traffic calming, this among agencies that collectively reported over 1,500 traffic-related lawsuits each year. These same agencies reported paying only two damage claims [4]. A survey of 407 urban traffic agencies found legal liability to be their greatest concern about use of speed humps. Yet, among the dozens of agencies using speed humps at that time, only one had ever paid a damage claim, and this for only $2,500." [5] The overwhelming evidence thus indicates jurisdictions are far more vulnerable to litigation when they fail to address chronic speeding problems through widely accepted traffic calming techniques.

ALSO ON THE LIVABLE STREETS NETWORK

Streetfilms: The Diverter

Streetfilms: Traffic Calming Done Right in Melbourne

REFERENCES

[1] Ewing, Reid, Hofstra, Amy, and Lane, Robert. "Traffic Calming Initiatives - Approaching the Tipping Point." Planning Magazine, February 2007. http://www.activelivingresearch.org/files/Ewing_Planning%20Magazine.pdf.

[2] Ewing, Reid. Traffic Calming: State of the Practice. Washington, DC, USA: Institute of Transportation Engineers/Federal Highway Administration, 1999.

[3] Ibid., Chapter VI. Legal Authority and Liability.

[4] R.S. McCourt, “Survey of Neighborhood Traffic Management Performance and Results,” in Harmonizing Transportation & Community Goals (ITE International Conference, Monterey, CA, 1998), Institute of Transportation Engineers, Washington, DC, 1998.

[5] ITE Technical Council Committee 5B-15, “Road Bumps— Appropriate for Use on Public Streets,” ITE Journal, Vol. 56, November 1986, pp. 18–21.