Motorcycles

Myth busters did an episode on this. They found the fuel consumption was less in the motorcycle, but the pollution created was worse.

https://mythresults.com/bikes-and-bazookas

Riding a motorcycle contributes less to air pollution than driving a car from the same time period.

BUSTED

Adam and Jamie chose one car and one motorcycle apiece from the 1980s, 1990s, and 2000s. Adam drove each vehicle for 30 minutes in the city and on the freeway, using sensors to measure the tailpipe emissions. In every case, the motorcycles gave higher fuel efficiency and lower carbon dioxide emissions than the corresponding cars. However, the cars performed better in terms of emissions of hydrocarbons, nitrogen oxides, and carbon monoxide.

At this point, Adam and Jamie decided to try and improve a motorcycle’s aerodynamic performance so that it would use less fuel and give lower emissions. They built a teardrop-shaped shell to cover the entire vehicle, with a tubular steel frame and heat-shrink plastic sheeting. Jamie then drove simulated city and highway courses at Naval Air Station Alameda on a modern motorcycle, with the shell both on and off. The shell gave the best fuel efficiency and lowest CO2 emissions, but did not perform better than the cars on the other three pollutants. They classified the myth as busted, and Jamie attributed this result to the fact that anti-pollution technology has advanced faster for cars than for motorcycles.