You're right, they've tried everything which comes to mind.

All it's going to take is an energy source which is portable, cheap, light and relatively safe. Someone will come up with a way to utilize it.

When the atmosphere supplies the O2, petroleum and combustion are just too attractive.

I think there's a couple of things operating.

First, the internal combustion engine used the only available energy source and that "drove" the infrastructure, which is now invested in internal combustion.

And the internal combustion engine "drove" the structure of society, allowing people to live a long ways from where they work, a long ways from relatives, and so on. For another power source to be viable it would have to live in the internal combustion world, and that could be tough.

Had internal combustion not been viable societies may not have developed the sprawl.

If you took it away, or severely limited emissions, or rewarded less emissions, or penalized higher emissions, another way to power vehicles would come along, and society would change a bit, I think.

Imagine what life would be like if everyone had to use muscle power or take mass transportation. I think people would structure their lives differently.

Arf