A twin-engine small plane crashed north of Buchanan Field in Concord yesterday afternoon, striking a car and critically injuring a woman before coming to rest within 100 feet of commuter-choked Highway 4.

The Beechcraft 300 apparently failed to achieve takeoff speed at 3:40 p.m., plowing through a fence and flipping a station wagon on Marsh Drive with its front landing gear.

A woman driving the station wagon was taken by helicopter to John Muir Medical Center in Walnut Creek, where she was reported in critical condition with head injuries.

Motorist Eric Smith was driving behind her and witnessed the terrifying accident.

``The plane just didn't stop. It was taking off but it never left the ground,'' Smith said. ``Ten more seconds, and it could have been me. It happened so quick.''

The unidentified 44-year-old pilot who was flying solo apparently did not suffer major injuries and was out of the plane walking when emergency crews arrived.

Asked what happened, he remained silent and appeared stunned as paramedics loaded him into an ambulance. He was treated and released at a local hospital.

The plane's front tire lay near the overturned, crushed car on a grassy area beside Marsh Drive.

The plane skidded to a stop just west of a Budget rental car office and short of the highway.

``Fortunately, it didn't get out onto Highway 4 commute traffic,'' said Larry Thude of the Contra Costa Fire Protection District.

Federal aviation authorities were expected to arrive at the scene late yesterday to examine the wreckage.

A sign for Aerosmith Aviation was posted in the rear window of the plane, but a company official declined to comment on the crash. The aircraft is registered to King Air Charter in Danville, which does not have a listed phone number.

Buchanan Field officials said the pilot did not file a flight plan.

Cliff Kroeger of the California Highway Patrol said the car was registered to a Martinez resident. Authorities did not identify the injured driver.

Buchanan Field was closed for about 30 minutes before officials reopened the airport. Four helicopters on training flights were unable to land while the airport was closed, but were diverted to an airport in Napa or able to land when Buchanan reopened, said Samantha Hayes, a spokeswoman for the Helicopter Adventures flight school.

The crash area has been the scene of numerous similar accidents, prompting critics to call for better safety provisions around the busy airport.

``Sadly, incidents like these happen,'' said Hal Yeager, a leader of the Pleasant Hill neighborhood group People Over Planes. ``And they remind us that we need to keep sufficient buffer space around our runways. Right now, there isn't.''

Emergency crews (right of plane) wheeled off the pilot of a small plane after he missed his takeoff at Buchanan Airfield in Concord. Chronicle photo by Mike Kepka