The accident happened just after 10:00 p.m. Saturday on the westbound Schuylkill, just past the Montgomery drive exit.
Police say a 26-year-old man and his girlfriend were traveling westbound on the expressway in two separate vehicles when his girlfriend's car became disabled.
The man, who was driving a U-Haul rental truck, stopped and got out of his vehicle. He started walking back to assist his girlfriend when he was struck and killed by a Philadelphia Streets Department vehicle.
The city driver stopped at the scene.
There is no word yet on any charges.
Police are continuing to investigate the crash.