Motorcycles are environmentally friendly, emitting much less CO2 and pollutants per mile than almost any automobile. In addition, they are a lot more fun to ride!!
John's Harley-Davidson Custom Sportster gets about 47 MPG in city driving and nearly 60 MPG when there are no stop lights.
Deane's Suzuki Boulevard S50 gets slightly better mileage than John's HD, weighs about 100 pounds less, and is more reliable. (But it's not a Harley!)