A 17-year-old girl from Brighton was killed instantly Thursday morning when she crashed into a semitrailer on Colorado Highway 7, the Colorado State Patrol said.

Elizabeth Bettles was driving west when her black 1998 Pontiac Sunbird veered outside her lane, crossed the double yellow line and drove right under the rear wheels of a tractor-trailer that was heading in the opposite direction, CSP officials said.

"What we do know is the driver almost suddenly veered into the oncoming lane," said a state trooper on the scene.

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The truck driver, Benjamin Montoya, 31, who was not injured told investigators that he could see that Beetles' head was down -- facing her lap as her car drifted into his lane. Montoya said that he steered his truck off the right side of the road in an attempt to avoid the collision but Beetles' car crashed into the rear of his trailer.

Investigators do not believe that alcohol or drugs were a factor.

Bettles was a student at Brighton Charter school.

The crash occured at about 11 a.m. at Lomand Circle, just outside Brighton in Adams County. The road was closed for several hours, but opened following an accident investigation.