The milage tax would be unconstitutional. The U.S.C establishment of the commerce clause was just one of several parts of the constitution that forbade states and the federal government from numbering the citizen's rights of passage. While a gas tax applies to fuel that can be used to transport, the direct levy on miles driven is a certain infringement in the peoples rights to move freely about the mention and without encumbrances. It cannot be considered constitutional. At some point SCOTUS needs to step forth and recognize that government is servant of the people, not the other way around.