There's another impact from this idea - the federal gas tax is the principle source of transportation funding in the USA. The gas tax has been declining in real terms for many years. Transportation interests have been complaining loudly about under-spending on asphalt. McCain's plan means even less for roads.

See http://www.transportationfortomorrow.org/.

Everything is connected.

Maybe it's a sneaky plan to reduce oil consumption by ensuring that roads are in such terrible condition that driving becomes a pain?