On June 16, 2009, a revolutionary new city car will be unveiled in London powered by a small fuel cell returning the equivalent of 300mpg.

A new technology company called Riversimple is responsible for the ambitious project and its first vehicle is referred to simply as the Urban Car.

 The electric two-seater draws its energy from a small on-board fuel cell powered by hydrogen. Although the rating of the fuel cell is only 6kW, the car weighs just 350kg, so performance should be acceptable for in-town use. A clever 'ultracapacitor' system stores power for release in 15kW bursts of acceleration, which enabled the designers to size the fuel cell based on cruising power requirements.

Riversimple quotes a 0-35mph time of 5.5 seconds, while the top speed is 50mph. A range in excess of 200 miles is the target for the project, which should be enough for several days' usage by the average dweller of a large city.

An interesting figure quoted for the Urban Car is 'well to wheel' emissions of carbon dioxide. Riversimple reckons that 30g/km is a realistic figure for its city car, which compares favourably with the best current road car figure of over 100g/km (the figures quoted by the car makers is not 'well to wheel', but purely exhaust emissions).

Innovative as the technology is, the company hopes to change the way cars are sold too, with plans to lease the Urban Car over a long time period rather than sell it - and include fuel in the price.

On top of that, the car's development will be conducted in an Open Source manner - usually associated with computer programming and the likes of Wikipedia - in which anyone can tweak the car's design, hence contributing to rapid development of the technology. It is also likely that production will take place in many different licensed sites with regional variations.