A Texas State Trooper saw the driver park off of the roadway around 10:30 p.m.
That's when the trooper turned around and found the driver near death.
He was rushed to Memorial Hermann Hospital where he is in critical condition.
Police believe the man in his 40s was shot while driving on the beltway.
Investigators found shell casings on the road not far from where he pulled over.
"I've talked to family. We're just trying to piece together what happened. We don't know where he came from. That would be a great starting point," Sgt. Cullen Duncan said. "Anyone who has any knowledge is urged to contact HPD Homicide Division and Crime Stoppers to help us out with this."