The air bags that the government requires in cars are a "one size fits all" technology that cannot succeed in all circumstances, the National Highway Transportation Safety Administrator said Monday.
The administrator, Dr. Ricardo Martinez, a medical doctor, said the bags being manufactured under rules that were in effect until last Friday have been killing children because "the dose is too big."
Martinez testified at the beginning of a four-day hearing by the agency on air bags, which are credited with saving 1,810 lives and taking 71 others, including 38 children.
Last week the agency tried to reduce the risk to children, small adults and people who are unbelted and may not be reclining in their seats when the bag deploys, by allowing manufacturers to lower the force of the bags 20 percent to 35 percent. But some experts said that might mean saving some children and small adults and sacrificing some larger drivers and passengers, an uncommonly stark policy trade-off.
The testimony revealed many gaps in knowledge about air bags and driving habits, including how many people usually wear seat belts. States have reported to the agency that their surveys show that 68 percent wear belts, more than three times the level when air bags were first thought up.
Some experts think the real number is lower. The 68 percent figure is reported by the states, and some omit pickups and other non-auto vehicles, because those are not covered by those states' laws.
Among the people involved in fatal crashes, a much more carefully counted number, only about half were wearing belts.
The number of people wearing seat belts is crucial, because designers have to choose whether they are building the devices primarily for those with belts or those without. To meet federal test requirements, some air bags in use open at speeds of 200 mph. The reason they open so forcefully is that the test that the bags had to pass until last Friday was designed to protect unbelted dummies.
Some witnesses said the solution was to think of bags as a supplement to belts, not as a replacement. A vice president of Ford Motor Co., Helen Petraskas, said, "Our first objective has to be to protect the belted occupant, and then set ourselves the goal of doing no harm." The third goal, she said, is protecting someone who is not belted, but not at the cost of harm to people who are belted.
Dr. Donald Huelke of the University of Michigan Transportation Research Institute agreed that the bags should be designed for people who wear belts.
"In every state but one," Huelke said, "we have a law requiring use of the belt system. Here we have the federal government saying, "You also have to help out this guy who is breaking the law.' To me there's something paradoxical about that."
But the technology is probably easier to change than the culture, said Brian O'Neill, president of the Insurance Institute for Highway Safety. The problem, he said, is that the hardware change will take time.
O'Neill said air bags probably saved far more people than they killed. But, he said, "we could do a lot better if people buckled up." Of the 38 children, he said, nine infants died because they were in rear-facing seats that should have been in the back seat. Of the remaining 29, he added, 24 were not belted at all, and some of the remaining five were restrained only by the lap sections of their belts.