The coefficient of restitution is an important parameter that must be estimated appropriately by a traffic accident reconstruction expert. Due to the limitations of data collection in this type of reconstruction, the development of appropriate models is required from easily obtainable parameters. We used data from impact tests of the Working Group on Accident Mechanics (AGU Zurich) in collaboration with the Test Centre (DTC) in Vauffelin/Bienne and the insurers Winterthur and Zurich. To our knowledge, these data have not yet been studied to relate the coefficient of restitution to new parameters such as the differences in mass between vehicles involved or the whether the impact has been partially or totally absorbed by elements designed for this task. In addition to the aforementioned factors, we found other parameters that influence the coefficient of restitution, such as the impact velocity (also a factor in previous works) and the age of the vehicles. In previous works, equations were used in order to obtain the coefficient of restitution, but recent advances in vehicle manufacturing techniques mean that these equations must be updated with new parameters that provide results that best fit the impact tests. We also compare previous similar studies on this topic.