Motorcycles, perhaps surprisingly, aren't all that much more efficient than regular gas cars. The tl;dr is that their aerodynamics are terrible, and their engines not tuned for fuel efficiency.

Hmn. Brief research seems to show that you're more correct than I would have expected, but also that it's less true than I think you imply.

For example, https://afdc.energy.gov/data/10310 gives motorcycles as almost 2x as efficient as cars, almost 3x as efficient as "light truck / van".

Given that enormous amount of metal that's not being hauled around, I would have expected a bigger difference. Nonetheless, for single-occupant travel, halving transportation carbon footprint would be quite a great thing.

>Before any new car hits the showroom, the EPA runs an emissions evaluation and calculates a “CO2 equivalent” – a single number that represents GHGs CO2, NO X , HC, and CO. The CO2 equivalent units are in grams/mile, so a higher number means more GHGs and more climate damage. For a 2WD 2020 Ram 1500 HFE on the highway, that number is 340 g/mile. Unfortunately, motorcycle emissions data isn’t documented by the EPA. This is a real issue, because if the problem isn’t measured you don’t know what to fix.

>There are a few independent studies that shed light on the issue, however. One published in 2008 by Swiss researchers took real data from several motorbikes including a BMW R1150GS. The GS highway CO2 equivalent is a stunning 380 g/mile (17% worse than the Dodge)! They found that a 1993 Honda Shadow VX600 with only 583 ccs spews a whopping 408 g/mile. That is twice as much as a new Honda Civic!

>Other studies would suggest the problem is even worse. Global MRV tested out their portable emissions equipment in 2011 comparing 12-motorcycles to 12-cars of varying years (this was featured on an episode of Mythbusters). Motorcycles were almost universally terrible, with motorbikes from the 2000’s producing 3,220% more NOx and 8,065% more CO2 than cars of the same era. California has the largest motorcycle ridership in the country, and in 2008 the LA Times reported that while motorcycles accounted for 1% of all miles traveled, they were responsible for 10% of the state’s smog-producing emissions.

Taken from https://autowise.com/motorcycle-vs-car-emissions/ .

I've had my M1 since 1994, so I enjoy riding, so please don't take this as all negative. But it's important to look at the real data, which is much worse than people think with regards to emissions and pollution.

Many motorcycles didn't come with cats in the 2000s, combined with lots of high strung 600s running massive valve overlap.

But the modern class of commuter bike has got to be pretty good. Drag coefficient is poor but they're also a much smaller area, and city driving is more forgiving for aero.

This is a key point. Fuel consumption on my bike goes from about 22km/l all the way up to 15km/l if I increase my speed from 70km/h to 130km/h. Essentially the killer is wind drag. I'm riding a bike with notably poor aerodynamics, I suppose sport bikes do better in this regard.

Ah, hmn, that is a very good point.

Per my previous comment, motorcycles are more efficient that cars, in terms of consumption of fuel. (though not as much as I'd have thought)

But they're also worse on emissions, which is the public harm that is of greater interest here.

And yikes, those numbers.

It's pretty shocking, isn't it.

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The good news is that as batteries improve, bike like the all-electric Zero line are going to get both more popular and more affordable. I'm looking forward to when I can get one!

This is very surprising. But on reflection I suppose it makes sense, because the typical motorcycle is designed to be a performance machine not a commuter vehicle. So the engineering trade-offs are probably more similar to those made for sports cars.

Yesterday morning just before 6AM we had some sort of maniac coming around entire suburb and reving their bike, just having a joy ride.

I was about to maim him. I hate loud vehicles.