This article came up in my internet browsing today:
http://www.theatlantic.com/business/archive/2015/10/driving-true-costs/412237/
linking to this report:
http://www.uspirg.org/sites/pirg/files/reports/Who%20Pays%20for%20Roads%20vUS.pdf
"drivers don’t value the road system highly enough to pay for the cost of keeping it in operation and maintaining it."
"…because user fees are set too low, and because, in essence, people are being paid to drive more, there is excess demand for the road system. If roads were priced to recover even the cost of maintenance, driving would be noticeably more expensive, and people would have much stronger incentives to drive less, and to use other forms of transportation, such as transit and cycling."