The Insurance Institute for Highway Safety is an independent, nonprofit research and communications organization dedicated to reducing the losses - deaths, injuries, and property damage - from crashes on the nation's highways. The Institute is wholly supported by automobile insurers. The Institute is headquartered in Arlington, Virginia, and has a vehicle research center located in Ruckersville, Virginia (about 20 miles north of Charlottesville). The Institute's website is www.highwaysafety.org.
During the past 50 years, motor vehicle occupant death rates per mile driven have been dropping. However, passenger vehicle occupant deaths still are high; approximately 42,000 deaths have occurred per year for the past 2 years. Reducing the losses from motor vehicle crashes requires a balanced approach with programs aimed at changing driver and other road user behavior, improving vehicle designs, and modifying the road environment. Countermeasures should be based on research demonstrating their effectiveness.
The Institute's research agenda addresses the full range of highway safety problems with programs aimed at, for example, alcohol-impaired driving, young drivers, safety belt use, motorcycle helmet use, child restraints, and road and traffic engineering. This paper focuses on vehicle design, restraint systems, vehicle crash testing, and automated enforcement of traffic laws.
To protect occupants in serious crashes, a good structural design should have a strong occupant compartment (safety cage) and front and rear ends designed to buckle and bend to absorb crash forces. It is important for these crush zones to keep damage away from the safety cage because, once the cage begins to collapse, the likelihood of injury increases rapidly. If effectively designed, a crush zone lowers both the likelihood of damage to the occupant compartment and the crash forces inside it.
Not all vehicles are equally well designed. Some have crush zones that are too stiff and/or too short and safety cages that are not strong enough. These can contribute to the collapse of the occupant compartment in serious crashes.
The laws of physics dictate that, all else being equal, larger and heavier vehicles are safer for their occupants than smaller and lighter ones. In relation to their numbers on the road, small cars have many more occupant deaths each year than large cars (Exhibit 1).
Exhibit 1. Self-protection: occupant deaths per million registered vehicles; deaths in 1997–99 model cars, SUVs, and pickups during 2000–01 (available in full paper).
Size and weight are closely related. Large vehicles typically are heavy, and small ones are light. But these two characteristics do not influence crashworthiness in the same way. Vehicle size can protect occupants in both single- and two-vehicle collisions because larger vehicles usually have longer crush zones, which help prevent damage to the safety cage and lower the crash forces inside it.
Vehicle weight protects occupants principally in two-vehicle crashes. In a head-on crash, for example, the heavier vehicle drives the lighter one backwards, decreasing forces inside the heavy vehicle and increasing forces in the lighter one.