Abstract
Public transport policy is based on calculations using models, which are often undertaken by external firms. Therefore, the public transport company is often unable to collect sufficient data about their own market. In particular, behaviour in transport is often a "black box" for the users of model studies. The Rotterdam Tramway is able to estimate the necessary data about transport modes combining the results of interviews to their commercial data. The extent of such a study can be limited by working with relatively little origin destination zones. Because mobility behaviour per motive and per target group differ very much, this should be taken into account when the parameters are estimated.