That's the best way to make people switch back to cars imho. Not only does constantly paying a fee increase friction significantly, the same is not the case if you were to use a car you only need to refill every other week or so.

At the end of the day the total number of trips are probably not very elastic, because the price (if it isn't a very high one) usually isn't even a consideration if you want to go somewhere (if it's not that far away anyways).