Effects of Four Commonly Used Tranquilizers on Low Speed Driving Performance Tests


STUDY: Betts, T.A., A.B. Clayton, and G.M. Mackay. Effects of Four Commonly Used Tranquilizers on Low Speed Driving Performance Tests. Brit. Med. J., 4:580-584. 1972.

Site: Departments of Psychiatry and Transportation and Environmental Planning, University of Birmingham, Birmingham, United Kingdom.

Subjects: There was a total of 113 volunteers, mostly students, the first 13 of whom were used in a pilot study testing vehicle handling techniques. They ranged in age from 18 to 30 years, and were free from medical or psychiatric problems. All had valid drivers licenses. Further information regarding driving experience was obtained during the testing.

Method: The 100 nonpilot subjects (50 men, 50 women) were divided into five groups for testing and data analysis: (1) chlordiazepoxide vs. placebo; (2) haliperidol vs. placebo; (3) amobarbital vs. placebo; (4) trifluoperazine vs. placebo; and (5) placebo vs. placebo.

The subjects were tested in groups of six every 2 weeks, with double-blind, randomized administrations. The fixed test procedure was to have the subjects who would be tested during a given fortnight come to a closed-course driving site on Wednesday afternoon. They were given (1) a visual screening test; (2) an Eysenck Personality Inventory; (3) a biographical and driving history questionnaire giving age, occupation, driving experience, mileage, accidents, convictions, and car ownerships; (4) a subjective feeling questionnaire, and (5) an objective assessment. Then, after a few minutes driving the vehicle to be used, they were given an instruction sheet and had a practice session: test 1, 6 runs; test 2, 4 runs; test 3, 3 runs; test 1, 6 runs (see below). At that point each subject was given two bottles containing the appropriate drugs, with instruction on how and when to take them.

They returned to the driving site on Sunday morning, and after completing a subjective questionnaire and having an objective assessment, they completed the driving test: test 1, 3 runs; test 2, 3 runs; test 3, 5 runs. They were then given alcohol in a flavored sugar base, 0.5 g/kg. An hour later, they completed the subjective feeling questionnaire, again took the objective assessment test, and were tested on a Breathalyzer, whereupon the three driving tests were repeated.

The following Wednesday the original procedure was repeated, the second bottle of drugs was taken as directed, and on Sunday the rest of the entire procedure was repeated.

For the three road tests, subjects used a Ford Escort Saloon, 13 ft 0.6 in. long. Test 1 involved driving a zigzag course between five posts set one and one-half times the length of the car and then, in reverse, returning to original starting position. For test 2, subjects parked between two boards set across a curb at a distance from each other of one and one-half times the length of the car. Only three movements were permitted: forward, backward toward the curb, and forward to line up parallel with the curb. Test 3 was a gap estimation test. A gap created by movable posts was adjusted upon instruction from the driver to the minimum gap through which he thought he could drive the car.

Scoring of the measurements was adequately described, and the results were statistically evaluated. When alcohol was administered, the mean blood alcohol concentration achieved was close to 0.05% w/v.

Dosage: Each of four drugs – chlordiazepoxide, 10 mg; amobarbitol, 30 mg; trifluoperazine, 2 mg; and haloperidol, 0.5 mg – was given five times over a 36-hour period. All drugs and placebos were prepared as similar white tablets.

Results: All drugs except haloperidol significantly impaired response to one or more of the driving tests to a 5 percent significance level. There was no certain evidence for interaction with alcohol, perhaps because of the low blood alcohol concentrations reached. Objective assessment showed haloperidol had a significant depressing effect, whereas amobarbital caused a slight euphoria. In evaluating themselves, the subjects felt that none of the drugs had any effect. With alcohol, the subject taking haloperidol felt “‘worse,” whereas those taking amobarbital had a subjective stimulating feeling.

Comment: The measurements made in tests 1, 2, and 3 are more relevant to real-world driving than are the frequently reported tests under controlled laboratory conditions. It would seem preferable to have made tests with subjects taking the drugs at true “abuse” levels, and when alcohol was administered to have some groups attain common “real-world” blood alcohol concentrations of the order of 0.1 to 0.25% w/v.


Selections from the book: “Drugs and Driving”. Robert Willette, Ph.D., editor. State-of-the art review of current research on the effects of different drugs on performance impairment, particularly on driving. National Institute on Drug Abuse Research Monograph 11. March 1977.