Abstract
A major part of the everyday practice of traffic engineering is dealing with assumptions. Although quite a few assumptions are based on sound engineering judgements, there are still too many that have not been derived from a sound basis at all. The main part of the publication, is aimed at finding a way to cope with the assumptions. This can be done most effectively by:-Reformulating the assumption into a relevant and better defined problem that can be investigated easily-Gathering facts and figures. -Analysing the relevant data.-Taking a decision about the solution of the problem.