It happened around 1:30am Saturday on Interstate 610 at the Ship Channel Bridge.
Police say a man behind the wheel of an Infinity was driving erratically southbound on the loop. At the top of the bridge, he slammed into the back of a Chevrolet sedan, which had two people inside.
The crash ruptured the Chevrolet's fuel tank, causing the car to burst into flames.
The male driver of that car was able to get out. He was taken to an area hospital with burns and other injuries from the accident.
Police say he tried to rescue his female passenger -- his sister-in-law -- but the flames were too large. She died inside the car.
The suspect who allegedly caused the crash was gone by the time investigators arrived.
According to officials, the man called some people to come pick him up. They arrived later and were detained for questioning.
A witness told police the suspect asked him for a ride to leave the scene, but the witness declined. He was last seen running southbound on the freeway.
Anyone with information is urged to call the Houston Police Department.