Hydrogen-fueled pollution-free transportation

Hydrogen has been a useful fuel in manned spacecraft, where the only exhaust from the electric power generating fuel cells is useful water. The cost of producing and delivering the hydrogen, though high, was trivial compared to its value in the missions. We have a new problem in our Earth's atmosphere - its growing content of carbon dioxide, 47% of which comes from transportation-vehicle exhausts. Replacing all of the petroleum-fueled transportation with hydrogen-fueled transportation would reduce the carbon dioxide air pollution from transportation to zero. The cost of producing hydrogen during the night by electrolysing water with power from nuclear power plants would be trivial. However, there are added costs in hauling hydrogen in tank trucks to filling stations and carrying hydrogen fuel in cars.