A series of motorcycle/car collision experiments and in-depth investigations involving motorcycle/car accidents with two riders were carried out in order to study the difference in behavior and injuries between the driver and the passenger of the motorcycle during a collision, and to provide general data for identifying their seat positions on the motorcycle in traffic accidents. In all the tests, two Hybrid II dummies were seated on the double seats of the motorcycle as riders. The motorcycle collided against the front door, front end or rear door of the passenger car at a speed of 50 km/h, at impact angles of 60 degrees, 90 degrees or 120 degrees. The speeds of the passenger car were tested at 0 km/h or 25 km/h. With different speeds of vehicles and different impact angles, the difference in rider behavior between the driver and the passenger was distinctly verified by analysis of high speed films. It is possible to distinguish the driver's injuries from the passenger's. The abrasion and/or contusions in the chest, face and groin area were severe for the drivers, but less serious for the passengers. The typical injuries of the driver can be expected in terms of the rider behavior during collision from 25 ms to about 150 ms after starting contact. The data and information can be used to clarify the question of who was driving in accident reconstruction.