That's a sunk cost though. When someone gets in their car to drive somewhere, they don't think "this trip is going to cost me $7.50" because they pay for their gas at a different time, they pay for their insurance at a different time, they pay for repairs at a different time, and vehicle depreciation is largely invisible. They don't equate time lost to money lost either.

However, if you have a big visual reminder that the road you're driving on will cost you money as soon as you drive on it, then people will be less likely to either take that route or drive altogether.