(update) KDKA had more info on their webpage. I cut and pasted the important paragraph below.
The early information indicates there was a disabled vehicle on the Parkway. A second car stopped to assist the disabled vehicle. There were two people out of their vehicles when a third car came along and either hit the two men and threw them over the overpass or they jumped to avoid being hit. Both men fell down onto Second Avenue and struck the pavement and were run over by a passing vehicle.