@qwazix Induced demand and the Jevons Paradox are real, but I don't think people would have found the time or interest to drive more because their cars were more effective? Isn't most driving commuting?
I can imagine some uses going up, maybe fewer people carpooling if they're doing it purely out of economic necessity, but I don't see how car use would go up by 50%, that's a huge increase.
If gas prices would have gone up to counter efficiency gains, through fuel taxation, car use could have even been kept level.