Teresa Wallendjack said she saw the white Subaru Outback station wagon whiz past her car, its back end fishtailing as it descended a curvy hill on East West Highway.

"There's an accident waiting to happen," Wallendjack, 46, recalled telling her two daughters, 9 and 16, hoping they would remember the warning when they started driving.

The station wagon swerved left and then right in front of her, Wallendjack said, then suddenly spun into oncoming traffic, its tires screeching before it struck a pickup truck and flipped on top of the truck and then a car in what sounded like an explosion.

"He's goofing around!" Wallendjack recalled telling her daughters as they came upon the collision, according to her testimony yesterday in Montgomery County juvenile court. "He's killed these people, and they didn't do anything wrong. They were just in the wrong place at the wrong time."

Montgomery County prosecutors presented Wallendjack yesterday as a witness to what they called the "grossly negligent" driving of Michael Schoenfeld, 17, that started at Bethesda-Chevy Chase High School and ended about a half-mile away in the deaths of two of his teenage passengers and a salesman driving between appointments.

Schoenfeld is charged with three counts of vehicular manslaughter and four traffic offenses in the deaths of Matthew Waymon and Irn Williams, both 16, and John Francis Wert, 40, of Potomac, last July 14. Prosecutors say Schoenfeld drove 68 mph in a posted 30-mph zone and purposely swerved his car while driving five friends home from summer school.

Schoenfeld's attorney, David Driscoll, told District Judge Eric M. Johnson in opening arguments Monday that the collision showed only that Schoenfeld was a young, inexperienced driver who lost control of his car. Schoenfeld, who was 16 at the time and had gotten his driver's license two weeks earlier, has pleaded "not involved," the juvenile court term for not guilty, to all of the charges.

The particular section of East West Highway--a winding, downhill stretch of undivided, four-lane highway linking Connecticut and Wisconsin avenues--also seemed on trial yesterday as Driscoll cross-examined Majid Shakid, an assistant director of the Maryland State Highway Administration.

Shakid, who testified earlier that the lanes on East West Highway are slightly narrower than on some roads, told Driscoll that a recent three-year study found that the highway has more accidents than similar state roads.

"It makes it a little more dangerous road if people are speeding and the lanes are narrower?" Driscoll asked.

"The driver also has a responsibility," Shakid answered.