Effects of Alcohol on Driving Performance
Content
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 results in an choice of higher speed. A lack
of compensation for impairments in performance is the probable 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 is probably the cause for 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.
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.
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 results in an choice of higher speed. A lack
of compensation for impairments in performance is the probable 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 is probably the cause for 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.
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.
