An erratic driver on U.S. Route 202 struck a bus Wednesday afternoon, police said, but a witness said there could have been much more damage if not for another driver who intervened and forced the man to stop.

Russ Baer said he was driving from Bangor to Augusta when he noticed a person who was driving slowly, and often in the wrong lane. He said it got to the point that other drivers were getting off the road to avoid the driver. Then, he said, the driver sideswiped a commercial bus and drove off, and the crash tore off part of the bus and left debris in the road.

Baer said he was driving behind the man when he called the police. He said he was behind the car for about 10 or 15 minutes, and said the driver was in the wrong lane most of the time.

“It could have been pretty bad,” Baer said.

The driver eventually was forced to stop by another driver, Tyler Jepson.

Chief Deputy Jason Trundy, of Waldo County Sheriff’s Office, said Thursday the incident was still under investigation, though it appeared the driver, 67-year-old David Brandt, of Northport, was not inebriated but rather had experienced some kind of medical problem. He said it was too early to know if police would file charges, and that after Brandt was stopped, he was taken to Waldo County General Hospital in Belfast. Trundy confirmed that Brandt was reported to have hit the bus.

Baer said the driver had not been going fast until he hit the bus. After that, the driver crested a hill and Baer lost sight of him temporarily. When he saw the driver again, he was much farther away.

At one point, Baer said, Jepson’s car rushed past him and passed the erratic driver on the right, as that driver was in the wrong lane, and maneuvered in front of the driver to force him to stop. According to Baer and Trundy, Jepson then took away Brandt’s car keys so he could not start driving again.

“This kid somehow got him to stop,” Baer said.

Trundy said Brandt had been coming from Bangor, where he had had a medical appointment. He said there was some indication Brandt might have been involved in a car accident in a parking lot in Bangor as well.

Baer, who waited at the scene with other drivers until police arrived, said Brandt indicated he did not remember hitting the bus. Baer called Jepson a hero, because Brandt was frequently in the wrong lane and could have caused other accidents. He said if not for Jepson, it’s likely Brandt wouldn’t have stopped until he hit another vehicle.

“He saved some lives, I think,” Baer said.