Safety sweep finds some big buses still unsafe, but national crackdown may be having an effect

A national crackdown on unsafe commercial bus companies may be having an effect.

Troubled by a series of fatal crashes, government inspectors focused on motor coaches during their annual blitz of roadside safety checks.

According to data released Wednesday, serious mechanical problems kept 7 percent of motor coaches or other large passenger vehicles off the road.

But that rate was the lowest in more than a decade of the "Roadcheck" safety sweep, which this year saw 73,000 inspections of trucks and big buses over three days in June across the U.S. and Canada.

While motor coaches are generally safe, several major accidents led U.S. transportation officials to worry that low-cost companies may be cutting corners.

Regulators began targeting certain carriers, shutting down those they believe are the most dangerous.