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.

Traffic calming has its origins in the Dutch "Woonerf" schemes of the 1970s, and since then has been further extended and refined throughout northern Europe, particularly in Germany and the Netherlands. The original "Woonerf" schemes introduced the concept of shared space between vehicle and pedestrian. Streets were reconstructed so as to tip the balance in favour of the residential function of the street and to reduce the domination of motor vehicles. The wholesale reconstruction of streets required by the "Woonerf" was by necessity expensive, and since then this technique has been abandoned in favour of cheaper measures while still retaining the essential traffic calming concept. Traffic calming techniques are now applied to whole areas of towns and not just to individual streets. Main traffic arteries, villages, shopping streets and town centres have all been included. Area wide traffic calming schemes seek to calm both the main roads and the residential roads in an area so as to ameliorate the impact of any traffic transfer as a consequence of traffic calming. (Harvey, 1992)

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.

(Based on Trafficcalming.org, and complemented from Hass-Klau et al (1992) and IHT (1997))

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.

Traffic calming measures are not dependent on technology, but the 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.