Each traffic safety problem can be described on the basis of three principal risk dimensions,
referring to the three most important phases in each accident (before, during and after):
• First dimension: size of the activity which can result in accidents: the exposition; can be
measured in terms of the number of travels, the travel distance and the travel time
• Second dimension: the risk (possibility of a traffic accident) one takes when carrying out the
activity
• Third dimension: the consequence of an accident (casualty, fatally injured, seriously
injured, slightly injured, material damage)