Thesis for the Degree of Doctor of Philosophy

Health loss among motorcyclists is a global road safety problem for which innovative countermeasures are needed. While the traditional motorcycle safety approach has focused on protective gear and rider education, the Safe System approach adopted in Sweden and other countries implies that the road, the vehicle and the road user, in conjunction with a safe speed limit, should interact to create a safe road transport system. Motorcycles are intrinsically unstable vehicles and the most likely consequence of instability is the rider becoming separated from the motorcycle. In this case, the only countermeasures to avoid health loss are the rider’s protective gear, or a forgiving road infrastructure. The overall aim of this thesis is to understand the chain of events leading to crashes involving motorcycles with Antilock Braking Systems (ABS), compared to similar motorcycles without ABS. This resulted in five studies based on real-life crash data from Sweden, Norway, Spain and Italy. The integrated chain of events was used as a theoretical framework: the chain of events leading to a crash is no longer seen in separate blocks; rather it is a process in which one factor in the early phases of the chain can affect the following ones, thus creating conditions for other countermeasures to be effective. The findings indicated that Motorcycle ABS reduced emergency care visits by 47%. The severity of the crashes that did occur was lower, which reduced the overall risk of sustaining impairing injuries, although leg injuries were not addressed to the same extent. It was also found that almost 90% of fatal crashes with ABS were upright. This result suggests that leg injuries can be addressed by motorcycle design. An example with a specific design (i.e. boxer-twin engine) was analysed, showing that leg injuries were reduced by approximately 50%. Finally, it was found that the overall reduction of injury crashes with ABS ranged from 24% in Italy to 29% in Spain and 34% in Sweden. Essentially, it is suggested that Motorcycle ABS prevent crashes from occurring in the first place, and they also increase stability and change the phases following critical situations, making crashes that do occur more predictable. Therefore, improving motorcycle stability with ABS can create the conditions for making other safety systems more effective, motorcycle crashworthiness, for instance. It is also shown that these findings are feasible in different riding conditions and environments. This thesis can be considered a first step towards a Safe System approach for motorcycles. A more stable, ABS-fitted motorcycle provides the foundation for developing further countermeasures based on ABS. However, further research is needed to design and implement a Safe System that can address health loss among motorcyclists. While motorcycle manufacturers ought to immediately engage in a wide fitment of ABS in new motorcycles, the development of other technologies to improve stability, for instance Electronic Stability Controls (ESC) for motorcycles, will likely have significant benefits. Furthermore, the development and testing procedures of future road barriers will need to have greater focus on upright crashes, and the possibility of interacting with protectors integrated in the motorcycles. The development of motorcycle crashworthiness can be encouraged by consumer testing, i.e. the European New MotorCycle Assessment Programme (Euro NMCAP). Injury risk functions form the basis for the design of a Safe System, where the speed limit and crash protection are strictly connected. Such functions need to be developed for motorcyclists, and further research in this area should be prioritised.