Seven people traveling east on Interstate 10 in a minivan were killed Sunday morning when a westbound tractor-trailer crossed the median and crashed head-on into the vehicle, setting it on fire, according to the Arizona Department of Public Safety.
The driver of the tractor-trailer and his wife escaped after the vehicles collided near the Burnt Well Rest Area.
The tractor-trailer and van plunged down a 6-foot embankment and burst into flames, said Carrick Cook, a spokesman for the state DPS.
Charges will probably not be filed because investigators believe the driver has a medical condition, Cook said.
The 11a.m. crash near mile marker 87.1, about 50miles west of Phoenix, was one of six fatal accidents that killed 12 people over the weekend, Cook said.
That marked the second weekend in a row of a high number of traffic-accident fatalities.
"It's unusual," Cook said.
The semitruck driver and his wife were hospitalized with injuries.
Autopsies are scheduled for Wednesday for the seven victims, believed to be family members.
The youngest were probably teenagers, Cook said.
Identifying the victims is complicated by the violent nature of their deaths, Cook said.
Eastbound I-10 was closed for most of the day on Sunday. DPS officers were expected to reopen the freeway Sunday night.
Other fatalities on the state's highways over the weekend were reported in areas near Payson, Casa Grande, Tucson, Flagstaff and Yuma.