The pickup truck burst into flames, and the driver was declared dead at the scene on Interstate 10 in Casa Grande, about 50 miles south of Phoenix. Authorities couldn't immediately say if he died on impact or in the ensuing fire.
Arizona Department of Public Safety officials identified the driver as Francis Wilkens Gibson Jr., 78, of Casa Grande. They said the cause of the crash remained under investigation and "nothing has been ruled out at this point."
DPS Capt. Brian Preston said investigators will be working to determine whether drugs or alcohol were a factor.
Nine of the 15 passengers on the bus were injured, but none of the injuries was considered life-threatening, DPS said. Two passengers were flown to Casa Grande Regional Medical Hospital, and the other seven were taken to the same facility by ground ambulance.
The bus driver was conscious and walking around when authorities arrived, Preston said.
"Generally when you have a vehicle going the wrong way on an interstate, you'd think it would be much worse than this," he said.
The charter bus was owned by TBC Connexion and was travelling from Mexico to Phoenix, according to authorities. The names, ages and hometowns of the bus driver and passengers weren't immediately released.
Calls to TBC Conexion's offices in Phoenix and Tucson weren't returned Tuesday evening.
DPS officials said that about two minutes before the 2:15 p.m. crash, they received two 911 calls about a driver on I-10 — the main route from Phoenix to Tucson — travelling east in the westbound lanes.
"We were responding when the accident occurred," said DPS spokesman Bart Graves.
The fiery crash closed the westbound lanes of the freeway near Interstate 8 for hours, backing up traffic for miles until one lane was reopened Tuesday evening. The bus still sat on the side of the freeway, its front end crumpled from the impact, and several windows blown out.
Graves said an 18-wheeler jackknifed at the accident scene and hit the side of the bus, but the main damage was done by the pickup truck. The driver of the tractor-trailer wasn't injured.