Ammonia is currently made from natural gas, but it's also possible to make less noxious fuels like dimethyl ether, lpg, and even regular gasoline and diesel from natural gas.

Ammonia might also be made using electricity.

I thought the idea of using ammonia enhanced with hydrogen derived from this process in a regular internal combustion was interesting, but not terribly attractive. Ammonia leaks are serious business, both a fire risk and a caustic burn-your-eyes-and-lungs risk. The exhaust gas would be corrosive too. We might as well use ordinary fuels in ordinary internal combustion engines.

The fuel cell use might be a little more interesting.

Of course, I think the best solution would be for us to abandon the automobile culture entirely. Walking is good for our health, disabled people might have electric legs and other mobility devices, and public transportation systems can be entirely electric.

I agree. But we're raised by our parents and by cultural TV stereotypes to believe automobiles are expected for us. If you can solve the riddle of informing children that pollution and polluting vehicles are not natural and they don't necessarily require them to fit-in in our peer-driven society, then you'll have a winner.

solve the oil fuel problem and the problem of what to do with all the urine. And or would always have access to the product you need to generate hydrogen. At least this is what I've read over the last few years.

One convenient side effect would be if everyone was limited to using only what they could produce. Truck drivers might have a problem with it, but our roadways would be much cleaner.

I like how you think.