Traffic Calming

In all facets of transportation planning, the automobile asserts its dominance. From highways to arterial and collector streets and down to local roads, infrastructure design has placed the automobile at the apex of the transportation hierarchy. Well-paved roads with wide lanes, along with incomplete or nonexistent sidewalks, crosswalks, and bicycle lanes, have resulted in a sprawling built environment.

Yet, until the 20th century, the design of communities was oriented primarily around the pedestrian. Characterized by mixed land use, a grid of connected streets, and moderately high densities, traditional land use patterns were noted for their connectivity and accessibility. As a result, these types of communities are deemed “walkable” in today's parlance.

Following World War II and beginning with the widespread construction of the suburbs and the interstate highway system in the 1950s, this walkable neighborhood design was increasingly replaced by dependence on the automobile. Cul-de-sacs were substituted for connector roads, blocks became larger, and land uses were separated by inflexible zoning codes. More than just discouraged, pedestrian activity became next to impossible. Where it [Page 1342]did occur, the dangers incurred by traversing the streetscape on foot were daunting.

Efforts to mitigate the risk factors associated with pedestrian travel are frequently associated with the concept of traffic calming. Encompassing a series of design principles, the primary objective of traffic calming is the reduction of automobile speed and volume along residential streets.

Traffic calming devices may fall under the following four broad categories based on their design. First, vertical deflections are elevated sections of roadway that force drivers to slow down. A common type of vertical deflection is the speed hump, which is a raised area in the roadway pavement extending across the entire road. Raised crosswalks and speed tables also serve as examples of vertical deflections. Second, horizontal deflections, a second category of calming, alter the street width to discourage through traffic and reduce traffic volume. Chicanes are a common approach to horizontal deflection and are created by building out curb lines. Roundabouts and traffic circles also serve as horizontal deflections on busier streets. Third, narrowings are roadway segments that are narrower than the overall width of the street. One example is the “neckdown,” which is created by narrowing the street and widening the sidewalk. Fourth and finally, speed zoning is a section of street with a lower maximum legal speed than the limit for the rest of the roadway.

Additional traffic calming devices include the following: bus bulb, a widening of the sidewalk at a bus stop location so that buses remain in the travel lane when stopped at the bus stop; pedestrian refuge, a small island placed in the center of a two-way street that separates traffic and enables pedestrians to cross the street in stages; and roadway color/texture, the use of materials that introduce surface texture to the roadway, such as paver stones, bricks, or stamped asphalt.