NASHVILLE (AP) — The Tennessee Highway Patrol will conduct "no refusal" DUI enforcement in 16 counties over the Fourth of July weekend.

The practice allows troopers to get search warrants for blood samples in cases involving suspected impaired drivers.

Stepped-up traffic enforcement begins statewide at 6 p.m. Wednesday and lasts through midnight Sunday.

The Department of Safety and Homeland Security said 21 people were killed in 17 traffic crashes over the Independence Day holiday weekend in 2012, at a rate of about one death every six hours. Half of the crashes involved alcohol and nearly 40 percent of those killed weren't wearing seat belts.

AAA motor club estimates about 724,000 people will travel at least 50 miles from home over the holiday period — 84 percent of them by car.