How about at the start of the year you get your mileage checked....the half way through the year its checked and your charged due to how many miles you do, hence using more roads etc ?? just a different scope on things !!
I don't think there's much doubt, bikes are, in the main, tuned for performance, not economy
I was listening to Radio2 on the way home & they were talking to someone from the Motorcycle industry re scrappage scheme for bikes ... according to him , since 2007 when the new laws came in regarding CO2 from bikes thats not the case any more & most new bikes are now lower CO2 producers than thier pre 2007 or thier 4 wheeled counterparts