The on-the-road driving test examines driving ability on a public highway in normal traffic. Driving performance is objectively measured by on-board computers. The combination of driving in real traffic, which gives the test high ecological validity, and objective measurement of driving performance makes the on-the-road test unique among other driving tests. This chapter discusses the methodology and background of the on-the-road driving test.
Subjects are instructed to drive with a steady lateral position within the right traffic lane while maintaining a constant speed. A camera on the roof of the car records the lateral position of the car. On board computers continuously record the lateral position and speed of the car. The Standard Deviation of Lateral Position (SDLP), i.e. the weaving of the car, is the primary parameter of the driving test. A secondary parameter of vehicle control is the standard deviation of speed.
During the past 25 years the on-the-road driving test has been applied successfully in psychopharmacological research, showing dose-dependent impairment for a variety of drugs including alcohol, antidepressants, hypnotics, anxiolytics, antihistamines and analgesics. Up to now, the on-the-road test has been acknowledged to be the gold standard method to determine drug effects on driving ability.