They’re not as bad as cars but they still take up a fair amount of space and pollute (noise, fumes) heavily. A modest discount seems appropriate but they definitely should still cost more than transit.
Seems like it would be easy enough - you register your car, each model has an average and max decibel rating. Your congestion charge includes a factor for that - Harley's pay a bigger markup and EVs pay next to nothing for that particular thing.
It’s too easy to modify the exhaust on a motorcycle, so I don’t think this would be practical. Local laws here are very strict about noise levels, and vehicles are inspected regularly, yet still there are a lot of drivers with modified machines that can wake up the dead when revved.
They do not pollute heavily fume-wise, and most motorcycles other than Harleys or sport bikes with racing exhausts with the dB component removed are not that loud. I get 60 mpg and the engine is efficient. A car gets half or less that mpg, so is 2 to 3X more polluting than a motorcycle when you have 1-to-1 driver/passenger comparison. 2 people on a moto is even better than a car.
Most motorbikes I’ve been near have had significantly more smelly exhaust than a modern car. I don’t think their catalytic converters are as efficient, or maybe they’ve been broken?
Anyway, I don’t think the fees aim to improve pollution, just congestion.
Motos emit less CO2, but more NO, however, most motos are now adopting the EU emissions standards with Euro 5 for motos, so I think that gap is not as bad as when Myth Busters did their episode on it.
Motos are certainly less congestive especially with most cars being single driver and no passengers going into NYC.
If you do the math on the CO2, the emissions per passenger mile is significantly worse for a motorbike than for subway or bus -- regardless of the power source for the train or bus.
But, again, I don't think this proposed fee/tax is aiming at pollution or carbon emissions per se, more at the congestion itself.