see, i think a better solution to the road issue would be a flat national gas tax that covers all roads (US and state highways). with the national tax, it could be lower overall, but still generate the total ammount of funds.
individual state taxes on gas would then pay for town roads, and all the others. again spreading it out would ease the burdon.
but i do believe the national should pay for the highways (some highways are 2 lane roads, like 41 going from up north all the way to florida)
also, gas tax monies can not EVER go for anything else, if there is a surplus it is divided nationally. if there is a surplus 2 years in a row in the same area, the taxes are lowered by law.
to prevent highways depts from wasting money to ensure the same ammount next year, you gave the answer. private contractors, in bidding wars.