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Status Report, Vol. 49, No. 1 | February 20, 2014 Subscribe

Safer vehicles benefit all occupants

Both older and younger passenger vehicle occupants are benefiting from efforts to improve protection in crashes, a National Highway Traffic Safety Administration (NHTSA) study confirms.

Researchers estimated the effectiveness of various occupant protection technologies in preventing deaths of drivers and right front-seat passengers ages 13-49 and 70-96 in 1960-2011 model passenger vehicles in crashes during 1975-2010.

Safety belts have historically been somewhat less effective for older occupants than younger ones, the authors note. For example, some earlier belt designs were more likely to cause rib and other injuries in older occupants than younger adults in crashes. In older model cars, two-point automatic belts were less effective for people 70-96 years old than for occupants ages 13-49.

The latest generation of belts with pretensioners and load limiters in vehicles with dual airbags may be just as effective for adults of all ages, as well as for both men and women, the study found. Belt pretensioners tighten up slack when triggered by vehicle sensors and retract the belt almost instantly in a crash. Load limiters manage the force that belts apply to occupants' chests in a crash by allowing some of the webbing to spool out when the forces exceed levels that can cause injuries.

Prior IIHS research has indicated in certain severe crashes, including small overlap front crashes, shoulder belts with load limiters may spool out too much, allowing occupants to move enough to strike hard surfaces inside the vehicle (see "Crash injuries may be prevented or caused by tension in the belt," Oct. 13, 2007). Still, NHTSA's study suggests that these features are evening out protection for all occupants and supports a new IIHS analysis suggesting that safer vehicles are helping to reduce older drivers' risk of dying in a crash.

Front airbags are about equally effective across all age groups for both drivers and right front passengers, NHTSA's study indicates. Side airbags with head and torso protection provide a much bigger benefit for older occupants than younger ones. Researchers estimated that side airbags lower fatalities in nearside impacts by 45 percent for people 70 and older in front seats, compared with an estimated 30 percent reduction for front-seat occupants ages 13-49.

Front airbags have been required since the 1999 model year. Side airbags aren't mandated, but the majority of 2008 and later models have them as standard to meet federal side protection requirements and to earn a good rating in the IIHS side crash test.

NHTSA also calculated the odds of dying in a crash by driver age and gender. Starting at about age 21, the risk of dying in a crash rises about 3 percent with each birthday. A 75-year-old man is, on average, 5 times as likely to die as a 21-year-old man in a similar crash. A 75-year-old woman is 4 times as likely to die in a crash as a 21-year-old woman in a similar crash.

Women have about a 25 percent higher risk of death than male drivers of the same age in the same type of crash, up to about age 35. Then men's advantage starts to slip, and by the time they reach age 70, both men and women have similar risk.

Women in particular have benefited from safety improvements, especially airbags and belts with pretensioners and load limiters. The estimated increase in fatality risk for females relative to males of the same age fell sharply beginning with mid-1990 models and had dropped by half in 2005-11 models.

Fatal injuries to the thorax, abdomen and neck increased the most with age; fatal head injuries increased the least. Females were much more likely than males of the same age in similar crashes to sustain fatal neck and abdominal injuries and moderately more likely to have head or chest injuries.

NHTSA has proposed adding a so-called silver car rating to the New Car Assessment Program to help older drivers choose potentially safer vehicles. Since the agency's new analysis indicates that both older and younger occupants are benefiting from safer vehicles, a silver car rating might not be any more beneficial than NHTSA's 5-star safety ratings program. Although it is possible that some crash protection designs might protect older and more fragile people better than other designs, such features help younger drivers, too.

To further explore this issue, IIHS researchers updated a prior analysis of driver death rates (see "Dying in a crash," June 9, 2011). IIHS calculated standardized death rates per vehicle registration by make and model for 2006-08 vehicles during calendar years 2006-09 for a hypothetical population 65 and older and a hypothetical younger population. Researchers adjusted for other factors that affect crash risk, including calendar year, vehicle age, driver gender and the vehicle density in the areas where each vehicle is typically registered. These are known to affect the likelihood of a crash and the likelihood that it will be fatal. Differences in these variables can affect driver death rates in ways that don't reflect the vehicle's inherent safety.

The estimated driver death rates for every model were higher for the hypothetical group of older drivers than the younger drivers. However, the rank order of vehicles by driver death rates was highly correlated for both groups, suggesting that the safest vehicles apply to younger and older drivers alike.

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Older drivers' crash rates continue to drop

Today's older drivers are not only less likely to be involved in crashes than prior generations, they are less likely to be killed or seriously injured if they do crash, a new Institute study shows.

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