Are motorcycles the obvious environmental choice? It depends.

The European Union is considering fuel economy regulations for motorcycles, an idea which, at first glance, seems like a bit of overkill.

(Image: BMW's 1092cc K1100RS, which the BMW website says has a fuel economy of 5.8 liters per 100 kilometers at 120 kph, which works out to 1.5 gallons per 62 miles at 74 miles an hour, or about 41 miles to the gallon. Credit: BMW.)

The initial proposed regulations are for exhaust pollutants other than greenhouse gases, but clearly, that could be the next step.

Seems odd, since one might be forgiven for thinking that cycles would be the clear environmental choice over any car, given the reduced road friction of two wheels, reduced engine sizes, reduced vehicle weight and so forth.

Would a Hawai'i highway be more energy efficient it it were filled with bikes instead of cars?

Well, it's complicated.

(And as we'll see a little later, a lot of the complication deals with how many individuals are on board the bike or riding in the car.)

Turns out, for example, that if you set a 2007 Harley-Davidson Road King Classic next to a Toyota Prius, the Prius wins the straight mileage calculation. The Harley is listed at 32.5 city/45 miles a gallon highway, while the Prius comes in at 51/48.

But that might be a little like comparing a Clydesdale to a Shetland pony. From some perspectives, the Harley is a big, gorgeous, powerhouse road warrior, and the hybrid Prius a prim, schoolmarmy fuel sipper.

Within the motorcycle category, there is plenty of variation, and often it falls in predicable areas. Engine size, for example.

The Honda Shadow Spirit 750 from 2005 gets 50/55 on the mileage scale, while its little brother the Honda Rebel 250 gets 73/86. Yamaha's 125 gets 90/99.

Yeah, size matters. The big issues are how big the engine is, how heavy the bike is, and how you drive it. Certainly, manufacturers' engine design is a factor as well, along with tire design, wind resistance and lots more. This article at MotorcycleCruiser nicely reviews the issues.

The upshot, oddly, is that on a per-passenger-seat basis, fuel-efficient cars are often more efficient than motorcycles.

But if you're riding to work alone in your car, then almost any option (walk, bicycle, motorcycle, bus, carpool) is a better option from a fuel and climate perspective.

© Jan TenBruggencate 2010