What happens when a system gets too crowded?  The interstate highway system grew rapidly in the 50's.  Since 1960, growth in road miles has been flat, averaging around 2.6% per decade.  On the other hand, road use as measured in vehicle miles traveled (VMT), has grown at a much more rapid clip.  Our analysis of Federal Transportation data showed a 250% increased in vehicle miles traveled between 1960 and 2000.  During the same period the number of road miles increased by only 11%.  Same roads and more miles = congestion and wear & tear. 

While some of this VMT increase comes from more cars on the road the majority of the growth is in per capita mileage.  For a nice analysis and an introduction to Jevons paradox check this post from metcaffeination.

Recent discussion of a mileage tax is causing a minor political dustup.  There is a summary today in Crosscut by Matt Rosenberg from the Cascadia Center at the Discovery Institute.  A standard reaction to the idea of a tax on miles driven is, " just raise the gas tax and provide incentive to use more fuel efficient vehicles."  As the Crosscut article states, the gas tax "sends poor price signals to motorists".  The article adds that a mileage tax "would clarify the linkage between driving and the needs of a poorly maintained and underpriced system."

It's a safe bet that deliberation on a VMT tax will be protracted and contentious.  Whether or not you agree with the premise of a mileage tax the Crosscut article and metcaffeination post will get you ready to join the debate. 

Executive summary of the National Surface Transportation Infrastructure Financing Commission final report (released on Feb 26).

Portland Transport summary of pilot program tracking VMT.