Taxonomy and description
Terminology
Description
Technology

Terminology

The ITE (Institute of Transportation Engineers) Subcommittee on Traffic Calming states that "Traffic calming is the combination of mainly physical measures that reduce the negative effects of motor vehicle use, alter driver behavior and improve conditions for non-motorized street users". (Trafficcalming.org)

Traffic calming focuses on improving neighbourhood safety, comfort and livability, while maintaining necessary levels of traffic circulation and emergency access. It encompasses a broad array of traffic engineering, education, and enforcement techniques to slow and disperse or re-route traffic.

The solutions proposed to reduce the traffic speeds and volumes and favour the non-motorised modes have been refined with time. If early traffic calming measures (used in the 1980s -1990s) focused more on the laws of physics and applied to one or few streets, the more recent applications rely more on human psychology (intend to influence the driver’s ‘state of mind’ and generate a responsible-informal behaviour) and have the tendency to extend to large areas or to be applied differently according to the characteristics of each city area. The more recent understanding of traffic calming has often materialised in the design and development of ‘shared spaces’ and operates on the principle that all transport modes must equitably share the given street space, thus resulting in priority for pedestrians and cyclists. Examples of shared spaces are:

• the Dutch ‘woonerf’ – the shared space ‘pioneer’ developed in the 1970s and followed by different versions developed in northern Europe, among them the  British “home zone”
• the Swiss ‘Begegnungs­zonen’ – in UK known as ‘encounter zone’ and in France as ‘zone de rencontre’
• the ‘Berner model’ – applied starting in the 1990s for some towns located within Bern’s peripheral premises

Though traffic calming refers mainly to physical measures and devices altering streets’ configuration for the purpose of slowing motorised traffic, it now includes any measure/initiative that slows traffic and pushes pedestrians and cyclists onto the roadway while making the drivers more aware of their presence. Examples include inexpensive and easy-to-implement measures, related to temporary alterations or additions to the street appearance or temporary changes in its use such as:

• painting designs or patterns on the street (traffic circles, crosswalks, etc.);
• placing artworks, furniture or other objects in the middle of the roadway;
• coating the roadway in a rough surface;
• changing the colour or design of building enclosures and façades;
• temporarily changing the use of parking spaces or the roadway.

Reducing speed limits to 30km/h (or 20mph) is often used as a means of traffic calming, but is principally introduced to improve safety and is covered under accident remedial measures.

Traffic calming measures can be separated into two types based on the main impact intended:

• segregation (volume control measures), in which extraneous traffic is removed;

• integration (speed control measures), in which traffic is permitted, but encouraged to respect safety and the environment.

Trafficcalming.org summarise these measures in the following table. Other individual measures are reviewed in Hass-Klau et al (1992) and IHT (1997) as well as in UK Local Transport Note 1/07 (2007).

(Based on Trafficcalming.org, and complemented from Hass-Klau et al (1992) IHT (1997) and Local Transport Note 1/07) (Note that US and European terminology may differ.)

A combination of segregation measures can create a 'maze' or 'labyrinth', which makes through movement difficult. Their primary purpose is to discourage or eliminate through traffic and hence divert it to surrounding streets. The extra traffic on surrounding streets can add to congestion and environmental intrusion there, and this trade-off needs to be carefully considered at the design stage. However, the maze treatment also reduces accessibility for those living in the area, and this loss of accessibility has often led to the rejection of such measures by the residents whom they are designed to benefit (McKee and Mattingly, 1977). An alternative approach, more often used in city centres, is the traffic cell, in which an area is divided into cells, between which traffic movement, except perhaps for buses and emergency vehicles, is physically prohibited.

Integration measures are designed to encourage the driver to drive more slowly and cautiously. They can be divided into three groups: vertical deflections, horizontal deflections and narrowing. It is clear that these can achieve significant reductions in speed and accidents (Abbott et al, 1995; Barbosa et al, 2000). By making routes through residential areas slower, they can also induce re-routing to major roads, and hence a reduction in environmental impact (Sumner and Baguley, 1979). Such benefits may be offset by increases in congestion and environmental impact on the diversion route.

In contrast to the traffic control measures implemented in the 1980s, ‘shared space’ is achieved by removing all traffic signs, lights and other traffic control devices from the street space. The former are replaced by a streetscape that “speaks” to the driver through surface materials, building enclosure, on-street parking, trees and shrubs, art and decoration. Thus, the daily traffic is regulated by informal social-street rules and responsible travel behaviour. The aim of this approach, developed by the Dutch engineer Hans Monderman, is to enable common use of the available street space. In brief, the shared space concept rests on the idea that taking away traffic regulation elements generates a certain feeling of insecurity, which is assumed to lead to a higher attention level and thus to safer street user behavior.

Technology

Traffic calming measures are not dependent on technology, but some categories of vehicles such as buses and emergency vehicles may need protected access into a physically restricted area. Current access control technologies, which permit such vehicles to pass the point without stopping, are covered in regulatory restrictions.