It takes really high gas prices to get people with cars to switch from driving to transit, so the benefit really has to be somewhere else: time savings, convenience, etc.
My edge case model for deciding whether to commute by regional rail to avoid I-95 traffic or just drive.
High gas prices are not ALL it took to see public transit ridership come back in the US. It also took huge efforts by transit agencies to improve their service or at least not cut it.
Transit service cuts in many cites could throttle this growth.