The way in which road usage is priced and road infrastructure is funded in the United States has become unsustainable. Support is growing for a Vehicle Miles Traveled (VMT) fee to encourage efficient road usage and replace fuel taxes as the primary funding mechanism for road construction, operations, and maintenance. This paper addresses some questions about a VMT fee including what functions it should perform, how finely it should be differentiated, and how users are likely to adapt to it. To implement an efficient VMT fee, it will be necessary to overcome various technological, legal, institutional, and public acceptability barriers. Copyright (c) 2010, Wiley Periodicals, Inc.