Originally Posted by Corey872
Then there is the minor issue that water vapor (result of burning hydrogen in your engine) is itself a greenhouse gas, so if you are willing to put aside the global warming hysteria and pump it directly into the air, that is one option. You could condense it and just let it drip onto the ground - although it would probably be like driving in a permanent rain storm with thousands upon thousands of cars running down the road with a constant drip coming out of the tailpipe. I suppose you could trap it in a tank and dump it at every fueling like dumping an RV toilet, but that doesn't sound like much fun.
While I mor or less agree with rest of your post, this paragraph is mostly non-sense.
The issue of the water vapor is really non-existent, or irrelevant. First, for starters, a usual fuel (i.e. gasoline) actually contains more hydrogen atoms than carbon atoms, so a significant portion of the exhaust is already water, and as far as I know, it's not making roads excessively wet. You might argue that twice or thrice as much water would cause problems, but I don't think that would be the case.
As for water vapor being a greenhouse gas, while that's true on paper, the amuont of water in air is not dependent on human activity (except on a very small and local case) since other, natural effects dwarf the amount of water released in the air as a result of a human activity; and on top of that, excess water from the atmosphere will normally precipitate out in a very short amount of time.