world's first purpose-built hydrogen-powered bike could be fitted
with an artificial "vroom" because of worries its silence might
be dangerous. A prototype of the motorbike, which could cost
more than $8,300 (£4,500), was unveiled in London on March 15,
2005. The only problem with the fuel
cell bike, which produces no polluting emissions, is that
it is too quiet and pedestrians can't hear it coming.