Malay Mail Online quoted Perak traffic police chief Supt Wan Jamil Wan Chik saying police would also check if the driver, who would be remanded today, was under the influence of drugs or alcohol.
Another possibility the authorities are looking at is mechanical failure.
The incident happened at about 2.45pm yesterday when the bus, coming out of a bend in the highway at high speed, rammed into 10 cars.
No one was reported hurt in the incident.
Footage of the crash, recorded with a static traffic camera, is being circulated online.
Traffic was already very heavy with thousands of commuters returning to Kuala Lumpur after the end of the Aidilfitri holiday week, with the accident causing further congestion between Alor Setar and Ipoh.
