An off-duty Bladensburg police officer was killed Saturday in a car crash in Anne Arundel County, county police said.

The officer was identified as Brian Johnson, who was a member of the Bladensburg department for nine years. Johnson also was a member of the volunteer fire department in Bladensburg, which is in Prince George’s County.

Johnson was driving a marked police cruiser and apparently was on his way to his home in Anne Arundel when the crash occurred about 9 a.m.

Anne Arundel police said the car was headed east on Route 100 near Catherine Avenue in the Pasadena area. Route 100 is a divided highway with a grassy median. The officer’s car “suddenly crossed the median” and struck a westbound vehicle, Anne Arundel police said.

Johnson was taken to the Baltimore Washington Medical Center, where he was pronounced dead, police said.

The operator of the other vehicle was treated at the scene.

Anne Arundel police said a preliminary investigation indicated that the officer may have suffered a medical emergency before the crash.

The matter was still being investigated, police said. No details about the possible emergency were available. Johnson was in his late 30s, according to public records.

In a statement, Bladensburg’s police chief, Charles Owens, called Johnson a cherished member of the department and a dedicated public servant who would be missed. Bladensburg, with a population of about 10,000, has about 20 police officers.

On its Web site, the fire department described Johnson as “one of the family,” a “great friend” and “great fireman.”

“We shall forever remember the great times and the many things that you have taught to so many of our firefighters over the years,” the site said.