Traffic calming is a way to lower traffic speeds or volume using physical measures. Traffic calming creates physical and visual cues that induce drivers to travel at lower speeds and is intended to be 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, and without enforcement. While added elements such as landscaping and lighting do not force a change in driver behavior, they might supplement the visual and perceptual cues that encourage people to drive more slowly. Slower motorist speeds help reduce the severity and number of crashes and help bicyclists feel more comfortable cycling in traffic.
Traffic diversion uses physical measures to restrict or divert traffic, typically to reduce cut-though motor vehicles, while not blocking local access. Traffic diversion measures may be used if other traffic calming measures do not sufficiently slow vehicles or reduce cut-through traffic. Often the tools of traffic calming and diversion are complementary and are used together. Ideally, streets would be designed and built for the desired travel speed and volume. Unfortunately, many existing local and neighborhood streets that should have slow design speeds and carry only local traffic were not designed to reflect this priority.
Traffic calming is such a powerful and compelling tool because it is very effective if properly applied. Some of the effects of traffic calming, such as fewer and less severe crashes, are clearly measurable. Other outcomes, such as enhanced community livability, are less tangible, but are also important.
Bicyclists deserve special consideration when planning, designing, and implementing traffic calming and diversion measures. Roadway narrowing or vertical or horizontal deflections of traffic to slow vehicles may have adverse impacts on bicyclists unless carefully done. Thoughtfully designed and used traffic calming measures, on the other hand, are valuable tools to enhance bicyclist safety and access. When traffic diversion is used, bicyclist and pedestrian access must be maintained. Typically, traffic calming and diversion measures are most appropriate on local streets that should have low speeds based on residential or intense commercial land uses. Traffic calming measures may also help to reduce traffic volumes on residential streets, where children and casual cyclists ride and other activities are carried out.
There are also some circumstances where traffic calming measures may be effective tools to enhance bicyclist safety and access on collector and arterial streets – those meant to carry higher volumes of traffic at higher speeds. These situations will be discussed under the individual countermeasures.
Traffic calming and diversion should be implemented and evaluated on an area-wide basis to avoid "diverting" problems to other streets or neighborhoods. It is also imperative to involve the community and all stakeholders in the process.
Other Internet resources on traffic calming: