Robert Flagg / WFAA-TV

DALLAS — A portion of LBJ Freeway was shut down during the peak of the Thursday morning rush hour after a semi-trailer truck overturned.

The accident happened around 4 a.m. in the westbound lanes of the highway between Greenville Avenue and Abrams Road.

The driver of the rig, which was hauling pharmaceutical products, told police he swerved to avoid hitting a dog he saw crossing the freeway, clipped a guardrail and flipped over.

About 100 vehicles on the key artery were stuck behind the wreckage without a way to exit. Traffic on LBJ was backed up to Garland.

A hazardous materials cleanup crew worked for hours to clear spilled fuel from the road surface as other workers emptied cargo from the trailer. The road was expected to be cleared by 9 a.m.

Drivers were urged to find alternate routes until the wreck could be cleared.

The driver of the truck and a female passenger were not injured.

WFAA-TV reporters Alexa Conomos and Cynthia Vega contributed to this report.