Video-recorded accidents conflicts and road user behaviour: a step forward in traffic safety research

TNO Human Factors conducted long-term video observations to collect data on the pre-crash phase of real accidents (what exactly happened just before the collision?). The video recordings of collisions were used to evaluate and validate the safety value of indepth accident analyses, road scene analyses, and behavioural observations (including traffic conflicts). Digital video recordings have been made at four urban intersections for a period between 19 and 22 months (24 hours/day). Collisions and conflicts have been analysed quantitatively using the VIDARTS (VlDeo Analysis of Road Traffic Scenes) approach and conflicts scored according to the criteria of the DOCTOR (Dutch Objective Conflict Technique for Operation and Research) technique. In total sixteen collisions could be identified from video, ten car-car collisions, two single-vehicle accidents, two car-bicyclist/moped collisions, one single-bicyclist and one single-scootmobiel accident. For each collision, a detailed description is available of the process just before and during the collision phase. The conflicts that were scored (either randomly during the collision scanning process or systematically for one day) clearly illustrated typical safety problems and resulted in several observations about the typical lay-out and functioning of the intersection at hand. As an example, this is illustrated for one of the four intersections. In general, traffic conflicts and deviant behaviour, together with road scene analyses give a good insight in potential safety problems at specific intersections from a road users' perspective. The collected collisions helped a lot to get a better insight in accident causation processes and to value the results of conflict observations and road scene analyses. With respect to the collisions, remarkably, in most cases, another road user was (in)directly involved, either as a distracting or as a contributing element. Time-related measures such as Time-To-Collision (TTC) and Post-Encroachment Time (PET) are promising surrogate safety measures for analysing encounters between road users at intersections and certainly have potential to serve as predictors of accident risks, for example for the development and application of traffic safety modules in microscopic traffic simulation models.