Are motorbikes worse for the environment than cars?

Yes. Catalytic converters and other emissions control devices would clean things up, but they're often too big, too heavy or too hot to install on motorcycles. Motorbikes, they emit less carbon dioxide, but they emit large amounts of nitrogen oxides, so turns out the average motorcycle is 10 times more polluting per mile than a passenger car, light truck or SUV. It seems counter-intuitive, because motorcycles are about twice as fuel-efficient as cars and emit a lot less C02