LOS ANGELES—A suspicious device found on a bus has forced authorities to close several lanes of a downtown Los Angeles freeway as the bomb squad investigates.

LAPD Sgt. Herb Chang said the bus driver discovered the device on the empty bus late Sunday as he was about to begin his shift.

Because the bus was parked on a street that leads to State Route 110, the California Highway Patrol closed several southbound freeway lanes as the bomb squad checks out the device.

The shutdown caused traffic around downtown to back up.