Cost of road infrastructure is ~36bn.
Furthermore: you have a state of affairs where you are pretty much forced to own and drive a car to e.g. get to work or move around. You make it reflect its true cost making it impossible to afford for anyone except the rich. What now?
And while there are arguments to be had about negative incentives posed by it with regards to incentivising people to commute farther than necessary, the original basic principle is quite simple: Just as companies are mostly only taxed on their profits, so workers ought to pay their income tax only on the money made after deducting any work-related expenses.
And Germany hasn't solved the cost-of-housing problem, either, so a certain degree of commuting is unavoidable. In fact, recently the housing minister basically declared her defeat by announcing that her latest plan for dealing with that problem wasn't building more where people want to live and can make a living, it was subsidising people to move back to the countryside.