The indices i and j represent the transport modes: car, bus, tram, metro, truck and non-
motorized transport. In addition, index j also includes external objects (such as a wall or
a tree) as a category. Index n indicates the severity of the accident. A distinction is made
between fatal accidents, accidents with serious injuries, accidents with light injuries and
accidents with only material damage. X, is the number of vehicle km travelled by transport mode i. t-l;! is the probability that an accident of severity n occurs between transport
modes i and j and in which i is the victim. It is defined as