Despite faulty ignition switches, millions of GM cars can stay on the road.
Senators Ed Markey and Richard Blumenthal had asked the Transportation Department to issue a warning, telling drivers to park the cars until the switches are replaced.
But the National Highway Traffic Safety Administration says such a warning is not necessary because General Motors has mitigated the problem.
The automaker says drivers should remove everything but the ignition key from their key rings.
GM is recalling more than two-million cars worldwide to replace ignition switches that suddenly can slip out of the run position and shut off the engine.