A 47-year-old woman was killed in unincorporated San Mateo County near Portola Valley Thursday afternoon when she was hit on her bicycle by a big-rig, the California Highway Patrol said.

Lauren Perdriau Ward was riding on Alpine Road at northbound Interstate Highway 280 when she was hit at about 3:39 p.m., the CHP said. She was hit by a 26-wheeler and was trapped under the big-rig, according to initial reports.

She was riding a pink Trek bicycle and died at the scene. Ward was a Los Altos Hills resident.

Both Ward and the big-rig were going west on Alpine, the CHP said.

It is not known how or why they collided, but the point of impact was on the left side of the big-rig, CHP Public Information Officer Art Montiel said.

"We don't know if she ran into the big-rig. It doesn't appear it was making any turns," he said.

The driver's name is Gabriel Manzur Vera, Montiel said. He works for Randazzo Enterprises Inc. The big-rig was carrying heavy equipment from a construction job at Alpine and Sand Hill roads.

Ward's family was notified Thursday night, Montiel said.

The 280 on and off ramps were closed for three hours Thursday night.

Ward, a trained nurse, won state Sen. Joe Simitian's "There Oughta Be a Law" contest after suggesting a bill to add a bittering agent to antifreeze so that children and animals would not be accidentally poisoned.

The law was passed in 2002 and was introduced as a federal bill by Congressman Gary Ackerman (D-New York)in 2004. The "antifreeze bittering" law has been adopted in several states but has not yet been passed federally.

Ward had a letter to the editor about cycling safety published last year in the Los Altos Town Crier:

"Remember what it may be like to ride a bike alongside cars. Most people are not out there to ruin your day by getting in your way. A bicyclist is very vulnerable, like a pedestrian, to any sort of accident."

Investigators are asking for witnesses to come forward. Anyone with information is asked to call Officer K. Nielsen at 650-369-6261.