A California Highway Patrol officer was struck and killed Sunday when a car veered onto the shoulder of the freeway during a traffic stop in San Bernardino County, authorities said.

The incident happened about 3:40 a.m. when two officers stopped a vehicle for speeding on the northbound 15 Freeway one mile south of Hodge road near Barstow, CHP Officer Mario Lopez said.

A 2009 Pontiac G6 traveling north clipped the right rear of the patrol car and struck Officer Justin McGrory, of Victorville. He was airlifted to a hospital where he died of his injuries.

The driver of the Pontiac, 18-year-old Rafael Garcia of Las Vegas, was arrested at the scene on suspicion of vehicular manslaughter.

Circumstances of the collision are still under investigation, Lopez said. Nobody else was hurt.

McGrory, 28, joined the CHP in 2007 and was assigned to the Barstow area office. He is survived by his wife, a 7-year-old daughter and two sons, ages 4 and 1.

I-15 north was closed for nine hours after the accident and traffic was diverted to National Trails Highway.

Governor Arnold Schwarzenegger expressed condolences Sunday at the death of McGrory.

"He was selfless and dedicated, and committed his life to protecting the safety of all Californians," Schwarzenegger said in a written statement. "We extend our thoughts and prayers to Justin's family, loved ones, and the entire Victorville community as they mourn the loss of a father, son and outstanding officer."