It's a process, not an answer.
That's the hardest part of this whole debate: We expect another gasoline to emerge but I don't think we are heading toward another cut & dried answer for powering cars (notwithstanding a really strong lobbying effort by one of the alt fuel advocates that forces our hand as a society).
Rather, we may be heading toward a long period of mixed approaches to powering cars. There's something inefficient about that at the macro level that I suspect is not good for someone's economy (almost certainly that means yours and mine!)
We just finished shooting a series on several of these options and I have to tell you EV's seem to make the most common sense among alt powertrains. But where will that electricity come from? If it weren't for nuclear's P.R. disasters of the 1970's, we might be seeing a nice synergy of battery R&D, nuclear power generation, and electric cars coming to the fore. But no.
The AC electric motor is torquey, highly-developed, quiet (though most acutally make a rather cheap, grindy, unsatisfying sound), very low maintenance and can make a car go like hell. But then there are those toxic, cantankerous batteries.
Hydrogen doesn't *want* to be what it *must* to be to become an effective auto fuel, whether we burn it or convert it. It seems like a cocktail of sci-fi and wishful thinking. And it may be that the various bio fuels are just tepid replacements for a smallish portion of our gas/diesel consumption.
Who knows, maybe we're just heading into the period of the . . gas engine. If we can reduce its fuel consumption as much we've reduced its emissions over the last 30+ years we would make a huge impact on our oil consumption. We must keep cleaning up the emissions even further with hybridization, more advanced catalytic converter technology, more precise fuel metering & engine management, etc.
I recall how clean air standards introduced in the 70's were decried as impossible to meet and thought to be the end of the gas engine, the large car, the V8, etc. We went through almost 20 years of hell as cars lost most of their power and became amazingly unreliable. It was a national R&D program carried out in new car showrooms. It was a bad time. But in the end, the gas engine car emerged as a machine with a degree of relative cleanliness unimaginable in 1970. And faster & more reliable than ever imagined, as well.
Refining the gas engine isn't sexy, and that's a huge knock against that course of action. Carmakers won't be able to polish their brand by doing it, and venture capital won't be chasing young companies doing it. Plus it doesn't get us out of places on earth we'd rather not be. But "fixing" the gas IC engine fits all the *mainstream* comfort zones: Consumers, industry, government, and the capital markets.
Are we absolutely sure the IC engine is at a dead end? I've heard that before.