This paper presents a study on the impacts of horizontal curves on the risk of motorcycle crashes when motorcyclists are riding along curved roadway segments. Three statistical models, using ordered probit regression, heterogeneous choice regression, and generalized ordered choice regression, were developed to evaluate the impacts in terms of injury severity. For developing the models, 494 single-motorcycle crash records were collected at 3,320 curved roadway segments with different horizontal alignment designs for a period of 10 years (2003-2012) in Florida. Results of this study show that, curve radius is a significant factor statistically influencing injury severity of single-motorcycle crashes along horizontal curved roadway segments. An increase of 1000 feet in curve radius will decrease the likelihood of fatalities and serious injuries by 0.2% and 0.15%, respectively, in a single-motorcycle crash along a curved roadway section. Speeding is the most significant factor that is more likely to increase injury severity of single motorcycle crashes along a curved roadway segment. Speeding tends to increase the risk of fatalities in a single-motorcycle crash by 10.84%. Good light condition is an effective factor to reduce the risk of fatalities and serious injuries on curved roadway segments because it can improve motorcyclists’ sight distance. Hit-on a fixed object is very dangerous to motorcyclists when they are riding through a curved roadway segment. Other significant factors include roadway surface width, speed limit, use of helmet, and riders’ characteristics. Some recommendations are also given based on the conclusions to improve safety performance for motorcyclists on curved roadway segments, including training/educational programs, lowering down speed limit on curved roadway segments, and installation streetlights.