Phoenix, June 11 : Four people were killed and multiple others injured in a road accident in the US state of Arizona involving a commercial truck transporting milk and seven other vehicles, authorities said. The incident took place on a freeway in Phoenix at 10.09 p.m. on Wednesday night, Xinhua news agency quoted the Arizona Department of Public Safety as saying on Thursday. The commercial truck-tractor pulling a tanker trailer filled with milk failed to slow for traffic congestion in the area of 52nd and Van Buren Streets and collided with the other seven vehicles, the Department said. The truck's trailer separated and crossed over the concrete median wall into the westbound traffic lanes where it came to rest on its side within the high-occupancy vehicle lane. The truck ignited and was destroyed by the fire, according to the Department. Authorities said four people died as a result of injuries sustained during the collision and several patients were transported to local hospitals with serious to life-threatening injuries. An investigation of the crash is under way. Officials said they have ruled out the possibility of impairment. /IANS