Muni is investigating a bizarre Jan. 20 accident in which one of its parked and empty trolley buses rolled down a hill and smashed into several parked cars in Daly City.

The operator of the bus said he had applied the emergency brake on the 60-foot-long vehicle before leaving it unattended on a downhill slope at Mission Street and San Jose Avenue, an area popularly called Top of the Hill, according to officials from the San Francisco Municipal Transportation Agency and Daly City police.

Around 3:30 p.m., the operator took his customary break at the end of his bus route, parking in a space designated for Muni buses, Daly City police Sgt. David Mackriss said.

During his break, the rogue bus suddenly rolled across a sidewalk and into a parking lot, crashing into three parked cars, SFMTA spokesman Paul Rose said.

Those cars were pushed into two more vehicles. There was just one person occupying one of the five damaged cars, Mackriss said.

“The person complained of pain to his arm,” said Mackriss, adding that the injury was minor.

Muni transit inspectors joined cops at the scene. It took “several hours to lift the bus off the concrete divider,” police said.

According to a witness, the wheels of the parked bus were appropriately turned toward the curb, Mackriss said. The operator told police he had applied the emergency brake on the bus and heard a loud pop just before the vehicle rolled downhill.

Muni is investigating the operator’s claims.

“We’re looking into exactly what happened,” Rose said.

The operator, whose identity was not released, has been placed on nondriving status pending the results of the investigation, Rose said.

maldax@sfexaminer.com