[jdietrich]

Motorcycles and bicycles have a vastly disproportionate impact on improving traffic flow. As traffic density increases, two wheelers fill the gaps left by cars, occupying effectively zero road space when traffic is completely gridlocked. Bikes also occupy very little parking space - five or six motorcycles can fit in the space of a single car.

As pvdebbe points out, motorcycles can be extremely fuel efficient. A 125cc motorcycle or scooter can realistically achieve 90-100mpg. A small motorcycle is much more economical to manufacture than a small car, with about a fifth of the embodied energy. Modern bikes are equipped with catalytic converters and have sophisticated engine management, so produce very low levels of local air pollutants.

Two wheeled vehicles have an essential role to play in solving our current transport problems.

http://www.acem.eu/images/stories/doc/pressreleases/2011/PTW...

[Coding_Cat]

Even if all of this is true and then some, it doesn't change the fact that there are very little motorbikes on the road. Switching to these types of roads, even if it were impossible to ride on for motorbikes might still be a net positive for the environment.

[contingencies]

Not really. In much of Asia, which is most of the world's population, two wheelers dominate. Traditionally bicycles, which was followed by motorbikes in South and Southeast Asia and electric scooters in China.

There's a reason why they continue to dominate, and it's not just the cost of cars (I've regularly seen people riding bicycles worth more than many people's cars here in China) - it's because they're practical! Parking, repair, exercise, lack of traffic congestion, etc.