Road Management & Engineering Journal
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The United States is a highly urbanized society. In 1990, three-fourths of the population lived in metropolitan areas, according to the U.S. Census, and the majority of the nation's population growth during the next 25 years is predicted to be in metropolitan areas. Vehicle miles traveled also are increasing rapidly in urban areas. From 1980-95, total vehicle miles traveled rose 59 percent, but miles traveled in urban areas grew 74 percent.
1. How significant is the problem of urban crashes? Crashes that cause injuries and/or property damage occur at the highest rates in urban areas. Fatal crashes, however, are more likely to occur in rural areas. A 1989 Insurance Research Council study of a national sample of automobile crash injury claims found that 81 percent of the crashes occurred in urban areas. A January 1995 report by the Highway Loss Data Institute examined insurance injury claim frequencies for 1991-93 model vehicles and collision claim frequencies for 1992- 94 model vehicles garaged in 12 metropolitan areas of the United States. Injury claim frequencies were 29 percent higher in these urban areas than in the rest of the country, and collision claim frequencies were 34 percent higher. Pedestrian deaths and injuries are most prevalent in urban areas; 72 percent of pedestrian deaths occur in urban settings.
2. What are the most common types of urban crashes? A 1995 Institute study of more than 4,500 crashes in four urban areas found that 22 percent involved drivers who ran red lights or other traffic controls such as stop or yield signs. Eighteen percent occurred when a vehicle that was stopped or in the process of stopping was struck from the rear. The three other leading types of urban crashes include running off the road and striking an object (14 percent), swerving into another occupied lane (13 percent), and turning left and colliding with an oncoming vehicle (9 percent). These five crash types accounted for three-fourths of all urban crashes included in the Institute's study and 83 percent of crashes involving injuries.
3. Which crashes are most likely to cause injuries? In urban areas, motorists are most likely to be injured in head-on collisions and crashes involving red light running. Occupant injuries occurred in 45 percent of both head-on crashes and red light running crashes the Institute studied. Left-turn crashes produced the second highest number of occupant injuries. Forty-one percent of urban crashes associated with a vehicle turning left into oncoming traffic involved injuries. These crashes often involve a side impact. More than a third each of crashes typed as running a traffic control, rear-ending a stopped or stopping vehicle, and running off the road involved injury. In contrast, injuries occurred in only 16 percent of crashes involving lane change maneuvers.
4. Where and when do urban crashes occur? Crashes categorized as running a traffic control (a signal light or a sign) or turning left into oncoming traffic are most likely to occur at intersections. Left-turn-oncoming crashes are particularly associated with traffic signals. Rear-end collisions into stopped or stopping vehicles occur at roadway intersections and between intersections with equal frequency. Of the five major urban crash types, only run-off-the-road crashes are most likely to occur at night. Pedestrians in urban areas are more likely to be injured in crashes at intersections. An examination of fatal pedestrian crashes in four U.S. cities found 40 percent involving vehicles other than large trucks occurred at intersections, and 51 percent involving large trucks occurred at intersections.
5. Can vehicle design changes reduce urban crashes? Yes. One promising new crash avoidance feature expected to help reduce two-vehicle crashes is daytime running lights. Activated by the ignition switch, daytime running lights increase vehicle conspicuity during daylight hours, making it easier to detect approaching vehicles. Many manufacturers are beginning to make the lights standard on their vehicles. Another crash avoidance feature now standard on cars is high center-mounted stop lights a third brake light usually located in a car's rear window. By prominently alerting following drivers that the car in front is braking, the lights have helped reduce the incidence of rear-end collisions.
Good bumpers won't help drivers avoid crashes, but they can reduce repair costs associated with low-speed crashes, which occur frequently on urban streets and in parking lots. A 1991 Institute study of cars brought to 16 insurance drive-in claims centers in 4 metropolitan areas reveals that about 20 percent of all claims for auto damage involve parking lot collisions just the kinds of impacts in which strong bumpers could reduce or eliminate much of the damage. Yet bumpers are not nearly as damage-resistant as they should be because federal requirements for car bumpers are weak, and no requirements at all apply to the bumpers on pickups, passenger vans, and utility vehicles.
Head restraints are an important safety feature often overlooked in many cars. Head restraints can prevent "whiplash" injuries in relatively minor rear-end crashes, the kind of crashes that occur frequently on urban streets. Rear-end collisions account for 18 percent of all urban crashes, second only to crashes involving running a traffic control. Neck injuries, particularly whiplash, occur with significantly higher frequency in rear-end crashes than in other crash configurations. This is why it's so important for vehicle head restraints to be well-designed to adequately protect occupants. Head restraints should be high enough so they're directly behind and very close to the backs of people's heads the closer the better.
6. Can tougher law enforcement help? Common traffic infractions like speeding and red light running are associated with many urban crashes. Speed cameras and red light cameras can help police enforce traffic laws in dense urban areas where traffic pursuits and stops can be dangerous to officers and to other motorists and pedestrians. Speed cameras, used to enforce speed limit laws, have been used only on a limited basis by U.S. police, although they're used extensively worldwide, including in Canada, Australia, and throughout Europe. In addition, consistent police enforcement of safety belt use laws will result in fewer motor vehicle fatalities and injuries resulting from all crash types.
7. What countermeasures can officials implement? Identifying major urban crash types allows city officials to focus on specific ways to prevent future crashes. The most common crash type a driver running a traffic control might be reduced by lengthening signal clearance intervals, improving signal and sign visibility, increasing sight distances, and reducing vehicle speeds near intersections. Red light cameras, now used in the United States, also can play an important role. Research also shows that intersection crashes may be substantially reduced by installing modern roundabouts in place of signals and stop signs under appropriate conditions.
© 1999, The Insurance Institute for Highway Safety