The effect of traffic safety measures : what we have learnt and what we don't know yet : background paper. (L'effet des mesures de sécurité : Ce que nous avons appris et ce que nous ne savons pas encore.)

The purpose of this session is to present a picture of what has been learned about the effect of various safety meas- ures from experiences of the past, and on this basis to speculate about what we should try to learn in the future and how to do so.