THE BURNED OVER DISTRICT

If you have one of the many models of the 14 automakers that used Takata airbags (Check here) with the ammonium nitrate trigger that hasn't been recalled yet, you may want to see if the dealer will fix it anyway.

More than a decade after the first confirmed rupture of a Takata airbag in Alabama, and despite a vast recall spanning 14 automakers, a stark reality remains: Tens of millions of people drive vehicles that may pose a lethal danger but have not been repaired or, as in Mr. Knight’s case, have not even been recalled.

Since 2000, Takata has sold as many as 54 million metal “inflaters” in the United States containing ammonium nitrate, an explosive compound that regulators believe is at the center of the problem, according to an estimate by Valient Market Research and provided to The New York Times. About 28 million inflaters in 24 million vehicles have been recalled. And of the 28 million recalled inflaters, only about 30 percent have been repaired. The rest of the inflaters, about 26 million, have not been recalled.

The National Highway Traffic Safety Administration has stepped up its scrutiny of the problem, after a series of missteps over nearly a decade, but has stopped short of an immediate recall of all Takata airbags containing the compound. The agency does not have the authority to order people to stop driving the cars and has not advised people to avoid driving them.

Gordon Trowbridge, a spokesman for the safety agency, said that not knowing the exact cause of the ruptures prevented broader recalls.

“It is unknown why some inflaters perform better than others,” he said. “It is unknown why the same inflater, with the same propellant formulation, performs better in some vehicles than in other vehicles.”

Still, he added, “If N.H.T.S.A. believes a vehicle presents an unreasonable risk to safety, the agency would seek a recall.”

Car manufacturers, at the same time, have been reluctant to sound alarms. They would face huge costs if they needed to provide loaner cars for millions of owners. Of the 14 manufacturers affected by the Takata recalls, not one has offered a blanket policy of supplying loaners.

Regulators have no authority to order automakers to make loaner cars available, but Mr. Trowbridge said his agency had encouraged them to consider doing so and had encouraged car owners to ask for loaners.

Given the size of the recall, Takata was the largest manufacturer of airbags, many automakers are dragging their heels because of the cost. Replacements parts have also been a bottleneck to getting it done.