Abstract
A recent study of the Dutch Economics Institute (NEI) presents an analysis of the (backgrounds of the) various models for (calibration of) trip distribution. As is emphasised in this article, the formalisation of every Origin Destination (O-D) matrix estimation technique presupposes a number of mainly implicit choices. Some notes are presented that may be useful for the development of new models and the adjustment of existing models. Besides that, developing standardized test problems for model evaluation in several synthetic situations may produce practical prioritizing estimation techniques.