A motorcyclist was killed when his vehicle collided with a dump truck on a busy commuter route in Northwest Washington yesterday, and authorities were forced to close the street during morning rush hour, police said.

The accident occurred about 7 a.m. at the entrance to a construction site at Sidwell Friends School in the 3800 block of Wisconsin Avenue NW, police said.

The 28-year-old motorcyclist was run over by the truck and pinned beneath it until firefighters were able to extract him. The man, a Maryland resident, was pronounced dead at the scene. Police declined to identify him pending notification of his relatives.

No charges have been filed, police said. They identified the driver of the truck as James J. Rouse, 57, of Northeast Washington, who works for Harris Contract Hauling of Capitol Heights.

Police said the dump truck was in the far right lane traveling northbound on Wisconsin when it pulled into the middle lane to make a right turn into the construction site. The motorcycle driver, who was heading north in the middle lane, swerved, lost control and slid underneath the truck, police said.

The dump truck might have been stopped in the far right lane waiting for other construction traffic to move before it made the turn into the site, police said.

Police shut down traffic on a stretch of Wisconsin for almost four hours as they investigated the crash and cleared debris. The shutdown forced cars onto side streets, clogging those roads throughout the morning.

Sidwell is building a parking structure, renovating its middle school and expanding athletic fields.

Stanley Manvell, vice president of safety for James G. Davis Construction Corp., the lead contractor on the Sidwell project, said that construction officials do not believe Rouse did anything wrong. He said that the motorcyclist was trying to pass the truck in the bus lane when the vehicles collided.

Rouse "is really broken up about it," Manvell said, adding that the truck driver was hospitalized after the crash because paramedics were concerned about a high blood pressure reading.

Harris Contract Hauling could not be found in phone books or company directories or on the Internet. The company apparently was working as a subcontractor for the excavation firm Goldin & Stafford, Manvell said.

Ralph Goldin, the excavation company's president and owner, declined to comment.

Ellis Turner, an associate headmaster at Sidwell, said he had no further details on the accident. He said the motorcyclist was not a student or school employee.

"We do offer our heartfelt condolences to the family of the motorcyclist," Turner said.