The purpose of this work is to evaluate the effect of a specific motorcycle licence, held by car drivers, in responsibility for motorcycle-car crashes. The data were provided by a multicentric case-control study (MAIDS) regarding the risk of crash and serious injuries of motorcyclists. A non-parametric method, classification and regression tree (CART), was used to accomplish the objective, and then compared to standard unconditional logistic regression. Drivers owning a motorcycle licence turned out to be less responsible for motorcycle-car crashes than drivers who do not have one; both types of analysis are consistent with this result. It is reasonable to assume that car drivers who hold a motorcycle licence have acquired more ability in riding and controlling two wheeled vehicles than drivers without a licence, and this may help them in predicting motorcycles manoeuvres.