There are new options with very nice specifications and these would be problem-free while the number of sold units doesn't surpass a certain threshold. Try to imagine a city with 20 million of machines producing water vapor, creating a great set of problems related to humidity. Metals, bones, lungs, microorganism development, condensation, actuating on climate and temperature.
It's obvious that any new technology for vehicles should account with the vast quantities of byproducts that could be emitted. The reality of polluted cities and measurable atmospheric or oceanic pollution are a good evidence of what could happen if nobody thinks in the future.
Electricity coming from renewable sources doesn't emit pollution, so it's the unique and only choice today. Magnetism or gravity as well; they are related but still there aren't motors in production.
The same for energy contained in molecules or atoms. Starting a process of consumption that leads to exhaustion and interrelated issues without first using the energy that comes from the Universe, it's more than irrational, with no intelligence!