A 42-year-old jogger was struck by a school bus and critically injured Tuesday in the North Potomac/Rockville area of Montgomery County, the police said.

They said no children were in the bus when the incident occurred about 2:30 p.m. at Shady Grove and Darnestown Roads.

The pedestrian, Jason A. Estabrook, of Point of Rocks, had been jogging northbound on the sidewalk, alongside the southbound lanes of Shady Grove Road. He was struck by the bus after he entered the intersection of Shady Grove and Darnestown, the police said.

They said the bus had been going south on Darnestown, in the lane next to the curb.

Police said Estabrook remained in critical condition Tuesday night at Suburban Hospital.

The incident is still being investigated.

The intersection of the two heavily traveled roads is about one mile west of Interstate 270. It is close to several major county institutions: the Montgomery campus of Johns Hopkins University, Shady Grove Adventist Hospital and the Center for Advanced Research in Biotechnology.

This report has been udpated.