Traffic is one of the main factors determining quality of life among city residents. Donald Appleyard, author of Livable Streets and a pioneer in community-based planning, performed studies in San Francisco in the late 1960s that clearly showed that traffic flows can influence the social interactions of residents along those streets. Over the years we have learned more about the particular impacts traffic has on neighborhood life, and developed ways to decrease the interpersonal impacts a street can have when it transects a neighborhood.
A growing number of cities have begun fighting to take back neighborhood streets from the traffic they carry by implementing programs loosely defined as "traffic calming." The overall idea is that instead of barring traffic from certain areas, roads can be designed so that cars behave in an appropriate way when they are on streets with a lot of pedestrian activity. Traffic calming centers around an idea that is part engineering and part behavioral psychology, and suggests drivers react predictably to certain road conditions. For example, on narrower streets people tend to drive slower and pay more attention.
But narrowing streets isn't the only way to calm traffic. Traffic circles are an effective way to slow traffic at intervals, while actually speeding up overall trip time because they remove stop signs. Speed humps are raised sections of the road that are only comfortable if they're driven over slowly, and are one of the least-expensive solutions (not to be confused with speed bumps, which require coming to a near stop to cross). Sidewalks can be "bulbed out," both providing a place for landscaping and making the street less of a straight throughway. Bulbouts (also called curb extensions) can also be used at corners to shorten the walk for pedestrians crossing the street. We can define traffic calming broadly to include all types of measures designed to reduce the impact of motor vehicles on livability in surrounding neighborhoods.
Many European cities have a long history of implementing traffic-calming measures and can provide lessons for cities seeking to implement or improve their programs. Some are introducing innovative techniques into their plans for managing traffic in the urban core, from making dedicated space for other modes of transportation to redesigning their streets.
As part of a research project, I discussed recent traffic calming projects and issues with planners in Zurich , Vienna , and Munich . European cities typically have broad experience implementing traffic calming and can provide lessons for U.S. cities seeking to improve and expand their programs.
Integration of Traffic Calming into Transportation Plans
Zurich , Vienna , and Munich have integrated traffic-calming into their general transportation-planning process and believe that it measurably improves transportation as well as livability. Zurich 's transportation plan, in place since the 1980s, promotes public transit, reduces motor vehicle traffic, channels traffic outside of residential areas, reduces parking, and encourages bicycling and walking. These goals recognize that the carrot of improved public transit and environmentally friendly transportation cannot alone ensure the city's quality of life--measures designed to reduce motor vehicle traffic such as traffic calming, traffic reduction, and commuter parking reductions are also needed.
Vienna's transportation plan1 calls for a reduction in private vehicle "mode split?--what percentage of the total trips taken in a city are by bus, bike, taxi, private car, or on foot--from 37 percent to 25 percent by 2010. The plan focuses on sustainable mobility, efficiency, public acceptance, cooperation between the city and region, and innovation. Of particular interest for traffic calming are goals to reduce use of private vehicles and encourage a shift to environmentally friendly modes, such as bicycling and transit.
Munich has made improvement of bike and pedestrian facilities a key point in its new transportation plan, which calls for reducing automobile trips by five percent and increasing bike trips by five percent while maintaining transit and pedestrian trips at current levels. These goals are part of Munich's comprehensive development plan, The Munich Perspective2 which presents the city's guiding development principles: "compact, urban, green"--compact to use urban land efficiently, urban to provide an attractive mix of homes, jobs, shops, and leisure facilities, and green because an attractive arrangement of open spaces and vegetation improves the natural balance and enhances the quality of urban recreation.
Public Support for Traffic Calming
Traffic calming measures can be controversial and most government agencies are controversy-adverse. Thus gaining public support is critical. Zurich , Vienna , and Munich are all implementing very comprehensive public involvement programs for traffic calming throughout the process from planning to implementation. Three particular strategies are expert commissions to evaluate techniques and programs, guided public involvement, and community partnerships.
Vienna organized an expert commission to evaluate traffic calming at the height of a public controversy over the program. This commission--known as the Ohrwaschel Kommission, since corner widenings look a bit like ears and Ohr is ear in German--included technical experts, business groups, advocacy groups (such as bicycle groups) and city administration, as well as--importantly--opponents to traffic calming (like automobile clubs). The commission approved almost 95% of the traffic calming improvements proposed such as sidewalk bulbs, increased pedestrian areas, and traffic regulations. Munich has used a partnership of businesses (including BMW) and community groups to co-operatively improve transportation. One program objective sums up the urban transportation problem, "the share of automobile transportation should shrink as you get closer to the center of the city." Making businesses and organizations part of the process has helped build understanding and support for traffic calming in Munich and Vienna .
Financing Traffic Calming
Funding constraints restrict traffic calming in both scope and strategy. Many cities are forced to implement inexpensive improvements even when they know other strategies would work better, and must address traffic calming on a spot-fix basis rather than through more costly but potentially more effective comprehensive plans.
A commonsense approach for reducing costs and impacts is to implement several projects concurrently. A good example is repairing underground utilities before repaving a street.
In Vienna , traffic calming improvements are implemented as part of the regular roadway maintenance program. Thus, when streets are re-paved, traffic calming measures are built concurrently. Often agencies responsible for street rehabilitation are so focused on paving that they are not motivated to add traffic calming. By linking funding for street rehabilitation to implementation of traffic calming, it is possible to provide the extra encouragement for otherwise reluctant city departments.
Zurich has also coordinated implementation of traffic calming with other programs and has used this approach to implement projects that might otherwise be unpopular. For example, it has paired implementation of a traffic calming project that reduces traffic through a neighborhood (viewed positively by residents) with a transit priority project that reduces parking (viewed negatively).
Traffic Calming on Arterials and Squares
Historically, the main concern of traffic calming has been reducing traffic in residential neighborhoods. Increasingly however cities are considering traffic calming for arterial streets and public squares. Since these are often neighborhood commercial streets, an important goal is economic--improving the environment to increase the attractiveness of the area's shops, cafes, and businesses.
Zurich has recently undertaken a comprehensive program to improve the livability and economy in its major squares while also improving their transportation functions. Zurich 's planners improved public transit by re-locating transit stops, fine-tuning transit priority while renewing streetcar track and stations. Traffic volumes were maintained while reducing the street space through careful channelization and traffic signal design. Vienna has also rebuilt streets to make them more livable by reducing road space and increasing pedestrian space as part of other projects.
Interestingly, several innovative traffic-calming improvements have been built that challenge traditional traffic engineering. For example:
Transit priority does not always require dedicated lanes. Zurich uses traffic signals to provide "transit priority" (the signals allow transit to get a head start over cars at intersections) on some one-lane streets, leaving room to expand sidewalks for cafes, shops, and people.
Removing bicycle lanes and narrowing streets can reduce vehicle speeds, improve overall traffic safety, and increase neighborhood livability, without significantly reducing motor traffic volumes. The idea is slow and constant movement rather than fast stop-and-go traffic.
Traffic signals can be replaced by roundabouts. These types of improvements require careful traffic engineering and close coordination between different city departments to implement successfully.
The more recent trend in European traffic engineering ideas is to actually remove signs and signals--and in some cases even sidewalks--to force drivers to pay more attention to the road for their visual cues, with a resulting drop in accidents involving pedestrians.3 An important point to take away from this is that by being open to thinking differently about how drivers will respond to different roadway configurations and uses, we can discover new ways of making the streets safer.
Drivers are more careful when the streets are narrow and when there is landscaping, like street trees and planted medians. Stop signs and speed bumps are more traditional additions to streets designed to make drivers more aware, but they are by no means the only ways to slow traffic. In general, the more we "automate" driving by giving drivers long notice before light changes, stops, and turns, the more certain they become that nothing will "jump out" at them, and so the less they pay attention. The more you separate the car-way from the people-way, in other words, the more dangerous a street can become. The less certain drivers are about road conditions, the closer attention to it they pay.
Loss of parking is a leading source of opposition to traffic calming, but parking control is one of the most effective ways to reduce congestion, encourage environmentally friendly transportation, and increase livability.
The main parking control measure is residential parking zones. Vienna 's program, which is very similar to San Francisco 's residential parking program, is based on areas. By preventing commuter parking in neighborhoods surrounding the center, Vienna has helped reduce the motor vehicle mode split by four percent while increasing public transit and biking mode split by two percent each. What's important about this finding is the understanding that parking control has influence on traffic and transit use; which means we need to focus on implementing new parking controls targeted towards reducing commuter traffic. One underutilized parking control measure is charging (closer to) market rates for parking.
Given the controversy over removing neighborhood parking for traffic calming improvements such as pedestrian zones, Zurich and Vienna have chosen to replace surface parking lost for traffic calming with underground parking. This represents a clear compromise, but removing cars from the surface provides real traffic calming and livability benefits, even if not as environmentally beneficial as simply eliminating the cars. Furthermore, since drivers must pay to use these garages it provides the cities with the opportunity to experiment with parking pricing.
Other European cities, including Paris , have taken a similar approach, building underground parking and introducing traffic calming with open space on the surface level. These facilities can also be designed to further reduce automobile impacts by carefully designing entrances and exits to feed traffic onto the major arteries.
Traffic calming has been well integrated into the general transportation planning process in many cities. It is no longer an idea on the periphery of traffic planning, but is viewed as a way to help meet traffic-reduction goals.
Unfortunately, adequate funding is not available for traffic calming in most cities. Funding shortages have forced cities to implement less-than-ideal techniques and have reduced their ability to implement more comprehensive programs. Therefore, cities are searching for less expensive ways to implement traffic calming and are linking traffic calming with other, better-funded programs, like street resurfacing.
Implementing traffic calming can be difficult technically, politically, and financially, but most cities are working closely with the community on implementation of traffic-calming projects. They work proactively using such techniques as partnership programs, citizen involvement, and expert commissions. This process has led to compromise on the policy and project level (such as replacing parking taken to implement traffic calming with underground parking), but has enabled many programs to progress. Finally, a new generation of projects is challenging the traffic-engineering orthodoxy.