While motorcycles are a means of transportation, they are also a type of vehicle that is more vulnerable to serious or fatal injuries in traffic crashes. According to a National Highway Traffic Safety Administration (NHTSA) report, in 2015 a total of 4,976 people were killed in motorcycle crashes on U.S. roads. Also in that year, motorcycles represented only 3 percent of all registered motor vehicles and less than 1 percent of vehicle miles traveled (VMT) in the U.S.; however, motorcycles represented more than 14 percent of U.S. traffic fatalities. Figure 1 shows the trend of passenger vehicle and motorcycle fatalities in the U.S. between 1980 and 2015. Considering the substantial reduction in passenger vehicle fatalities in the last decade, it is important to explore and understand the trend of motorcycle fatalities which has been rising during the same period.