The California Highway Patrol said a gas can was found at the crash site. Authorities think the two victims, a man and a woman, pulled over because one vehicle was low on fuel.
Both drivers were waiting outside their vehicles when a big rig veered onto the shoulder of the freeway, just before the Gary Avenue onramp, and struck them around 3:15 a.m.
The man was thrown off the freeway onto Gary Avenue, where he succumbed to his injuries. The woman was found dead at the crash site.
All eastbound lanes were shut down at Reservoir Street and diverted to Highway 71 as evidence was collected. All lanes reopened just before 7 a.m.
The driver of the big rig was transported to Pomona Valley Hospital as a precaution.
"As far as the driver of the big rig, he didn't have any visible injuries," said CHP Sgt. Keith Phillips.
It was unclear why the big rig driver veered to the shoulder, but as authorities continue their investigation, they have ruled out alcohol as a contributing factor.
The identities of the victims have not yet been released.
The CHP wants to remind drivers to remain in their vehicles if their cars become disabled and they're forced to go to the shoulder. But authorities said in this case the impact was so severe, the two victims likely would not have survived even if they'd followed that advice.