This past decade or so has seen increased number of passenger-miles traveled by motorcycle in the United States. Yet a closer look at the data shows that since the number of motorcycles registered rose at a faster rate (81%) than did the passenger-miles traveled (59%) between 2000 and 2008, each bike, on average, actually traveled slightly fewer miles in 2008 than it did in 2000. Motorcycle registrations in the United States numbered 4.3 million in 2000 and 7.8 million in 2008.

Geographic reference: United States
Year: 2000 and 2008
Market size: 11,516 and 18,395 million passenger-miles respectively
Source: “Table 1-37: U.S. Passenger Miles (Millions),” Bureau of Transporation Statistics, National Transportation Statistics, available online here.