ARLINGTON, Va. — Side airbags that include head protection are reducing deaths by about 45 percent among drivers of passenger cars struck on the near (driver) side. Side airbags that protect the chest and abdomen, but not the head, also are reducing deaths, but they're less effective (about 10 percent). These are the major findings of an Insurance Institute for Highway Safety study of the real-world effectiveness of side airbags. It's the first such study to estimate the effectiveness of this type of occupant protection.
Each year more than 9,000 passenger vehicle occupants die in side impacts. Head injuries are a leading cause. The new research findings mean the toll should be reduced in the future.
"The need for head protection in side impacts has been obvious for some time," says Institute president Brian O'Neill. "Before head-protecting airbags were available there was virtually nothing to prevent people's heads from being struck by intruding vehicles or rigid objects like trees and poles in serious side impact crashes. Now we know side airbags can change this and do a good job of protecting heads."
When occupants' heads are in the window areas of vehicles they're especially vulnerable to being struck by intruding vehicles or objects. O'Neill points out that "the increasing number of high-riding vehicles on the road these days increases this risk, making it more likely that the front end of a striking vehicle in a side impact will hit the heads of occupants in the struck vehicle. This is why side airbags with head protection are so important."
Side airbags that protect the torso only don't represent as fundamental a safety improvement. They're an alternative way to protect the chest and abdomen in a side impact, but not the only way. Padding the vehicle interior also can protect occupants' torsos.
Range of side airbag designs
Since the mid-1990s when Volvo introduced side airbags and BMW and others added head protection, more auto manufacturers have followed suit. By the 2003 model year, 40 percent of all passenger vehicle models offered head-protecting side airbags (24 percent standard equipment, 16 percent optional equipment; see attachment for list of 2004 model passenger vehicles equipped with side airbags).
Some passenger vehicles are equipped with combination torso/head side airbags. Other vehicles have two separate side airbags, one for the torso and another for the head. Most of the torso-only and combination torso/head designs inflate from vehicle seats, although some inflate from the door. Side airbags designed exclusively to protect the head — so-called curtains or tubular structures — inflate down from a vehicle's roof area.
Crash test results
Institute crash tests conducted since 1997 consistently have demonstrated the potential of head-protecting side airbag designs. These have produced much lower head injury measures on dummies in side-into-pole tests, for example, and in tests in which pickups hit the sides of lower-riding cars. In more recent tests in which a movable barrier representing the front end of an SUV or pickup struck the sides of small SUVs, the three best performers had head-protecting side airbags. In contrast, none of the seven small SUVs with the worst performances had such airbags.
Effectiveness in real-world crashes
To estimate side airbag effectiveness in on-the-road crashes, Institute researchers used data from the federal Fatality Analysis Reporting System and General Estimates System to compute the relative risk of dying for drivers of 1997-2002 car models with and without side airbags when their vehicles were struck on the left (driver) side. Besides computing the overall effectiveness estimates — 45 percent fatality risk reduction for drivers of cars with head-protecting side airbags, 11 percent reduction with torso-only side airbags — the researchers broke down the findings into more specific results.
Researchers found that side airbags with head protection reduce the risk of death for both male and female drivers over a wide span of ages. Significant protective effects were found for drivers of both large and small cars.
The effectiveness of side airbags with head protection is significant in two-vehicle collisions (53 percent risk reduction). The highest estimated effectiveness (74 percent risk reduction) is in two-vehicle crashes when a car with head-protecting side airbags is struck by another car or a minivan. Mortality reductions also were substantial when the striking vehicles were pickups or SUVs, suggesting that head-protecting side airbags are addressing some of the problems of incompatibility when passenger cars are struck in the side by vehicles with higher ride heights.