Captain--
So, basically, the auto makers aren't selling so many SUVs and general 'gas-guzzlers', and in response they're working on making cars that use less gas....

So why pass a law to force automakers to do what they're already doing? This here is the beauty of capitalism--the market responds to the consumers' demands.

Hydrogen is easy to make--run electricity through water (sea water works better because the dissolved salt helps it conduct better, but it's not necessary--and it seperates the water into O2 and Hydrogen.

And nuclear power probably won't last forever--by the time it's run out, though, we'll have something else. Remember, back in 1900 everyone used horses, and there's absolutely no problem now with a shortage of workhorses. Why should we assume that science stopped at the car? By 2100, the internal combustion will probably be as obsolete as the horse and buggy. Not because the government said to make it so, not because it's good for the environment, but for the simple reason that whoever creates a viable alternative is going to be filthy rich.