TECHNIQUES FOR URBAN SUSTAINABILITY

Traffic Calming

BY JEFF KENWORTHY
Institute for Sustainability and Technology Policy, Murdoch University

Introduction

Traffic calming (from the German 'Verkehrsberuhigung') is the process of slowing down traffic so that the street environment is safer and more conducive to pedestrians, cyclists, residential life and shoppers. Traffic calming is best done by physically altering the street environment through different road textures, changing the geometry of the road through chicanes, neck-downs, speed plateaus and other traffic engineering devices, introducing new street furniture designed to create a more human, safe environment and by planting attractive landscaping. Together, these changes make drivers slow down by causing them to see less open black-top and to perceive the road as a space which is to be shared with pedestrians, cyclists and transit vehicles. Through the avenues of trees and street gardens which accompany good traffic calming schemes, urban wildlife habitats and corridors through cities can be created and soft surfaces can be increased so there is less storm water pollution. Traffic calming has the potential not only to lessen the direct negative impacts of road traffic, but to foster urban environments which are more human and interactive, more beautiful, and more economically successful due to the greater social vitality possible in a city's public spaces.

PHOTO 1 A traffic calmed inner city street in Freiburg showing the
strong landscape elements of good traffic calming schemes.

PHOTO 2 A traffic calmed precinct in Frankfurt's Bockenheim district

It is not known exactly where or when the concept of traffic calming originated, but the German term is believed to have first been quoted in Federal German Government reports in the early 1970s. The late John Roberts of Transportation and Environment Studies (see TEST, 1989) in London was the first to translate the word into English and to bring the concept to the attention of transportation planners in other parts of the world. The idea of traffic calming however, has its roots in post-war trends towards protecting city environments from the worst excesses of the automobile. This reached a watershed in the early 1960s with the publication of the major report entitled 'Traffic in Towns' by Colin Buchanan (Minister of Transportation, 1963). Although the UK approach was to create more calmed city centres and protected residential precincts, the Buchanan report was used mostly to build large ring roads and bypasses which helped create automobile dependence. The report was used to justify major road proposals in Australian and North American cities as well. However, the European approach is more based in the organic integrity of the urban street and this approach is now gaining currency in the UK (SACTRA, 1994, Department of Environment, 1986).

Traffic calming emerged in Europe in the late 1960s from a number of sources: the Dutch Woonerf or 'Living Yard' created streets that had one shared surface with much planting to slow speeding traffic through inner city streets and the original pedestrianisation schemes in cities like central Copenhagen (Gehl and Gemsoe, 1996). Traffic calming gained rapid growth and acceptance in Europe in the 1980s through the successful action of many environmental groups trying to curtail the impacts of the automobile on European cities. More detail on the evolution of traffic calming can be found in Hass-Klau (1990a), Tolley (1990) and Newman and Kenworthy (1991).

PHOTO 3 A Dutch Woonerf in the city of Groningen.
The Woonerf was the original form of traffic calming which started in this city in 1968.

PHOTO 4 The pedestrian zone in central Copenhagen remains
one of the world's greatest success stories in pedestrianisation.

Traffic calming's major objectives are to:

• reduce the severity and number of accidents in urban areas;

• reduce, local air and noise pollution and vehicle fuel consumption;

• improve the urban street environment for non-motor car users;

• reduce the car's dominance on roads by reclaiming road space for living space;

• reduce the barrier effects of motor traffic on pedestrian and cycle movement and;

• enhance local economic activity by creating a better environment for people.

With these broad objectives, traffic calming can also be of benefit to urban regeneration, housing renovation schemes and city beautification schemes (eg Freiburg in southern Germany). These assist more deeply in reducing automobile dependence by bringing urban activity back to areas of the city that are inherently less dependent on the automobile (ie denser central and inner areas of cities built more around transit and non-motorised modes). Traffic calming in Germany was in fact pioneered and promoted much more aggressively by the housing and urban development ministries than by the transportation ministry. This was primarily because of the positive impact traffic calming can have on the character and environmental quality of neighbourhoods, making them much more desirable urban redevelopment and residential areas, while a significant number of transportation planners viewed traffic calming changes with suspicion (Hass-Klau, 1990a).

PHOTO 5 A traffic calming project in the German city of Nurnberg that has
assisted in revitalisation of the surrounding residential areas.

Techniques of Traffic Calming and Their Implementation

Traffic calming was originally restricted mainly to improving residential streets and this is still a major focus. Traffic calming seeks to alter road layout and design without actually totally rebuilding a street system. It does this through a whole suite of possible techniques such as narrowed entries to streets, planting of trees with a strong vertical element, variable street surfaces, speed tables, rumble strips and so on (see Box 4.2). These are now well-documented and illustrated in many detailed publications (eg City of Frankfurt, 1990; Pharoah, 1990; Tolley, 1990; Toyota Motor Corporation, 1990; Hass-Klau, 1990c; Danish Roads Directorate, 1981; Brindle, 1997). However, it has been recognised that to be really effective and to not just shift traffic problems from one area to another, traffic calming must be applied more on an area-wide basis (Hass-Klau, 1990b), which means involving arterial or main roads.

There are now many examples of traffic calming on through-roads and in other busy areas throughout Europe (eg Frankfurt, Hamburg, Nurnberg, Berlin and Copenhagen). Denmark has a specific nationwide programme of traffic calming on main roads called Environmentally Adapted Through Roads (Danish Road Data Laboratory, 1987, 1988).

PHOTO 6 A main road in the suburbs of Copenhagen that has been traffic calmed from 4 lanes to 2 lanes of traffic.

PHOTO 7 and 8 A main street in the Eppendorf area of Hamburg showing
how a 4 lane road can be reduced to 2 lanes with a large increase in amenity

The approach to traffic calming has to be somewhat different on main roads because of the volumes of traffic involved, although there is overlap in the basic techniques used. In busier areas where there is a need to better balance the needs of motor vehicles with the needs of pedestrians and cyclists, the main goal is to be able to reclaim road space for other uses by reducing the speed of traffic and its impact. In most cases roads are simply reduced from say 6 to 4 traffic lanes or 4 to 2 lanes through critical areas of a city. The potential benefits of traffic calming on main roads is summarised by Hajdu (1988) in his description of the transformation of a 1.3 km main route in the inner area of Hanover:

"The city changed that road from an overloaded artery to a thoroughfare with a series of streetscapes, some with narrowed carriageways. The changes included footpaths containing trees, others fully pedestrianized with fountains, outdoor cafes, and a weekly market. The city resurfaced adjacent residential streets and limited access to residents' cars."

In some cases the reductions in road space are accompanied by significant improvements to transit such as new rail links (eg Nurnberg) and in others no major changes are made but incremental improvements are implemented. Road capacity is not necessarily reduced because the loss of lanes is offset by slower speeds which reduce vehicle headways and enable more vehicles to pass. Similarly, parking supply is not necessarily reduced and in some cases may be increased nominally. Often, parallel parking on two sides of a road is converted to angle parking on alternate sides separated by chicanes.

PHOTO 9 A residential street in Christchurch, New Zealand after being
treated with traffic calming. This was a resident-based initiative.

PHOTO 10 and 11 In Portland, Oregon, traffic calming has been undertaken in
conjunction with implementation of LRT and radical urban design changes, with excellent results.

The implementation of traffic calming, however, is not just a technical process but a wide ranging community process whereby local residents can have a strong input into identifying the problems and helping to find the solutions. It has been repeatedly shown that good public consultation and involvement of the community is essential to the widespread acceptance of traffic calming schemes. In fact an important advantage of traffic calming is the way it has been able to provide a focal point for mobilising and galvanising many communities around the world into developing and fighting for a vision of a more sustainable and socially acceptable solution to the problem of traffic in urban environments (eg Tolley, 1990).

Effects Of Traffic Calming Schemes

Many of the major traffic calming schemes in Europe have been formerly sponsored by Federal and local governments as demonstration projects and one of the aims has been to test the effects of the traffic calming schemes on key environmental indicators and safety factors. Much of the available evidence about the effects of traffic calming schemes has come from before and after studies of these projects.

The following is a brief summary of the general effects of traffic calming schemes with some specific examples:

Reduced Accidents

Accidents, particularly the severity of accidents, are generally significantly reduced with traffic calming because speed is the most critical factor in road accidents particularly the risk of serious injury and the danger to pedestrians and cyclists. In Berlin for example, the area-wide scheme resulted in the reductions shown in Table 4.1.

Most other schemes report similar kind of data such as in Heidelberg which experienced average accident reductions of 31% and a 44% reduction for casualties after 30km/h residential speed limits were introduced along with selected physical traffic calming measures (Hass-Klau, 1990d). The area-wide schemes in the Netherlands have reduced accidents involving injury by 50% in residential areas and 20% overall (measured per million vehicle km) and no increase in accidents has occurred in surrounding areas (Hass-Klau, 1986).

Source: Reported in Pharoah and Russell (1989)

The Centre for Liveable Communities in their Liveable Places Update for March 1998, summarised some of the best US examples of traffic calming and in relation to accidents found the following:

The City of Seattle, where traffic calming projects have been carried out for 20 years, surveyed the results of 119 completed projects and found an overwhelming 94% reduction in accidents.

In Portland, Oregon, 70 traffic circles and 300 speed bumps have been introduced and the number of reported accidents went down by 50%.

A 1997 study of US street typology and accidents by Swift and Associates showed that as street width widens then accidents/mile/year increase exponentially. The safest residential street (curb to curb) turned out to be 24 feet (7.2 metres). Present US street regulations require 36 feet, primarily for access by fire vehicles, through the study found fire vehicles can access 24 feet roads when required. New Urbanism design guidelines are for 24 feet roads (see section 6).

PHOTO 12 Reducing road trauma is an important part of traffic calming schemes.
This is part of a British campaign to implement traffic calming in residential areas.

Noise

Traffic calming generally results in a reduction in vehicle noise. Pharoah and Russell (1989) report that noise changes result from five factors:

- changes in volume and composition of traffic

- changes in carriageway layout

- changes in carriageway surface

- changes in vehicle speed

- changes in driving style

Air pollution

Research in central Europe shows that in built up areas, the higher the vehicle speed the more will be the proportion of acceleration, deceleration and braking and this increases air pollution. By contrast, traffic calming schemes in some German residential areas have indicated that idle times are reduced by 15%, gear changing by 12%, brake use by 14% and petrol use by 12% (Hass-Klau, 1990a).

Evidence for the air pollution benefits of a slower, calmer style of driving comes from detailed work in Buxtehude, a German demonstration project (pop. 33,000). Table 4.2 shows the changes in the different types of emissions with a reduction of speed from 50 km/h to 30 km/h under two types of driving. In both aggressive and calm driving, emissions are reduced at the 30 km/h level, though the calm driving has a generally greater reduction and fuel use is lower.

SOURCE: Reported in Pharoah and Russell (1989) from German research.

It is also worth noting that even in instances where individual vehicles may experience an increase in fuel and emissions (eg drivers do indulge in more acceleration, braking and greater use of second gear), this may not result in an overall increase in local pollution and fuel use if the traffic calming scheme has also resulted in lower traffic volumes.

Pedestrian and street activity

Traffic calming seeks to make the public environment safer and more attractive so it is to be expected that traffic calming will result in a greater level of pedestrian and cycle activity in the area treated. In general, it can be expected that the results will be more noticeable in busier areas with a mix of land uses and the potential for people to actually make good use of reclaimed areas such as outdoor eating and trading areas, childrens' facilities etc.

PHOTO 13 In Groningen, the city centre is accessible independently by all people
due to Groningen's progressive policies on traffic calming and pedestrianisation.

Some formal measurements of the benefits are available from a summary of European experience by Pharoah and Russell (1989) such as in Berlin's Federal demonstration project where non-motorised traffic on a wide range of streets in the scheme increased by between 27% and 114%, in Vinderup, a village in Denmark where the main through route was traffic calmed and outdoor activities increased by up to 47% and in Copenhagen where traffic calming has led to immediate increases of pedestrian activity of between 20% to 40% and in the long term where central area activity is now 80% pedestrian and 14% by bike (Gehl and Gemsoe, 1996). Where the traffic calming reduces road capacity there is an overall decrease in traffic (Goodwin, 1988) and hence better conditions are created for pedestrians.

Traffic calming also tends to increase the area used by pedestrians and cyclists and the extent to which streets are crossed by these users, as severance effects of traffic are reduced. Pedestrians and cyclists tend not to confine themselves purely to walkways but rather they extend their territory to the carriageway in some instances.

PHOTO 14 In Frankfurt's Bockenheim districts, pedestrians cross the street
at will due to the slow speed of traffic and the friendly pedestrian environment.

Reduced crime rates

Appleyard (1981) showed that visiting among neighbours decreases when traffic increases and when neighbouring ceases and people stop watching out for one another, then criminal activity can occur. The Liveable Places Update (March 1998) overview on traffic calming quotes a Harvard University study that showed violent crimes in communities where residents willingly worked together were as much as 40% lower than in neighbourhoods where such relationships were not as strong. Race and income were not factors in people's willingness to take part in such community activity. Examples of places where crime rates diminished after traffic calming include Weinland Park in Columbus, Ohio.

Economic implications

As pointed out in the objectives of traffic calming, economic revitalisation of an area is an explicit aim in some schemes.

A study by TEST (1989) attempted to confirm the hypothesis that "A good physical environment is a good economic environment" and examined ten cities in Europe in detail. Roberts (1988) sums up the work by saying that:

"...the message is simple: there is a strong likelihood that traffic restraint in all its forms, and environmental improvement, and a healthy economy, are causally related." (p. 141)

The basis of this would appear to involve at least the following factors:

a) people like to come to humanly attractive, green cities;

b) businesses like to locate in areas with a high quality urban environment;

c) car access is not banned but it is not facilitated to the point of dominating everything else;

d) other modes are generally facilitated.

Hass-Klau (1993) shows conclusively that pedestrianisation and traffic calming both have positive effects on the economic performance of an area; the more aggressive is the traffic calming, the more pronounced is the positive economic effect.

In the US a West Palm Beach, Florida neighbourhood was economically depressed and bisected by fast moving traffic. A traffic calming scheme slowed the traffic through narrowing, building islands, humps and circles. Then the city raised intersections, levelled sidewalks with the street and added a fountain, benches and an ampitheatre for 'block parties'. The development spurred new private investment and commercial space rapidly moved from $5/square foot to $25/square foot (see Liveable Spaces Update, March 1998).

PHOTO 15 Economic activity booms along a street in Hamburg under a strong traffic calming strategy.

Traffic Calming: A Broader Approach

It is important to note briefly that traffic calming can be viewed as a broader transportation planning philosophy, and not merely as a series of physical changes to roads (Hass-Klau, 1990a). Traffic calming in this broader sense is aimed at reducing total dependence on the automobile and promoting a more self sufficient community with a transportation system more orientated to pedestrian, cycle and transit use.

These broader objectives can be summarised as follows:

a reduction of average motor vehicle speeds to discourage long distance road travel in urban areas and promotion of a more compact urban form; traffic calming of main roads is included in this approach;

specific land use policies which better integrate transit and land development; the policies are directed at reducing the number, length and need for motor vehicle trips;

strong promotion of walking, cycling and transit;

restrictive measures against private traffic including parking restrictions, limited major road building and the direction of funds into transit and non-motorised modes, taxation policies on fuels and cars including policies on company cars and road pricing;

a shift in transportation planning philosophy from a traffic generation approach of seeking to predict future traffic levels and the roads and parking needed to cope with them, to a traffic 'dissolving' approach of setting limits on motor vehicle growth and ensuring transportation/land use policies and practices are aimed at minimising the need for more motor vehicle facilities.

A good example of a broader traffic calming policy in action is the Dutch official national policy from 1982 which openly promotes transit, walking and cycling. It states that:

"Henceforth other functions will be given priority over motor traffic [and] the car's dominance should be diminished by deliberately increasing travel times, by creating a less dense network of main roads, and by reducing speeds" (Ministry of Transportation and Public Works, 1982).

PHOTO 16 It is important to remember the broader picture in traffic calming and that is the development of land use patterns that are pedestrian and bicycle-friendly and which do not require a car.
This has been achieved, for example, in False Creek in Vancouver.