A motorist rammed a car into a vehicle yesterday on the South Capitol Street entrance ramp to the Southwest Freeway, then allegedly assaulted a U.S. Park Police officer and at least four other drivers before jumping off the ramp and landing on a parked truck, Park Police reported.

Arrested was Anthony Banks, 25, of 857 Xenia St. SE, police said. Park Police Maj. Richard Cusick said Banks was charged with assault on a police officer and assault with a dangerous weapon -- a car.

Cusick said the incident occurred about 9:40 a.m. when a man driving an Oldsmobile struck a vehicle on the entrance ramp and both cars stopped, causing a small traffic jam.

Park Police Sgt. Thomas Bradley, dressed in plain clothes and driving an unmarked police cruiser, saw the traffic backup and stopped to determine if there were any injuries in the accident, Cusick said.

When Bradley pulled over, Cusick said, a man "immediately walked over to the car and said something to the effect, 'You're a expletive police officer,' " and struck Bradley in the head through an open window, stunning him. Cusick said the man apparently knew that Bradley was a police officer because of the emergency light and radio in his car.

The man then walked down the ramp toward South Capitol Street, climbed into the cab of a truck and assaulted the driver, got into a fight with a motorcyclist who had stopped at the scene, and assaulted at least two other persons, Cusick said.

The man then threw himself over the entrance ramp railing and fell 33 feet onto debris in the bed of a pickup truck parked in a lot below, according to Cusick and a D.C. police official. The man was taken to D.C. General Hospital, where he was in serious condition with facial injuries and a fractured wrist, authorities said.

Bradley and the truck driver were treated for minor injuries, Cusick said.