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International Idea Exchange

Traffic Calming

Don Sheffield OAM
Emeritus Member and former CEO of IPWEA

Editor’s Note: This article is presented as part of the partnering agreement in place between APWA and its Australian counterpart, the Institute of Public Works Engineering Australia (IPWEA). The APWA International Affairs Committee has proposed these articles to assist in the transfer of information between our international partners.

Local Area Traffic Management (LATM) and Traffic Calming are tools that have been in use in Australia since the early 70s. They were introduced to encourage safer and more environmentally acceptable use of the road system by vehicular, pedestrian, and bicycle traffic. A key objective is to encourage that traffic to operate in a manner consistent with the adjacent land use planning and the intended function of the street network.

It is essential to understand that a street may serve many functions to a greater or lesser degree and that some of those functions may appear to be somewhat incompatible. Some of the functions of a road are:

Vehicular access to properties

Vehicular access within or through an area

A means of social interaction within a neighborhood

A play area or community open space

Access for emergency and service vehicles

Contributing visually to the living environment

The delivery of essential services such as water, power, lighting, gas, phone, etc.

The planning of the road network needs to consider these often-competing uses, and the development of a road hierarchy and a land use plan are required to achieve the proper balance.

The other essential ingredient is to recognize that community input into the process is vital. The process demands thorough research and concentration on satisfying the needs of the customer, not the manufacturer-whether these needs be real or imagined.

Pressure from Councils and local communities to obtain relief from unwanted traffic intrusion has increased over the past three or four decades. Traffic flows continue to increase and the community’s expectations for its quality of life have also grown. As traffic demand increases on the arterial roads, drivers often use the local roads to avoid the congested areas. This intrusion causes erosion of amenity to residents. This may create the catalyst for considering a scheme, but all issues must be identified before adequate measures can be introduced to address the problems.

Objectives that might form the basis of a scheme could include but should not be limited to:

Improving safety for motorists, pedestrians, and cyclists

Improving the operational environment of the street network

Reducing vehicular volumes

Reducing heavy vehicle traffic

Reducing traffic speeds

Reducing traffic noise

Improving the streetscape

Creating pedestrian areas

Creating additional play areas

The techniques that might be used to achieve these objectives will usually be drawn from:

Regulatory Measures

Signs and markings

Road closures, one-way streets

Light traffic roads

Traffic signals

Designated speed controls

Vertical Displacement Measures

Humps, bumps, and rumble strips

Thresholds

Paving block pavements

Horizontal Displacement Measures

Chicanes

Roundabouts (traffic circles)

Intersection controls

Pavement narrowing

Traffic islands and medians

Other Measures

Landscaping

Safety fencing

Pedestrian crossings

Lighting

The extent of the measures is really only restricted by the imagination of the designer and the acceptance of the users. Provided of course that sound engineering practice and common sense are applied to ensure the safety of all users of the street system is not compromised.

A common question asked is, “How will I (the designer) limit my liability if I construct any of these devices and accidents occur?” This is a complex question because of the innovative nature of the techniques often used. The answer lies in accepting the principles that govern most engineering activities. That is, using common sense and following accepted practices wherever possible.

Most of the treatments have been in use in various parts of the world for many years and guidelines have been developed for their use. Also, it is important to involve police, traffic experts, and the road authority in the planning and to use their collective experience to achieve the desired result.

It was suggested that part of this article focus on roundabouts or, as I understand they are known in the U.S., traffic circles.

These devices have been used in various parts of the world for many years in place of traffic signals. In this role they can be more costly to install, but are far more economical to maintain. They have achieved good results in reducing serious accidents by almost eliminating head-on collisions. They will effectively cope with high traffic volumes, provided that the flows in the entries are fairly uniform and they can reduce the delays sometimes caused by signals.

The design of the entry speed is critical to their success and this speed must be kept as low as possible in keeping with the sight distance available. Pedestrian access can be a problem as the well-designed roundabout will allow traffic to keep moving and this restricts the opportunities for pedestrians to cross the intersection. If pedestrian facilities have to be included, this can sometimes adversely affect the traffic flow through the roundabout.

Roundabouts were initially installed to facilitate traffic flows through intersections on roads carrying moderate traffic flows, but now they are often used in local streets as traffic calming devices. They are generally more acceptable to the community than speed humps and, along with controlling vehicle speeds, they assist in regulating flows through intersections.

Roundabouts in local streets require the same careful design of those in more highly trafficked streets to control the speed of vehicles through the intersection and to provide for the movement of larger service and emergency vehicles. They can cause difficulties for the designer in the collection of stormwater and the location of underground and overhead utility services.

They remain, however, as one of the most effective tools for the traffic engineer when considering LATM and traffic calming treatments.

Further information on the IPWEA can be obtained by visiting its web site at www.ipwea.org.au and on this topic by e-mailing the author at donsheffield@bigpond.com.