HOUSTON -

Houston police are investigating the fatal crash that closed the outbound lanes of the Southwest Freeway for several hours Monday afternoon.

The crash occurred around 3 p.m. on southbound Highway 59 near the Chimney Rock exit.

Officials say a 61-year-old man was killed when his SUV collided with a US Postal Service tractor trailer.

The fiery aftermath left all outbound lanes closed for nearly six hours.

Elizabeth Summerlin, of Houston, was directly behind the two vehicles and exiting the freeway when they collided. She says it happened quickly, but she remembers the crash vividly.

"The SUV came up from behind the tractor trailer, clipped the back corner of it, lost control, flipped onto its side," she said.

Summerlin said she jumped out of her car and called 911.

A picture she snapped with her cellphone shows flames and smoke engulfing the SUV trapped between the semi's cab and the concrete wall of the freeway.

In the chaos, Summerlin also recalls four good Samaritans -- apparently heading from work -- getting out of their vehicle on the freeway trying to help.

"They all jumped out with fire extinguishers and they all ran around the side and tried to do something," said Summerlin. "You could see the white smoke from their efforts."

The driver of the SUV died at the scene.

Police say the driver of the trailer truck was taken to to Memorial Hermann Southwest Hospital with non-life-threatening injuries.