A Montgomery County woman who got out of an acquaintance's car along Interstate 270 after complaining about his driving was struck and killed on the highway early yesterday. Maryland State Police on their way to rescue her arrived less than a minute later.

Jeannette Jackson, 44, had been on her cell phone with a trooper from the start, telling him that she was stranded, alone, on foot and very nervous along a stretch of I-270 near the Frederick County line.

Despite the officer's instruction that she should stay where she was, Jackson started walking. And when a motorist pulled over and screamed at her to get off the road, she bolted across the southbound lanes, according to state police.

She made it across two lanes before a 1996 Toyota Camry hit her. The trooper in the department's Rockville barracks, who was still on the line with her, heard the squeal of tires and then her phone slam to the pavement.

"It's a real tragedy," Sgt. Mike Brennan said, contemplating Montgomery's 10th pedestrian fatality of the year. Despite efforts to drastically reduce the number, 2004 could end with one of the county's highest pedestrian death tolls.

Jackson, who worked for a mortgage company and lived in Montgomery Village, had spent part of Saturday evening at a function at an Elks Club in Frederick, Brennan said. She and three acquaintances were heading home when Jackson began arguing with the driver.

"He basically told her, 'If you don't like my driving or my car, I'm not going to take you home,' " Brennan said, recounting the details of police interviews with Jackson's companions. She asked to get out and the driver complied, stopping his white Mercedes and leaving her on the shoulder near Route 121. It was just after 2 a.m.

"She was let out just north of a bridge, and she actually walked under the bridge," Brennan said. She could have just stayed there, as the officer directed her, or crouched down off the shoulder to hide safely. She was dressed in a black dress and black shoes. Walking along the highway, "she was completely invisible."

Several minutes into her phone call, Jackson told the trooper that a stranger had stopped and was backing up toward her, Brennan said. In the background, the officer could hear the motorist yell.

Then Jackson started across the dark highway. She had nearly reached the median when she was hit, Brennan said. She died instantly.

Police filed no charges against the Toyota's driver. Their investigation is continuing.