There was a total of 6,678,958 motorcycle registrations in 2006, which was the most recent study done by the United States Department of Transportation. This number is the closest indication to how many people are riding motorcycles, and throughout the study, the number continued to rise, which suggests the number could be significantly higher today, according to the Bureau of Transportation Statistics.
The total number of motorcycle riders is a difficult number to determine because the definition of a "motorcycle" is somewhat fluid. The Department of Transportation determined its numbers by using two- or three-wheeled vehicles that were designed for on-road purposes. However, there could be a large number of motorcycle riders who are riding their vehicles off-road or on private land.
The 6,678,958 figure of motorcycle registrations had been a 75 percent increase from a similar study performed about 10 years earlier in 1997, according to the Bureau of Transportation Statistics. Furthermore, all motorcycle sales increased from 2007 to 2008 except for on-highway style vehicles, which could be attributed to the spike in gas prices in 2008. These numbers suggest that motorcycle use was quickly rising throughout the late 2000s, and the vehicle registration study will be performed again in either 2016 or 2017.