This research includes the evaluation of a checklist and on-site screening devices to pre-select drivers suspected of being drug-impaired. The reliability of a limited number of promising on-site screening devices will be investigated. The devices tested will have to be promising regarding both reliability and practicality. In addition to the scientific evaluation of the checklist and the oral fluid screening devices, the time consumption of the selection procedure as a whole (checklist + oral fluid screening) will be evaluated.