Twenty subjects completed an on-the-road driving experiment, consistin
g of two different tests conducted on two separate days. A two-part te
st was administered while subjects were under the influence of alcohol
(BAC < = 0.05%); a four-part test was administered without alcohol co
nsisting of a 2.5 h driving test under vigilance conditions on a quiet
highway. The order of the tests was balanced across subjects. Changes
in relevant physiological parameters, such as ECG and EEG, reflected
changes in driver status and predicted driving impairment. Impairment
of driving performance was measured in a standard driving test (SD lat
eral position and SD steering wheel movements) and in a recently devel
oped car-following test (reaction to speed changes of a leading car).