Four people were killed within an hour last night in traffic incidents in the Washington area -- three men in an SUV in Montgomery County and a 6-year-old boy who was trying to cross a street in Fairfax County.

The three men were riding in a Jeep Cherokee heading south on Georgia Avenue in Wheaton when a car crossed the median and collided with their vehicle, sheering off its top, Montgomery police said.

In Fairfax County, the boy was killed about 7:30 p.m. when he darted into Tiswell Drive in Mount Vernon and was struck by a Fairfax Connector bus, Fairfax police said.

The boy was identified by police as Sean Campbell of the 300 block of South Illinois Street in Arlington. He and his parents and one or more other children had just arrived in a van for a family gathering, said police spokeswoman Mary Ann Jennings.

"He apparently darted between two parked cars" and was struck, Jennings said.

Other family members were not identified.

About a half dozen passengers were on the bus at the time of the incident.

A resident who identified herself as Jillene Nikalao said the buses, which are on a regularly scheduled route, drive too fast on the residential street. Another resident, Gina Groves, said, "They zoom through this neighborhood."

Jennings said a preliminary investigation showed no sign that excessive speed was involved in the incident.

In the Wheaton crash, a Mustang was northbound in the 11600 block of Georgia Avenue about 7:15 p.m. when it jumped the curb of an 8- to 10-foot-wide median and collided with the Jeep, police said.

The two men in the front seats of the Cherokee died at the scene; a passenger in the back died at a hospital.

The driver of the Mustang was thrown from his vehicle and taken to a hospital. He was expected to survive, county police said.

Police Lt. David Falcinelli said all possible causes will be investigated, including whether alcohol was used.