Abstract
This paper describes how the Swedish project DROWSI conducted three experimental studies (which manipulated the level of sleepiness). One study was a simulator study, whereas the other two studies were carried out in real traffic. The purpose of the studies was to search for sensitive indicators of sleepiness at the wheel and to develop drowsiness detection systemsthat combine sensor input to deliver criteria for feedback (warnings) to the driver. The studies have identified a number of promising sleepiness indicators, e.g. a generic lane variability indicator, whch can be includedin sleepiness detection and warning systems.