Ford, Renault-Nissan and Daimler have agreed to jointly develop a fuel cell system to try to speed up the availability of zero-emission vehicles.

BBC: Nissan FCEV on display at a car show in Brussels in January

So, a hydrogen fuel-cell car even running ... on hydrogen derived from natural gas cuts that carbon emission by 60%.

FORBES: Magazine Article

The project to deliver a fleet of the zero emission taxis to the streets of London in time for 2012 is on track, with the first Fuel Cell Black Cabs covering a combined total of over 8, 000 miles in road and test track testing conditions.

ENGADGET: UK's first fuel cell-powered black cab hits the streets of London