Holiday traffic on the Capital Beltway was backed up for six miles for an hour yesterday afternoon by a three-car collision allegedly caused when a New Jersey man suddenly switched lanes near I-270, Maryland State Police said.

James Goganzer, 19, of Manahawkin, N.J., was driving in an inner loop exit lane for I-270 when the accident occurred about 1:30 p.m., they said. Police said Gonzager steered sharply to his left to avoid taking the exit and his car sideswiped a van.

The van, driven by Roger Miller, 21, of Lexington Park, Md., and a homemade trailer attached to it, overturned, police said, and a third car struck the trailer.

Goganzer suffered minor head injuries in the crash and was in good condition at Suburban Hospital, hospital officials said.

Police said neither Miller nor the driver of the third car, Suzanne Wolpoff, 19, of 6700 Arroyo Ct., Rockville, were injured.

They said each driver was wearing seatbelts at the time of the crash.

The inner loop of the Capital Beltway was closed down from Connecticut Avenue to I-270 while the accident was cleaned up, police said.

Goganzer was cited for making an unsafe lane change and negligent driving, police said.