Effects of Alcohol on Driving Performance

Effects of alcohol on driving performance
There's abundant scientific evidence for the following:
• Alcohol affects perceptual-motor skills required for safe driving and has been demonstrated to result in poorer
steering control and choice of higher driving speeds
• Young drivers are generally not aware of the dangerous effects of alcohol on driving performance
• Because of this lack of awareness, they fail to compensate for the negative effects by driving more careful, choosing
a lower speed or investing more effort in the driving task
• Which results in a dramatically increased accident risk
Because especially young and inexperienced drivers are unaware of the negative effects of alcohol on driving and they tend to
overestimate their driving skills, a simulation of the effects of alcohol in a driving simulator can be an eye opener for this group,
hopefully resulting in refraining from drinking while driving. A part of the evidence is presented below.
A substantial part of the literature on accidents and driver behaviour concerns the effects of alcohol. The effects of alcohol on
performance are well documented for a large number of tests. Only a few examples are given here. Moskowitz and Robinson
(1986) reviewed the literature on the effects of alcohol on task performance. They analyzed the results of 178 studies that
fulfilled regular methodological criteria. Forty-five percent of the studies indicated impairment at 0.04% BAC (blood alcohol
concentration) or less. The majority of studies reported impairment at below 0.07% BAC. Impairments were found in tracking,
divided attention, information processing, eye movements and psycho-motor skills, especially in tasks requiring skilled motor
performance and coordination. Divided attention deteriorated already at very low BAC levels. Signal detection, visual search
and recognition tasks also showed impairments at low BAC levels. Kennedy et al. (1989) measured the effect of BAC level on
performance in a battery of nine tests measuring motor speed, symbol manipulation/reasoning, cognitive processing speed and
speed of response selection. Performance on eight out of nine tests was strongly and monotonously affected by BAC.
Evans (1991) estimated that 47% of fatal accidents, 20% of injuries and 10% of property damage are attributable to alcohol.
This means that alcohol contributes importantly to traffic accidents with the contribution increasing as crash severity
increases. Evans (1989) concluded that eliminating alcohol would reduce traffic fatalities in the United States by 47±4
percent. Guthrie and Linnoila (1986), suggested that epidemiological studies indicate a disproportionate number of alcohol
related fatal crashes involving young male drivers below 24 years of age. The majority of alcohol related accidents occur during
the weekend, especially at evening hours, and in summer. According to Smiley (1989), alcohol is involved in 62 percent of all
fatal single vehicle accidents.
There is also overwhelming evidence that alcohol affects operational driving performance. Louwerens et al. (1986) studied the
effects of four doses of alcohol in a task where subjects were required to drive with a constant speed of 90 km/h with a
constant lateral position between the right lane boundaries. Standard deviation of lateral position (SDLP) increased in a dose
dependent manner as a function of alcohol. The subjective assessment of driving performance by the driver correlated poorly
with SDLP and BAC level. This suggests that drivers were unaware of performance decrements under alcohol. In a
simulator study with several driving tasks, Stein (1986) found that alcohol increased the number of accidents. Also, in a task
requiring the driver to compensate for windgusts while following a winding road, steering behaviour was significantly affected
by alcohol, and lane position variability was increased under alcohol. No effects of alcohol on mean speed were found, although
speed variability increased under alcohol. Stein and Allen (1986) reported the results of an experiment that aimed to unravel
the effects of alcohol on performance and risk taking. This is important because the effect of alcohol on accident involvement
has often been attributed to an increase in deliberate risk taking. The effects of alcohol on driver behaviour was studied in a
driving simulator and on a closed course. Both methods gave essentially the same results. Alcohol increased speed variability
and the number of times the speed limit was exceeded. As drivers were well aware of the speed limit and the probability of
detection, and since speed feedback was available both visually and aurally, the increased variability suggested decrements in
the driver's perception and/or speedometer monitoring. Also the frequency of running red lights was increased by alcohol. The
subjective probability of running a red traffic light was affected by alcohol while risk acceptance was not affected by alcohol.
Stein and Allen saw these results as evidence that the driver's perception of speed and distance was impaired by
alcohol, and that the drivers were unaware of this impairment. They concluded that the locus of effect of alcohol on risk
taking is on the perceptual level instead of the risk acceptance level.Wilde et al. (1989) investigated the effect of BAC on
performance on a response timing task and a general knowledge quiz. The findings did not support the hypothesis that alcohol
increases deliberate risk taking. A significant increase in overconfidence in the cognitive task was observed under alcohol, but
overconfidence and risk taking were not correlated.
In an on-road study by Casswell (1977) drivers performed several tasks such as overtaking, driving on straight road sections
and curves and through narrow gaps while responding to road signals, traffic signals and auditory signals in a subsidiary task.
Alcohol resulted in increased speeds and poorer tracking performance. In an on-road study of Smiley et al. (1986), alcohol at
0.05% BAC was associated with significantly higher speed on straight roads and in curves. Also, alcohol decreased the number
of peripheral stimuli detected. According to Smiley (1986), in three of the four studies reviewed, where effects of alcohol on
speed were recorded, alcohol was associated with an increase in speed while it significantly affected steering performance in a
number of studies (Smiley, 1989). In a study of Hansteen et al. (1976), alcohol increased the number of cones hit and the
amount of 'rough vehicle handling' while it increased speed. Robbe (1994) tested the effect of alcohol on driving performance
during city driving. Alcohol decreased performance in 'vehicle handling' and 'action in traffic', while speed was
increased. Subjects thought, however, that they had driven as well as following placebo and there was no effect of
alcohol on effort invested in the driving task.
In summary, alcohol strongly affects perceptual and psycho-motor skills as well as performance on the operational level of car
driving. At the same time, alcohol increases speed. It may then be hypothesized that a lack of compensation for impairments in
performance is the cause for the very strong role of alcohol in accident involvement. Evidence was presented that suggests
that drivers are unaware of performance decrements under alcohol. This may be somehow related to the absence of
compensatory speed changes and effort.
Because of these effects of alcohol on a group of drivers that is already more at risk (young and inexperienced drivers), a
driving simulator is an excellent instrument to make young drivers become more aware of the effects of alcohol on their driving
behaviour, see: http://www.rijschool-simulator.nl/driving-simulator.html
The following literature was referred to:
• Casswell, S. (1977).Cannabis and alcohol: Effects on close course driving behaviour. In: Johnson, L. (Ed.), Seventh
International Conference on Alcohol, Drugs, and Traffic Safety. Melbourne, Australia.
• Evans, L.E. (1989). What fraction of all traffic deaths are due to alcohol? In: M.W.B. Perrine (Ed.). Alcohol, drugs and
traffic safety-T89. National Safety Council Chicago, Illinois, 424-430.
• Evans, L.E. (1991). Traffic Safety and the driver. Van Nostrand Reinhold, New York.
• Guthrie, S. and Linnoila, M. (1986). Epidemiological amd laboratory studies on alcohol, drugs, and traffic safety. In:
Noordzij, P.C. Roszbach, R. (Eds.). Alcohol, drugs and traffic safety-T86. Elsevier Sciende Publishers B.V. North-
Holland, 63-70.
• Hansteen, R.W., Miller, R.D., Lonero, L., Reid, L.D. and Jones, B. (1976). Effects of cannabis and alcohol on
automobile driving and psychomotor tracking. Annals of the New York Academy of Sciences, 282, 240-256.
• Kennedy, R.S., Wilkes, R.L. and Rugotzke, R.S. (1989). Cognitive performance deficit regressed on alcohol dosage.
In: M.W.B. Perrine (Ed.).Alcohol, drugs and traffic safety-T89. National Safety Council Chicago, Illinois, 354-359.
• Louwerens, J.W., Gloerich, A.B.M., Vries, G. de, Brookhuis, K.A. and O'Hanlon, J.F. (1986). The relationship between
drivers' blood alcohol concentration (BAC) and actual driving performance during high speed travel. In: Noordzij, P.C.
Roszbach, R. (Eds.). Alcohol, drugs and traffic safety-T86. Elsevier Sciende Publishers B.V. North-Holland, 183-186.
• Moskowitz, H. and Robinson, C.(1986). Driving-related skills impairment at low blood alcohol levels. In: Noordzij, P.C.
Roszbach, R. (Eds.).Alcohol, drugs and traffic safety-T86. Elsevier Sciende Publishers B.V. North-Holland, 79-86.
• Robbe, H.W.J. (1994). Influence of marijuana on driving. Thesis. State University Limburg, Maastricht, The
Netherlands.
• Smiley, A. (1986). Marijuana: On-road and driving simulator studies. Alcohol, drugs, and driving: Abstracts and
reviews, 2, 135-154.
• Smiley, A.M. (1989). The issue of BAC limits: Interpreting findings of experimental studies. In: M.W.B. Perrine
(Ed.). Alcohol, drugs and traffic safety-T89. National Safety Council Chicago, Illinois, 116-120.
• Stein, A.C. (1986). A simulator study of the effects of alcohol and marijuana on driving behaviour. In: Noordzij, P.C.
Roszbach, R. (Eds.).Alcohol, drugs and traffic safety-T86. Elsevier Sciende Publishers B.V. North-Holland, 197-201.
• Stein, A.C. and Allen, R.W. (1986). The effects of alcohol on driver decision making and risk taking. In: Noordzij, P.C.
Roszbach, R. (Eds.).Alcohol, drugs and traffic safety-T86. Elsevier Sciende Publishers B.V. North-Holland, 177-181.
• Wilde, G.J.S., Trimpop, R.M. and Joly, R. (1989). The effects of various amounts of ethanol upon risk taking tendency
and confidence in task performance. In: M.W.B. Perrine (Ed.). Alcohol, drugs and traffic safety-T89. National Safety
Council Chicago, Illinois, 494-499.