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Status Report, Vol. 39, No. 7 | August 1, 2004 Subscribe

Evidence mounts that reducing force of airbag inflation lowers risk

A federal court recently upheld a decision by the National Highway Traffic Safety Administration (NHTSA) that lets automakers reduce the inflation forces of frontal airbags. While the court was deliberating this decision, research evidence was mounting to indicate that depowered airbags, which have been installed in most passenger vehicles since the 1998 model year, have reduced deaths caused by airbags among children as well as adults, many of them women of short stature.

At the same time, no evidence has surfaced to indicate that reducing airbag inflation forces has compromised protection for bigger people in more severe crashes. It was this concern about the consequences of depowering airbags that motivated the legal challenge filed by Public Citizen and the Center for Auto Safety.

Airbag inflation deaths in 1989-2003 models

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"NHTSA's policy of allowing depowered airbags was right to begin with, and now the court is right to uphold the agency," says the Institute's senior vice president for research, Susan Ferguson.

From 1990 until April 2004, NHTSA reported 242 deaths attributed to airbags inflating in minor and moderate crashes. More than half of the deaths (147) were infants and children. But the deaths weren't distributed evenly during the 14-year span. Since the 1998 model year, when depowering began, deaths have plummeted. There have been only 12 airbag-related deaths in 1998 model vehicles, down from 30 deaths in 1997 models. Seven deaths have been attributed to inflating airbags in 1999 and later models.

For adults the reduction in deaths can be attributed largely to the redesign of airbags and, in some part, to education encouraging shorter drivers to sit farther away from their steering wheels. NHTSA recommends that drivers choose positions at least 10 inches from the wheel (see Status Report special issue: airbags, Nov. 29, 1997). Increased belt use also has been a factor.

Keep children away from airbags

NHTSA conducts ongoing investigations of crashes in which airbag-related deaths are believed to have occurred. Data collected as part of these investigations show a decline in the rate of children who have been fatally injured by passenger airbags. The peak was 83 deaths per 100 million vehicle registration years during 1995-96. This rate declined to 6 deaths per 100 million during 2002-03. The reduction occurred even as the number of vehicles equipped with passenger airbags continued to rise.

Much of the fatality reduction among children was due to extensive education to ensure that kids travel in the back seats of vehicles, away from frontal airbags. Less forceful airbag designs also contributed to the decline in deaths among children. Partners for Child Passenger Safety examined frontal crash injuries to children who were sitting in front passenger seats, finding the serious injury rate about 40 percent lower in 1998 and newer model vehicles compared with pre-1998 models.

Adults are benefitting, too

"Reducing airbag inflation force was the right decision for adults as well as children," Ferguson says. "Recent studies indicate that the airbags in newer vehicles provide as much protection in high-speed crashes but aren't as risky to out-of-position occupants, compared with the older airbags that inflate with more power."

Benefits of depowering

The findings of a number of studies were discussed at a recent meeting of the Blue Ribbon Panel for Evaluation of Advanced Airbags, a group of researchers and others gathering data on the newer airbag designs and evaluating them. Among the studies:

  • Data from the University of Miami's William Lehman Injury Prevention Center show lower fatality rates among patients who had been driving 1998 and newer model vehicles than pre-1998 models. The decline in airbag-related deaths among drivers in low-speed crashes was dramatic. Nine drivers of pre-1998 models died in crashes at speeds slower than 20 mph. In contrast there were no airbag-related deaths among drivers of 1998 and newer models in crashes at less than 25 mph.
  • Data from NHTSA's special investigations of drivers killed by airbags show a drop from a peak rate of 80 per 100 million vehicle registration years during 1990-91 to 5 during 2002-03.
  • A study comparing injury frequencies and severities in frontal crashes, using data from the National Automotive Sampling System/Crashworthiness Data System, indicates that drivers of 1998 and newer models were less likely to sustain moderate or severe injures than people driving vehicles with older airbags. Injury reductions occurred among both men and women in crashes at all speeds.
  • The University of Michigan Transportation Research Institute found that frontal crash protection for the heads, faces, necks, chests and abdomens (body regions airbags are designed to protect) of drivers in Michigan was at least as good in 1998 and newer models as in older vehicles. This study found very few cases of drivers or passengers sustaining severe injuries because their airbags didn't provide enough protection.
  • Last March the Institute compared driver fatality rates in 1998-99 model vehicles versus 1997s. The focus was on vehicles that didn't undergo significant structural changes during the study's three model years to better isolate the effects of the newer airbag designs. For all passenger vehicles except pickup trucks, driver fatality risk in frontal crashes was 11 percent lower in the 1998-99 models than in the 1997s. Fatality risk was higher among drivers of pickup trucks. Yet even with the pickups factored in, the overall risk of driver death was 6 percent lower in the passenger vehicles equipped with less powerful airbags (see "Depowered airbags cut the fatality risk for drivers of most vehicles," March 6, 2004).

"Taken together, these and other studies indicate a small but measurable increase in the effectiveness of the newer airbag designs compared with the older airbags that inflated with more force. Just as important, we haven't seen the large increase in deaths in high-speed crashes that some people were predicting," Ferguson says.

Road to depowered airbags

Automakers were able to make airbag design changes to reduce inflation forces because of modifications NHTSA made in frontal crash test requirements. A 1997 decision gave automakers an option of running less demanding 30 mph sled tests instead of the full front-into-barrier crash tests with unbelted dummies that had been required. This option was a stopgap until NHTSA had time to modify the occupant crash protection standard.

In 2000 the agency announced changes to the frontal crash test standard that went into effect in 2003. The modified rule reinstated full-front barrier tests with unbelted dummies but lowered the test speed from 30 to 25 mph. This led to the lawsuit challenging the test speed. The U.S. Court of Appeals for the District of Columbia decided the case in NHTSA's favor last month.

SIDEBAR
Court upholds 25 mph test speed

A federal appeals court sides with NHTSA over its decision to conduct crash tests with unbelted dummies at 25 mph instead of 30 mph.

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