WHEN regulators sleep and auto companies place profits over safety, safety defects pile up. A record number of vehicles — more than 50 million — have been recalled this year, a result of congressional hearings and Justice Department prosecutions, which exposed a mass of deadly defects that the auto industry had concealed.

From the Ford Explorer rollovers in the 1990s and Toyotas’ issue with unintended acceleration in the 2000s to the recent fatal consequences of defective General Motors ignition switches and Takata airbags, the auto companies hid defects to avoid recalls and save money. These and other major defects were first exposed by safety advocates who petitioned the government and by reporters in the tradition of Bob Irvin of The Detroit News, who wrote over 35 articles on Chevrolet engine mounts until General Motors agreed to recall 6.7 million vehicles in 1971.

These campaigners did the job the regulator should have done. Congress gave the Department of Transportation authority to regulate the auto industry through the National Highway Traffic Safety Administration — including subpoena authority to find defects. But it used this authority so infrequently after the ’70s that its acting administrator, David J. Friedman, told Congress this year that he didn’t even know it had the power. The N.H.T.S.A. also failed to require companies to disclose death-claim records in civil lawsuits over the Toyota accelerations, G.M. ignition switches and Takata airbags.

In order to prevent the risk of death or serious injury, Congress empowered the agency to oblige auto companies to use alternate suppliers and independent repair shops to manufacture parts and make repairs to expedite a recall fix. Yet the N.H.T.S.A. has never used this authority — even though it took General Motors from February to October to get enough parts to dealers to repair all the recalled ignition switches.