This paper discusses the limitations and potential of using an occlusion test to assess visual distraction and the suitability of an in-vehicle information system (IVIS) task for driving. This discussion was expanded from issues raised during a UK workshop on occlusion. The paper describes the research history and empirical foundations of occlusion. It describes some of the occlusion technology and applications for this procedure. Issues concerning the occlusion tasks and the duration and timing of occlusion are presented. The main part of this paper focuses on the priority research considerations for occlusion. The paper concludes with a description of some alternatives to occlusion and future research needs. It is concluded that the occlusion test has some promise, however the empirical basis for occlusion is lacking. If occlusion is to be developed as a metric to determine maximal safe visual distraction, substantial barriers remain.