University of California Transportation Center

Transportation and land use planners generally agree that high traffic volumes are incompatible with a good residential street. Danger to pedestrians and bicyclists and emissions from traffic, such as high noise levels and poor air quality, are the obvious reasons. In addition, traffic is also a barrier to social interaction. In 1969, Donald Appleyard demonstrated that residents living on streets with high traffic volumes are likely to have fewer friends and acquaintances among their neighbors, socialize less in their neighborhood, and identify less with their street as home territory than residents of streets with lower traffic volumes. He found that residents on high volume streets withdraw from the physical environment of the street and do not care for it.1 After studying 21 residential streets with a wide range of traffic volumes, he concluded that the quality of residential street life starts to diminish when daily average traffic volumes exceed 8,000 cars.2 Evidence of the detrimental effects of traffic on neighborhood livability has been compelling, and transportation planners have made it their goal to divert high volume through-traffic from residential streets whenever possible. Many cities have implemented traffic management plans designed to tame traffic on residential streets. Such plans created protected neighborhoods by routing non-local traffic along arterial streets.3 According to these plans, through-traffic was directed to commercial areas or other non-residential land uses, but with limited success — most medium to high volume streets in existing cities are also residential streets. In the inner city neighborhoods of San Francisco where Appleyard carried out the initial study, more than 75 percent of all streets with 8,000 cars or more per day also serve predominantly residential land use. In communities with lower densities, the percentage of medium to high volume residential streets is even greater.