If you want to reduce a country's usage of gasoline, then a great starting point is to add a tax to it, as described by Prof. N. Gregory Mankiw. Mankiw feels so strongly about this strategy that he has made it a regular feature on his blog: whenever he reads a public official backing this plan, he enthusiastically marks them as new members of the "Pigou Club".
Personally, I remain unconvinced that we should try at all to cut gasoline usage. Energy is a key part of our wondrous modern world, from computers to factories to transportation to interior climate control. The economic argument against gasoline use does not convince me, because as soon as gas becomes scarce, it will become expensive all by itself. I do not buy the environmental argument because it is simply impractical to stop CO2 growth in that way. I do not buy the national security argument, but rather its opposite: I believe we should eagerly embrace international trade in order to tie the world together more closely.
Nonetheless, if the policy goal is to cut gas usage, then a Pigovian tax is the place to start. It makes the costs obvious as a tax, instead of hidden in regulatory costs and economic inefficiencies. It lets individuals work out the details, instead of trying to find economic geniuses in Congress to act as master planners -- SUV's, anyone?