Among the problems discovered by inspectors were "four undercarriage frame cracks including at the drive axle, at the cross member for the motor mounts, and at the differential and over the right front steering axle, " according to a letter sent by Berwick to Federal Motor Carrier Safety Administration Administrator Anne Ferro.

WSJ: Mass. official: Buses pulled from road for safety

It also, though, has an electric motor that provides additional power to the rear wheels (through the same gearbox) and a second electric motor connected directly to the front axle.

ECONOMIST: Fast cars will go even faster with electric power