Linking Behavioral Indicators to Safety : 1 What Is Safe and What Is Not ?

19 20 Safety is defined by the interactions and relationships between road-users, vehicles and the 21 infrastructure. But what is it that determines whether a situation is critical or unsafe? Due to 22 the many disadvantages of analyzing accident statistics, safety is often defined as its ‘output 23 measures’, or proximal or behavioral safety indicators. Examples are speed, speed variability, 24 time headway, SDLP, TLC and TTC. But where do we draw the line, what are good cut-off 25 values for these behavioral indicators? In order to come up with international standards, more 26 research is needed to fill in knowledge gaps. This article provides an overview of the link 27 between behavioral indicators and traffic safety. It also discusses earlier attempts and new 28 possibilities for setting cut-off values. The central research question in a new TNO project is 29 how to link behavioral indicators to what can be qualified as safe or unsafe. This paper is a 30 call to join forces and combine the existing data of naturalistic driving studies and field 31 experiments with new research. There is a need to combine behavioral indicators into one risk 32 factor, and add the link with behavior in specific surroundings. Cut-off values can be the end 33 result of a large research proposal, combining data from alcohol studies, visual distraction 34 data and driver drowsiness studies. 35 36