In Taiwan, motorcycles are a popular mode of transportation. Although motorcycles are a dangerous transportation mode, they still play an important role because they are a convenient means of transportation. Numerous seniors ride motorcycles for their daily activities, especially in rural areas where public transportation is infrequent or nonexistent. There have been numerous serious accidents involving senior motorcyclists occurring in straight lanes, but there are few studies investigating the causalities for this type of accident. This study aims to identify the accident characteristics for senior motorcyclists by analyzing crash data involving elderly motorcyclists from 2006 through 2010. In total, 22,861 (32.5%) senior motorcyclists were involved in accidents occurring in straight lanes, and 17,813 (77.9%) of these were two-vehicle accidents. We investigate two-vehicle accidents to understand their accident characteristics, and our results show that the three major accident types in straight lanes are the following: the sideswipe accident not resulting from an improper turn, the sideswipe accident resulting from an improper turn and the rear-end accident. Based on the analysis results, we provide a summary of safety concepts for senior motorcyclists to increase their safety awareness and help them avoid traffic accidents.