An issue known as "traffic calming" has received considerable recent discussion in the traffic engineering profession. In the July 1997 issue of the ITE Journal, James R. Hanks, international president of ITE (Institute of Transportation Engineers), noted that people often view traffic calming as little more than an effort to fix earlier mistakes made in designing street patterns, particularly in residential areas. This is a misconception. Hanks indicated that these traffic calming patterns "are not so much 'mistakes' as they are a reflection of the changing desires of communities and society over time."

In an effort to clarify the meaning of traffic calming, in January 1997 the ITE International Board of Direction made traffic calming a "priority subject for the Institute." Both the July and August 1997 issues of the ITE Journal were devoted to the subject of traffic calming. In addition, a "significant portion" of the Institute's March 1997 conference in Tampa, Florida addressed this issue.

Much of this discussion about traffic calming revolved around the lack of, but obvious need for, a unified and universally accepted definition of the term. In the July 1997 issue of the ITE Journal, Ian M. Lockwood discussed this problem and its resolution in his article "ITE Traffic Calming Definition."

At the 66th ITE Annual Meeting in Minneapolis, Minnesota (September 1996), attempts to discuss traffic calming were hampered by the absence of a "common definition." As a result, a subcommittee was established to create a definition of traffic calming that would be broad enough for a variety of situations but specific enough to prevent confusion, improve communication, and allow for universal understanding and application. The subcommittee presented its findings and the following definition of traffic calming at the March 1997 conference in Tampa:

Lockwood noted that interpretations of the definition are as critical as the definition itself: "The interpretation is not only important to define what traffic calming is, it also determines what traffic calming is not. That is, if something is not included in the interpretation, then it is likely not traffic calming."

The "mainly physical measures" portion of the definition can be understood to mean "physical measures and a supportive environment, which includes such things as policy and legislative support for traffic calming and flexibility of standards, guidelines, and practices." The "reduce the negative effects of motor vehicle use" portion can mean altering both the design and role of the street to minimize the adverse effects (such as speeding and pollution) that vehicles can have on both individuals and society as a whole.

The "alter driver behavior" portion of the definition means drivers regulate their own behavior, such as reducing both their speed and aggressive driving and increasing their respect for pedestrians, bicyclists, etc. "Improv[ing] conditions for [these] non-motorized street users" means promoting activities such as walking and cycling, increasing overall safety, and enhancing aesthetics.

The "measures" referred to in the definition include a number of categories: vertical and lateral changes to the street, constrictions, narrow pavement widths, entrance features, traffic circles, small corner radii, and related "streetscaping," such as lighting, trees, landscaping, art, etc., placed along streets and at intersections. (Traffic calming is most successful when it is accompanied by streetscaping.) While these categories are specific, they are also flexible--allowing new measures to be added to any category.

In addition to these measures, traffic calming also involves a number of goals and objectives. These are also flexible, and allow traffic calming to be adapted for various situations, locations, street types, budgets, adjoining land uses, and community preferences. Examples of the goals include enhancing quality of life, creating streets that are both safe and aesthetically pleasing, and reducing negatives such as energy consumption and urban sprawl. Examples of objectives include reducing speeds, collisions, and the need for police enforcement and increasing safety for non-motorized street users. Both the goals and objectives "demonstrate that traffic calming involves much more than just motor vehicle issues."

Despite the overall flexibility of traffic calming, certain "criteria" must be met before a potential street modification project can truly be considered traffic calming. Traffic calming must:

• have its base in the community and be supported by it,
• include a measure by which drivers can self-enforce their own speeds,
• affect driver behavior directly, and
• improve the safety of all street users, in particular those who are "vulnerable," such as children and the elderly.

The new definition of traffic calming is an improvement over previous definitions that were either too broad or too narrow. However, with that improvement certain "initiatives, techniques, and policies" that were once considered a part of traffic calming have been displaced. To help avoid confusion about these displaced issues, definitions for the following related words and phrases were also created: traffic calming measures, route modification, traffic control devices, streetscaping, traffic calming plans, neighborhood traffic calming plans, area-wide traffic calming plans, route modification (or traffic management) plans, neighborhood route modification (or traffic management) plans, and street modification plans.

Traffic calming measures and route modifications have often been used interchangeably. They do share similar goals, but they represent different concepts. Traffic control devices are often incorrectly considered traffic calming measures. They too share the common goal of reducing driver speeds, but achieve that goal by different means.