Figure 1.

Highway driving test. (A) Subjects drive a specially instrumented vehicle for about 1 h over a 100 km primary highway circuit, accompanied by a licensed driving instructor having access to dual controls. The subjects’ task is to drive with a steady lateral position between the delineated boundaries of the slower (right) traffic lane, while maintaining a constant speed of 95 km/h. (B) A camera on top of the car continuously registers the lateral position of the car on the road with respect to the left lane delineation. (C) The standard deviation of lateral position (SDLP in cm) is an index of road tracking error or “weaving.” SDLP scores increase compared with placebo after the use of many sedating drugs including low doses of alcohol. SDLP, standard deviation of lateral position.