I think they should just raise the gas tax. Two reasons:

• It's a voluntary user based tax.
• Taxes are the only mechanism that government has to use market forces to reduce demand and encourage efficiency.

Besides, $0.10/gal for an average driver of a vehicle getting 20mpg @15k/miles per year, pays only $75 more for better roads, and hopefully, less time on them. The primary argument against higher gas taxes are that it's regressive (affecting the poor more) and strains small businesses that use vehicles. Both are generally flawed arguments.