Traffic calming is a set of strategies used by urban planners and traffic engineers which aim to slow down or reduce traffic, thereby improving safety for pedestrians and bicyclists as well as improving the environment for residents. Calming measures are common in Europe, especially Northern Europe; less so in North America.
Traffic calming was traditionally justified on the grounds of pedestrian safety and reduction of noise and local air pollution which are side effects of the traffic. However, streets have many social and recreational functions which are severely impaired by car traffic. The Livable Streets study by Donald Appleyard (circa 1977) found that residents of streets with light traffic had, on average, three more friends and twice as many acquaintances as the people on streets with heavy traffic which were otherwise similar in dimensions, income, etc. For much of the twentieth century, streets were designed by engineers who were charged only with ensuring traffic flow and not with fostering the other functions of streets. The basis for traffic calming is broadening traffic engineering to include designing for these functions.
There are 3 "E"'s that traffic engineers refer to when discussing traffic calming: engineering, (community) education, and (police) enforcement. Because neighborhood traffic management studies have shown that often it is the residents themselves who are contributing to the perceived speeding problem within the neighborhood, it is stressed that the most effective traffic calming plans will entail all three components, and that engineering measures alone will not produce satisfactory results.
A number of visual changes to roads are being made to many streets to bring about more attentive driving, reduced speeds, reduced crashes, and greater tendency to yield to pedestrians. Visual traffic calming includes lane narrowings (9-10'), road diets (reduction in lanes), use of trees next to streets, on-street parking, and buildings placed in urban fashion close to streets.
Some additional traffic calming techniques that are often used are speed humps, speed cushions, and speed tables. These devices vary in size based on the desired speed. Humps, cushions and tables slow cars to between 10 and 25 miles per hour. Most devices are made of asphalt or concrete but rubber traffic calming products are emerging as an effective alternative with several advantages.
Types of traffic-calming engineering measures
Traffic calming can include the following engineering measures:
- Narrower traffic lanes — streets can be narrowed by extending the sidewalk, adding bollards or planters, or adding a bike lane or parking. Narrowing traffic lanes differs from other road treatments by making slower speeds seem more natural to drivers and less of an artificial imposition, as opposed to most other treatments used that physically force lower speeds or restrict route choice.
- Speed bumps, sometimes split or offset in the middle to help emergency vehicles reduce delay
- Speed humps, parabolic devices that are less aggressive than speed bumps and used on residential streets
- Speed tables, long flat-topped speed humps that slow cars more gradually than humps
- Speed cushions, a series of three small speed humps that slow cars down but allow emergency vehicles to straddle them so as not to slow response time
- Chicanes, which create a horizontal deflection causing vehicles to slow as they would for a curve
- Raised pedestrian crossings and raised intersection
- Curb extensions (also called bulbouts) which narrow the width of the roadway at pedestrian crossings
- Pedestrian refuges or small islands in the middle of the street
- Median diverters to prevent left turns or through movements into a residential area
- Changing the surface material or texture (for example, the selective use of brick or cobblestone)
- Additional give way (yield) signs
- Converting one-way streets into two-way streets
- Chokers, which are curb extensions that narrow the roadway to a single lane at points
- Allowing parking on one or both sides of a street
- Converting an intersection into a cul-de-sac or dead end
- Boom barrier, restricting through traffic to authorised vehicles only.
- Closing of streets to create pedestrian zones
- Reducing speed limits near institutions such as schools and hospitals
- Vehicle activated sign, signs which react with a message if they detect a vehicle exceeding a pre-determined speed.
- Watchman, traffic calming system
Recent trends in North America
Traffic calming has been successfully used for decades in cities across Europe. More recently, in response to growing numbers of traffic accidents and speeding problems, cities across North America have begun creating traffic calming programs to improve safety and liveability on residential streets. Many municipalities create asphalt or concrete measures, although preformed rubber products that are easier to install and consistently meet standardized requirements are becoming increasingly popular.
A living street
(sometimes known as Home zones
or by the Dutch
, as the concept originated in the Netherlands
) is a street in which the needs of car drivers are secondary to the needs of users of the street as a whole; traffic calming principles are integrated into their design.