Here is a link to a youtube video of a car that is running completely on hydrogen.  Not only is the vehicle hydrogen powered, but the hydrogen, extracted from water through electrolysis, is done so with solar energy–no fossil fuels are used to obtain the hydrogen fuel.  This is the only way to get true green auto energy, from the sun.

Here is the video:

There are hydrogen fuel saver systems for cars that supplement gasoline powered engines.  This greatly reduces tail pipe emissions from internal combustion engines.  So this, at least, is a step in the right direction.

But the Tennessee state prof has gone a step further.