Summary

Traffic calming is the use of physical and regulatory measures to reduce vehicle speeds and acceleration. Its other aims are to alter driver behaviour and improve conditions for non-motorised street users. It focuses upon improving neighbourhood safety, comfort and liveability, whilst 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 concept originated in the Dutch ‘Woonerf’ schemes of the 1970s when individual streets were reconstructed to tip the balance in favour of a residential function of the streets and to reduce the domination of motor vehicles. Since then traffic calming has been extended to numerous countries (particularly in northern Europe, Australia and North America) and used not only for particular streets but also across whole areas, e.g. city centres.

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.

A combination of segregation measures can create a ‘maze’ or ‘labyrinth’, which makes through movement difficult (e.g. median barriers, one-way streets). 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 residents whom they are designed to benefit.

Integration measures are designed to encourage the driver to drive more slowly and cautiously. By making routes through residential areas slower, they can have a more direct impact on speed and hence safety, but will also induce re-routing to major roads, and hence a reduction in environmental impact. Such benefits may again be offset by increases in congestion and environmental impacts on the diversion route.

The evidence from case studies suggests that traffic calming is particularly effective in improving the ‘liveability’ of streets, providing additional protection to the local environment and reducing the incidence and severity of accidents. It is less effective in improving efficiency and stimulating economic growth but the overall trade-off would suggest a positive outcome from the implementation of traffic calming measures providing they have been carefully designed.