The frontage road near the Rillito Post Office is still closed after a tractor-trailer rig overturned.

The single-vehicle crash happened at about 7:20 a.m., said Capt. Adam Goldberg, spokesman for the Northwest Fire District. The driver was taken by ambulance to the University of Arizona Medical Center with minor injuries.

The truck was hauling dry lye, but none of it spilled onto the roadway, Goldberg said.

The east-bound lane of the west-side Interstate 10 frontage road south of Tangerine Road is expected to be closed until about 9:30 a.m. while crews tow away the truck, he said.

Officers from the Marana Police Department are investigating the crash, Goldberg said.