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Due to variables in data collection, testing, and human factors, consumer information on vehicle crashworthiness (the vehicle's ability to protect its occupants in a crash) is still in the development stage. Vehicle crash injury and fatality data collected for more than 30 years has enhanced consumer understanding of injury mechanisms and human tolerance in various types of impacts. Crash tests provide information to improve vehicle safety performance standards and to guide design improvements that increase a vehicle's crashworthiness. The size and weight of a vehicle are major factors influencing injuries and fatalities. More data have been collected on frontal crashes than on any other type, and this research has provided some conclusions about vehicle design features that may reduce the risk of injury. Side-impact crashes have also been researched extensively. Data from rollover crashes has not produced definite recommendations for reducing injuries. Research on rear-impact injury prevention is also ongoing.

The information summarized here was published under the chapter title "Current Understanding of Motor Vehicle Crash Avoidance and Crashworthiness" in Special Report 248 (National Academy Press, copyright 1996) from the Committee for Study of Consumer Automotive Safety Information of the Transportation Research Board. The report's title is "Shopping for Safety: Providing Consumer Automotive Safety Information."

ENGINEERING DATA

Several agencies are involved in gathering engineering data on vehicle crashworthiness. The National Highway Traffic Safety Administration's (NHTSA's) New Car Assessment Program (NCAP) gives consumers crashworthiness information from full-frontal crash tests conducted at 35 mph. NHTSA has also measured side-impact crashes in which the object striking the test vehicle was traveling at 33.5 mph. The stability measures that NHTSA proposed as "significant predictors" of vehicle rollover crashes have been challenged by the automobile industry--which places more importance on environmental and driver influences in these crashes.

The Insurance Institute for Highway Safety (IIHS) has begun testing frontal offset (off-center) crashes; however, there is no federal safety standard for this type of crash.

Consumers Union, which publishes Consumer Reports, has developed a test to measure stability, handling, and rollover tendency by driving a vehicle at increasing speeds until it can no longer be controlled.

BIOMECHANICS RESEARCH

To establish thresholds of human tolerance, biomechanical engineers study how parts of the body react to various types of impact and what magnitude of impact causes serious injury. This data is used to measure crashworthiness; however, people should remember that variations in such factors as age and sex will produce variations in impact tolerance among individuals. Dummies developed for crash testing are based on a 5-foot-8-inch, 180-pound male.

CRASH DATA

Vehicle crash data has been collected from a variety of sources. NHTSA has produced the main traffic accident databases, including the Fatal Accident Report System (FARS), which has tallied fatal traffic crashes every year since 1975. Since 1979, the National Accident Sampling System (NASS) has provided estimates of crashes by type from police accident reports and detailed information related to research on crashworthiness of passenger cars and light trucks. Most states store police accident reports in computerized databases, although reporting criteria and information detail vary among states. The Highway Loss Data Institute (HLDI), associated with IIHS, collects insurance claim information and summarizes injury,

DATA ISSUES

Crash data has several limitations.

1. Human error and environmental factors affect crash statistics.
2. New car models require a period of years for study and, therefore, specific crash data is not available for cars newly released to the market.
3. Crash databases are affected by variables such as reliability, differences in reporting criteria, differences in reporting jurisdictions, and areas of interest.

Although crash testing provides a controlled setting to eliminate non-vehicle variables, reliability is also a concern. Test situations consider only a few of the possible "real-world" factors--such as speed, vehicle size, vehicle position, and driver characteristics--involved in a crash. To improve crash test predictions, results could be compared with actual crash data involving similar vehicles. Some evidence that suggests this approach might improve crash predictions for new cars, but they should include vehicle size and weight measurements in crash studies if the research is to improve predictions.

CURRENT STATE OF KNOWLEDGE FROM AVAILABLE DATA

Crash Avoidance

Although a driver's ability to avoid a crash is affected by vehicle design elements such as rollover tendency, steering, and braking performance, the "characteristics and behavior of the driver" must be considered.

Avoidance of rollover crashes has been a research priority. By the late 1980s, evidence that sport utility vehicles had a higher proportion of rollover crashes caused NHTSA to propose a standard of vehicle stability. Because of different opinions about whether the rollover predictions are accurate, a rollover standard has not yet been established. Research has focused on antilock brakes, brake lighting, tire and brake performance, and vehicle "conspicuity." Such new technologies as enhanced night vision and collision avoidance systems, being developed with the Intelligent Transportation Systems (ITS) program, could help drivers perceive and more quickly react to conditions that might cause a rollover.

Crashworthiness

Design factors such as size, weight, and integrity play a role in a vehicle's ability to protect crash-involved occupants from injury. Crash data indicate which vehicle-related factors affect crashes and the types of crashes that cause the most deaths and injuries. Human factors such as age, belt use, and location within the vehicle also affect crash injury likelihood.

Vehicle Size and Weight

Large, heavy cars generally offer more protection to their occupants, with fatalities in lighter vehicles averaging two to three times the fatalities in heavier vehicles. Because of their additional size, larger vehicles allow more "crush space" to absorb impact. Vehicle size is not a major consideration in single-vehicle crashes as a whole, but it is "the key factor" in rollovers. A disadvantage of larger vehicles, however, is their increased fuel consumption. Although consumers should be provided a vehicle's size and weight information to evaluate its crashworthiness, this is only one factor to consider.

Crash Types

Fifty-one percent of vehicle crashes that result in highway deaths and injuries involve frontal crashes. The next-most-common types are side-impact (25 percent), rollover (15 percent), and rear-impact (9 percent). The authors pointed out, "Vehicle involvement in frontal-, side-, and rear-impact crashes occurs primarily in multiple- vehicle collisions, whereas vehicle involvement in rollovers is more common in single-vehicle crashes."

Rollover crashes produce the largest percentage of fatalities (one-third of all fatalities), with side-impacts producing a similar percentage. Frontal crashes produce the largest percentage of injuries.

Light trucks (sport utilities, pickups, and vans) have twice the likelihood of involvement in rollover crashes that include fatalities and injuries as passenger cars, but they are less likely to be involved in side-impacts.

Frontal Crashes

The top research priority has been frontal crashworthiness. Expressing concern about the barrier crash-test method used in crashworthiness research, the authors commented:

Moreover, although tests focus on full frontal crashes, usually frontal crashes are offset. Offset crashes demand more of the vehicle's structural integrity, because more of the impact must be absorbed by a smaller section of the vehicle. Injuries to the lower leg are a severe risk in offset crashes, even when vehicle occupants are belted and the vehicle has air bags. Federal performance standards for frontal offset crashes have not been established in the U.S.

Although test dummies are being customized for lower-extremity injury studies, factors such as head injury, chest load, and femur load vary widely and affect test reliability. There has not been an updated study of test variables to see if they have decreased. Nevertheless, passenger car manufacturers are becoming more consistent in safety features.

Side-Impact Crashes

High fatality rates in side-impact crashes are attributed to serious injuries to chest, abdomen, and pelvis and to the involvement of more older drivers than in other crash types. The federal standard proposed by NHTSA in 1988 for levels of side impact protection has been revised, and research continues into the effectiveness of incorporating the protection of stronger side doors, interior door padding, and side-impact air bags.

Because of high fatalities in side-impact crashes, a side-impact dummy was developed to measure injury probability. The most effective way to prevent side-impact injuries must still be determined, including the best type of padding and the optimum side-impact air bag pressure. Thus, side-impact consumer guidelines are premature for current vehicle models.

Rollover Crashes

Fatality rates in rollover crashes are highest in utility vehicles and pickup trucks. Most severe and fatal injuries occur to the head and neck when a person is thrown from the vehicle. Being ejected causes nearly two-thirds of rollover fatalities.

Unbelted persons who remain in the vehicle also suffer severely. Those wearing seatbelts suffer the fewest of the above types of injuries and only 13 percent of rollover fatalities, but they are susceptible to injuries from roof crushing. The authors pointed out, "Because of the complexity of possible impacts and the range of occupant positions at the time of the crash, biomechanical solutions for the retained occupant are beyond the state of the art."

Crashworthiness research conducted by NHTSA focuses on door locks and latches, shatterproof side windows, and increased roof strength, in addition to testing devices to enhance researchers' understanding of what causes different vehicles to roll. No protection tolerance levels have been established for vehicle occupants in rollovers, so consumer information is premature in this category also.

Rear-Impact Crashes