Homebuyers Beware: Narrower Streets May Not Mean Safer Neighborhoods

FAYETTEVILLE, Ark. - A University of Arkansas researcher thinks that narrowing roads to produce more livable communities may not always have the desired effect. Contrary to currently popular planning theories, his research indicates that narrower streets may not always reduce traffic speed and may cause additional problems.

"If a high-volume street is narrowed, the resulting congestion may lower speeds," explains Jim Gattis, associate professor of civil engineering, "but it also may lead to increased noise and air pollution and driver frustration. And if driver frustration leads to more risk-taking, narrowing the street can also result in more crashes."

In a study recently published in the Journal of Transportation Engineering, Gattis looked at the relationship among urban street width, function and resulting speed. He also looked at accident data for the streets in question. The study was conducted in a small southern city with a population of 50,000. It contrasted various streets within a grid-layout neighborhood from the late 1800s with each other and with those from a neighborhood constructed in the 1950s-1960s and a neighborhood built in the 1980s-1990s.

One issue in urban planning is the unstated presumption that slower is always safer. Gattis’ study results also indicate that speed may not be as significant a factor in urban street safety as is generally assumed.

In examining accident rates on two adjacent, parallel through streets, Gattis found significant differences in accidents, but not speeds. Although one street was 50 percent wider than the other, speeds on these streets were essentially the same. However, accident rates on the narrower street were more than 50 percent higher and personal injury accidents were 25 percent higher than on the wider street.

Planners classify streets according to their intended use. Local streets should be short and meant for residential traffic. They typically connect to collector streets, which funnel traffic out of neighborhood and toward arterial streets. Arterial streets are intended to move through traffic from one area to another with minimal impediment. Problems arise when these principles are misapplied.

"City planners and elected officials who did not understand the need for various elements to complement each other have allowed residential lots to front arterial streets," Gattis explained. "Improper neighborhood design causes some streets intended to be local to instead function -- or malfunction -- as collector streets. Streets designed for a lower level of traffic actually end up carrying a higher volume."

A great deal of attention has been devoted to neighborhood design and traffic issues in recent years. Confronted by a steady stream of resident complaints about traffic, city planners and traffic engineers have responded by applying many types of traffic-calming techniques ranging from stop signs to speed bumps and rumble strips. Unfortunately, these methods may irritate drivers and produce undesirable secondary consequences, such as accidents and increased traffic noise.

One traffic calming technique that has been adopted by neotraditionalist designers is use of narrow streets to slow traffic. Supporters of narrower streets often make the assumption that wider streets always mean higher speeds. Gattis’ study suggests that the actual function of the street - the driver’s intent - not the just the width or the planned use, affects motorists’ speed.

"Street width may play a small role in vehicle speed," Gattis noted, "but other factors may be far more significant in determining actual through-traffic speed on any given street."

For example, one street in the study was nominally classified as a local street. It was relatively narrow with houses along both sides. However, because it acted as a cut-through street, speeds on it were higher even though the street was narrower than other streets in the study

Gattis also found speeds on all of the local streets varied by only 4 mph, even though some streets were more than 50 percent wider than others.This is exemplified by one street, which is six feet wider at one end than the other. Data show that when drivers entered the wider segment their speeds did not increase significantly.

By focusing on reduction of vehicle speed, planners, designers, neighborhood activists and homeowners may be missing a key issue in street design. Functional design, which recognizes and accommodates human nature, has been rejected by many designers in favor of approaches that attempt to adopt layout pattern concepts from the past.

"Traffic calming and neotraditional strategies attempt to force drivers to do what they would not otherwise do," explained Gattis. "In other words, instead of designing to accommodate the person, the person is supposed to adjust to a behavior mandated by the designer."

However, human driving behavior is not easily controlled. As Gattis’ study indicates, drivers will tend to use roads according to their needs, rather than the intent of the designer. Implementation of design components to force driver compliance may result in unintended and unwanted consequences, including increased risk-taking, traffic noise and accidents.

"Potential home buyers should consider street layouts and traffic patterns carefully before buying," Gattis counsels. "Even if a through street isn’t carrying a lot of traffic now, there is a good chance that it will some day as the area builds up."