Forward collision warning (FCW) systems alert the driver of an imminent rear-end collision with the vehicle ahead. FCW systems are difficult to test and evaluate in a real driving situation and a simulator study can thus be a feasible way of assessing various aspects of FCW systems, such as effectiveness and acceptance. A driving simulator allows for repeated exposure to critical situations, however, there is a risk that repeated critical situations reduce the realism and result in a change in driving behaviour. The aim of this study was to assess driving behaviour during non-critical parts of a driving session that contained repeated critical situations. In a truck simulator 48 professional drivers participated in two driving sessions. The first session aimed at evaluating a FCW system which is reported elsewhere (classified). The second session was a 35 min long motorway drive with two critical and three less critical events. Between all events there was a car following situation. 32 of the drivers had a FCW system while the remaining 16 drivers had no FCW. Mean speed between the events, minimum distance to the vehicle in front in the car following situation, and performance on a secondary task - the arrows task - were used as measures of driving behaviour. In addition, the drivers answered a questionnaire about their driving behaviour.