To save lives, shift from arterial roads
The researchers’ findings bolster the argument that more of America’s transportation system ought to take the form of relatively narrow roadways lined by sidewalks — the kind of network that enhances public safety. The findings — which are based on a study of traffic accidents in metropolitan San Antonio from 2003 through 2007 — were presented by Dumbaugh during CNU-18 in Atlanta.
Arterial roads — wide roadways designed to carry large volumes of vehicular traffic, faster than on neighborhood streets — are associated with a 14 percent increase in collisions involving two or more vehicles, a 10 percent increase in vehicles running into pedestrians, and 8.4 percent more vehicle-bicyclist crashes, according to Dumbaugh.
The heightened danger, he explained, results from three factors: First, arterial roads encourage faster speeds, partly because they’re so wide. Second, they attract more vehicular traffic. Third, the many driveways along the arterials, which provide direct connections to businesses and parking lots, multiply opportunities for accidents.
Dumbaugh and Li correlated crash statistics from metro San Antonio with the size and configuration of land uses along the region’s roads. Among their findings:
• For every additional strip commercial use, there was a 2.4 percent rise in multiple-vehicle collisions. The speed of the vehicles entering and leaving the parking lots presumably accounted for many of the accidents.
• For each additional big-box store (a single-story building of at least 50,000 sq. ft., accompanied by a parking area at least that size), there was an 8.7 percent jump in multiple-vehicle collisions. There were also increases of 8.9 percent in vehicle-pedestrian crashes and 4.6 percent in vehicle-bicyclist accidents. The greater risk associated with big-box stores probably stemmed from the stores’ heavy traffic volume and from the extra-large parking lots the motorists had to navigate.
• When retail was scaled to pedestrians, the environment became safer. For each pedestrian-scaled retail use — occupying a building of no more than 20,000 sq. ft. that fronted the street or had little surface space devoted to parking — there was a 3.4 percent decrease in multiple-vehicle crashes and a 1.6 percent decrease in accidents involving vehicles and pedestrians.
• Denser development is beneficial from a safety perspective. Higher densities cut the number of vehicle miles traveled, which reduces the frequency of crashes. Higher densities also encourage urban development configurations, which also make crashes less numerous.
• Crashes of vehicles into fixed objects account for nearly a third of the nation’s traffic deaths, and these single-vehicle accidents are exacerbated by arterial roadways. A chief cause is high speeds; when the vehicle turns from the road onto a driveway or side street, the driver loses control and hits a utility pole or some other stationary object.
• “Traffic conflicts” (where one’s stream of auto traffic intersects with other traffic movements) also are common in traditional urban designs. But they are much less dangerous there because vehicles move more slowly on narrower urban streets.
Dumbaugh also examined how crash rates differ between arterial roadways and “livable streets” (historic main streets generally accompanied by street trees, street lighting, and pedestrian appurtenances. Per mile traveled, livable streets have 40 percent fewer midblock crashes and 67 percent fewer crashes overall.
Dangers to teens
Teen-agers in particular are placed in greater jeopardy by a sprawling form of development, says Dr. Michael Trowbridge of the University of Virginia. Trowbridge says teen-agers are much more likely to drive 20 miles a day if they’re in the midst of sprawl. In all, 46.8 percent of teens drive 20 miles per day in sprawl, while only 21.7 percent of teens in compact urban settings drive that distance.
With more miles on the road comes a greater risk of injury or death. Approximately 43,000 Americans per year are killed in auto accidents. For every teen-ager who dies as the result of an auto accident, 400 others sustain serious injuries, and 18 are hospitalized.
“For every age group from 3 to 33 in Atlanta, the leading cause of death is traffic crashes,” says Dr. Richard Jackson of the UCLA School of Public Health. Jackson says some cities offer lessons in how to save lives. If the US had the same traffic fatality rate as Portland, Oregon, the number of deaths nationwide would be reduced by 15,000, he says. “If the whole country had the New York City rate, there would be 24,000 fewer deaths per year.”
See also: Ride transit, lose weight
