Traffic Calming: An Overview

by Walter Kulash,

Glatting Jackson Kercher Anglin Lopez Rinehart, Inc.

Progress – July 1996


Traffic Calming: A Rapidly Growing Practice

Traffic calming devices are simple street design features that cause motorists to drive with more care, to drive more slowly or perhaps via another route.

The great majority of traffic calming devices make slight alterations to the street’s geometry, reducing its real or perceived width, or causing the driver to negotiate curvature or pavement texture. These modifications, almost always made within the public right-of-way, are usually accompanied by extensive landscaping, and serve as neighborhood landmarks as well as traffic calming devices.

Borrowing heavily from European and Australian experience, US cities have installed hundreds, possibly thousands of traffic calming devices over the past decade. Originally seen as devices to “retrofit” existing streets, traffic calming is now also seen as a part of original street design in new communities.


Why Calm Traffic?

Traffic calming measures are proposed in response to these widely-experienced problems:

Cut-Through Traffic-Cut through traffic has neither its origin nor its destination within the neighborhood, but rather is passing through the neighborhood on its local streets. Traffic engineers intend that through traffic use the major arterial streets, not neighborhood streets. This does not always happen, and cut-through trips seek out the local streets, sometimes because they are faster, and often because they are more pleasant and therefore seem to be faster.

Speeding-Many motorists (neighborhood residents as well as “cut throughs”) drive too fast on local streets. While some speeding is by irresponsible drivers, the majority is done by normally responsible drivers who find themselves “invited” to speed by the road’s design features, such as excessively wide pavement, straight sections of road and absence of vegetation. In addition to safety issues, speeding vehicles degrade the quality of the street for all other users, signaling that the street is extremely devoted

to traffic, imparting a general feeling that things are “not right” in the neighborhood.

Security – Excessive traffic speeds are a threat to neighborhood security, causing residents to retreat into their homes, essentially abandoning the street to vehicles and whoever else wants to claim it. Reducing traffic speeds and volumes through traffic calming measures are powerful ways for residents to start to reclaim their streets for their own needs.

Aesthetics-Wide expanses of pavement devoted solely to the moving of traffic have taken over much of our communities in the name of “traffic service.” Traffic calming provides the opportunity to use streets not only for moving cars but also as an aesthetically pleasing focal point for the community.


Menu of Traffic Calming Devices

Although there is a seemingly endless variety of traffic calming devices, they all derive from some combination of a few basic principles:

Narrowing the street reduces the speed that most drivers find reasonable and comfortable (the “design” speed). Narrowing is done through reducing the pavement width, adding parking to the street, or adding a median. At intersections, narrowing is complemented by tight corner radii. The perception of narrowing, which can be as effective as actual narrowing, is gained with street trees along the curb, overhead tree canopy, buildings brought close to the street and “gateways” along the street.

Deflecting the vehicle path causes the driver to slow and devote more attention to the task of driving. Deflection usually terminates long, straight (“tangent”) street views, thereby reducing their design speed. Deflection is done through curving the travel path of the automobile.

Sharing the pavement with other vehicles is a powerful way to slow traffic and raise the attention level of drivers. Long a feature of traditional local streets, shared-use can be re-introduced into other streets by selective short sections of narrow pavements, either at mid-block locations or near intersections. On-street parking can also compel shared use of the street.

Diverting the driver’s route makes vehicular access more difficult, and encourages the driver to use another route.

Diagonal street closures, one-way streets, median closings and turning movement restrictions are primary examples of diversion. Closing the entire street is EMPHATICALLY NOT an acceptable traffic calming solution.

Changing the pavement surface demands attention from drivers, and reduces the comfortable driving speed (the “design” speed).

Standard traffic control devices slow traffic through regulation. STOP signs, four-way STOP signs, turn-movement prohibitions, traffic signals and posted speed limits are the devices most frequently used to calm traffic.

Intensified enforcement of traffic regulations can calm traffic, generally by reminding drivers of posted speed limits and by enforcing the observance of STOP signs. Police officers are the usual source of intensified enforcement, but neighborhood volunteers can also provide effective work in this area.


Striking A New Balance

Traffic calming measures, while simple in concept, are a complete change in direction from conventional traffic planning of the past three decades. In conventional traffic planning, moving the most possible traffic at the highest affordable speed is the highest priority, and almost no neighborhood values are allowed to interfere. Traffic calming gives a new balance between traffic service and important neighborhood values, such as safety, walking and bicycling.



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Filed under New Urbanism: Timeless, Traditional, Walkable Design

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