This is why you should use 4 straps or chains per car.

Car hauler dumps fuel and cars, closes I-70 for 9 hours | | Zanesville Times Recorder
NEW CONCORD -- A nearly nine-hour closure of Interstate 70's westbound lanes on Tuesday was caused by a the rollover of a car hauler that dumped fuel and cars.

The accident happened around 8 a.m. and closed lanes until just before 5 p.m.

Lt. Mike Forshey, of the Ohio Highway Patrol Zanesville post, said Ronald H. Young Jr., 41, of East Greenville, Pa., was traveling west when he looked down at his GPS unit, and the hauler carrying nine vehicles slid into the guardrail, carrying the cab of the car hauler with it.

Three cars were ejected and rolled into the field, Forshey said, while the cab containing Young rolled over and landed on its roof.

The driver also was not wearing his seat belt... so he did have to go to the hospital for injuries. Moral of the story-- strap yourself AND your cars. You just never know.