Looks like a box girder bridge from the photo I saw.
It depends on who else uses the track. If they share with freight rail, the rails can easily handle a light commuter train at 80mph.
If it’s old track that hasn’t been upgraded, or short line track, I wouldn’t run any passenger trains on at all.
Wrong!! Straight track - yes. Curved -no
Passenger cars are much longer than freight cars, which means the passenger cars are creating a deeper chord when on a freight line curve, opening a higher chance of de-railment.