An off-duty Montgomery County police officer was trying to help motorists involved in two crashes on a slippery road Tuesday evening when a third car crashed into him, authorities said.

Officer Fabio Chung was treated at a hospital for his injuries and released after the incident at a ramp leading from Route 118 onto Interstate 270, the county police said. The southbound lanes of the highway were shut down for about two hours.

The crashes, and others that occurred in the same area, apparently resulted from oil that leaked onto the roadway from a disabled bus, state police said.

County police said they were notified about 5:15 p.m. of two crashes on the ramp from eastbound Route 118, Germantown Road, onto southbound lanes of the interstate. Cars had slid off the road as they headed down the ramp, police said.

Although off duty, Chung, who is assigned to patrol, went to help. At the scene, a third car slid off the road and struck him, county police said. His cruiser also was hit.

State police said a bus had become disabled by engine problems and was leaking oil. The oil was on the ramp and the interstate, and, according to state police, apparently resulted in other crashes in addition to the three cited by the county police.

Moisture on the road may have made conditions more difficult, police said.

No serious injuries were reported.