(KCEN) --- One person was killed Sunday after two crashes within 30 minutes on the Sam Houston Tollway in Houston.

Constables said the initial accident occurred at 6:03 a.m. when a female driver in a black Nissan Xterra crashed and rolled over on the tollway. A driver in a flatbed pickup truck pulled over to the side of the tollway to help the woman.

About 20 minutes later, Constables responded to a second crash. Investigators said a Toyota Corolla drove over a hill at a high rate of speed. The driver couldn't stop and hit the side of the flatbed truck.

The driver of the Corolla was decapitated and pronounced dead at the scene.

Officials have not yet released the identity of the person killed.