I've added a Twitter Bootstrap theme and some mobile specific CSS

Not sure if you'd be interested in using it, but here if you want it :)

Really cool idea, would be great to you build on it. In particular being able to get info about carbon footprint usage (especially for regular journeys - e.g. commutes) would be interesting to see. I bet quite a few people would find that useful.

I thought Gary's (@garyshort) idea about using the car tax disc brackets to provide a quick way to broadly estimate CO2 usage for different cars seemed like a good one,