It happened Monday just before midnight between Bissonnet and the Beltway. The road was closed for several hours but has since reopened.
Two brothers were parked on the service road, according to Sgt. David Rose with the Houston Police Department.
"They were not fighting. He was upset, having some emotional problems with a past relationship and some other things," Rose said.
That's when the man threw a pallet into traffic and ended up on the mainlanes of the freeway. Police said as a result, a white pickup hit the man and drove off.
Officers are still looking for that driver and say the truck should have front-end and windshield damage.
Several other cars were also damaged by the debris from the pallet.
The man killed was in his early 20s, police said.
Police said they were going to watch surveillance video from a strip center behind where the brothers parked to try to learn why the man threw the pallet.