Hundreds of crashes involving defective cars are going unreported each year because under U.S. safety rules automakers aren’t required to report suspicious accidents for models more than 10 years old.

That’s worrisome, safety advocates say, because the average age of cars on U.S. roads is 11.4 years, and almost half of vehicles aren’t covered under existing regulations. As a result, many incidents don’t make it into a government early-warning database designed to catch patterns of defects that regulators can use to determine if a recall is necessary. In effect, the rules haven’t kept pace with the reality on the nation’s roads.

Legislation introduced in February by Representative Jan Schakowsky, an Illinois Democrat, would eliminate the 10-year limit as part of a broader effort to make safety data more useful to the public. That legislation is still being reviewed in committee.

“The law is absolutely out of date because companies have made it out of date by ignoring defects for so long in some of these cases,” said Joan Claybrook, a Washington-based consumer advocate who led the National Highway Traffic Safety Administration in the 1970s. “It ought to be open-ended.”

A collision involving Dianna Moulton, a 69-year-old grandmother from Dearborn, Michigan, shows how cases involving older cars fall through regulatory cracks. While Christmas shopping last year, Moulton drove into a parking lot lamppost. The accident left only a crack in the bumper of her 2002 Honda CR-V. But the air bag went off, exploding with such force she was left with a broken eye socket and other facial fractures.

Exploding Air Bags

The accident came to light only because Moulton sued Honda Motor Co. for compensation. Hers is one of at least seven cases filed in the past six months claiming air bags made by parts maker Takata Corp. explode with too much force. Moulton’s and one other case involved vehicles too old to be included in the early-warning database.

“It’s clear from the Takata air-bag debacle that the early warning system doesn’t work when it’s confined to a time frame,” said Kevin Dean, an attorney at Motley Rice in Mount Pleasant, South Carolina, who’s handling Moulton’s case.

Chris Martin, a Honda spokesman, said in an e-mailed statement that the company hasn’t confirmed any crash-related injuries were caused by an air bag deploying with excessive force; Honda is investigating the issue. Asked if the early- warning database should include vehicles older than 10 years, Martin said Honda will comply with “applicable federal rules now or in effect in the future.”