But who will build the roads!?
I saw a billboard the other day that said "Advertise here for 75$ a day!". That's over 27,000 dollars a year, and that's only one billboard! I imagine that through advertising, private companies would be able to maintain the road and have plenty of money left over. Without a violent monopoly on roads, opportunity and innovation would flourish!
However, this is just one idea on how to fund the roads. Imagine the ingenuity that would exist when the collective intelligence of the free market is allowed to solve the problem.