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Age and Ageing 1999; 28: 59–66 1999, British Geriatrics Society
The effects of age and alcohol
intoxication on simulated driving
performance, awareness and
self-restraint
WARREN C. QUILLIAN, DANIEL J. COX, BORIS P. KOVATCHEV, CHERALEE PHILLIPS
Department of Psychiatric Medicine, University of Virginia Health Sciences Center, Charlottesville, VA 22908, USA
Address correspondence to: D. J. Cox. Fax: (+1) 804 924 0185. Email djc4f@virginia.edu
Abstract
Aims: to investigate whether, compared with middle-aged men (aged 30–50), older men (age 60) (i) perform
more poorly on a driving simulator and (ii) are more sensitive to the effects of ethanol in terms of blood alcohol
concentration (BAC) and driving performance, but more aware of their driving difficulties, and therefore exercise
better driving judgement.
Methods: 14 healthy middle-aged men (mean age 36 years) were compared with 14 healthy older men (mean age
69 years) on an interactive driving simulator, while sober and while legally intoxicated (BAC > 80 mg/dl).
Results: older age was associated with poorer driving performance on the simulator. While sober, older men
exhibited more improper braking, slower driving, greater speed variability, fewer appropriate full stops and more
crashes, and spent more time executing left turns (across oncoming traffic); all values 0.02. BACs 80 mg/dl
were associated with impaired driving, with more inappropriate braking, fewer appropriate full stops and more
time executing left turns (all values 0.02) and trends towards more speed variability, more low speed collisions
and more wrong turns (values < 0.1). However, similar ethanol consumption did not produce higher peak BAC or
more driving impairments in older drivers. While there were no differences between age groups in terms of
awareness of intoxication or driving difficulties, older men were unwilling to drive while legally intoxicated
because of fear of physical injury, whereas middle-aged men were more likely to avoid driving when intoxicated
due to fear of legal ramifications.
Conclusion: while both age and legal intoxication affected driving performance, older men were no more
sensitive to ethanol in terms of peak BACs, driving performance or awareness/judgement than middle-aged men.
Keywords: ageing, driving, driving safety, intoxication
Introduction more aware of their limitations and restrict their driving
[14, 15].
Ageing is associated with a loss of visual acuity, Older drivers have more left-turn intersection
constriction of the visual field, difficulty with pro- crashes (crashes while turning across oncoming traffic)
blem-solving and perceptual speed, response slowing, [16, 17]. These require more time to process informa-
decline in ability to divide attention, increased reaction tion, make proper decisions and execute the turn
time and restricted joint movement, all of which impair across three lines of traffic (oncoming and from the
driving ability [1–8]. There is a greater crash fatality right and left). Older drivers tend to make certain
rate in elderly people [9]. Motor vehicle crashes are the judgement errors: they may fail to yield the right of way
leading cause of death from unintentional injury for or overestimate slower velocities and underestimate
those aged 65–74 [10]. faster velocities [18]. In addition, older drivers often
While there are no more automobile crashes per don’t respond to traffic signs [16].
driver with progressing age, there is a marked increase The probability of a crash increases significantly
in the number of crashes per miles driven beyond at 50 mg/dl blood alcohol concentrations (BAC) and
the age of 60 [11–13]. Perhaps older drivers may be climbs rapidly above the legal intoxication criteria of
59
W. C. Quillian et al.
80 mg/dl BAC [19]. Elderly people may therefore have an Our older drivers’ mean MMSE score was 29.1 (SD =
increased crash risk if driving after consuming alcohol. 0.89). They did not differ from our middle-aged sample
However, the older driver may be more aware of in terms of body mass index, years of education,
intoxication and compensate by imposing more self- average number of drinks consumed per week, but did
restraint when driving while intoxicated. drive fewer miles per year. Descriptive statistics for
By comparing middle-aged and older male drivers these two groups appear in Table 1.
under conditions of sobriety and legal intoxication, we
investigated: (i) what components of driving perfor- Procedure
mance are impaired in the older driver, (ii) what Middle-aged and older men were compared on the
components of driving performance are impaired with driving simulator, driving for 20 min while sober and
legal intoxication in these age groups, (iii) whether while legally intoxicated. Sobriety/alcohol conditions
equivalent BACs are associated with greater driving were randomized and counterbalanced and tests were
impairments in the older driver and (iv) whether there separated by 2–5 days. Subjects signed an informed
is greater awareness of legal intoxication and impaired consent form which explained that the study was
driving among older drivers and of more self-restraint. investigating the effects of various doses of BAC on
driving performance, and completed a screening
questionnaire.
Methods The sessions began at 1730 h, during a fasting state.
During the alcohol phase, subjects consumed drinks
containing a 16-ounce ( 475 ml) base mixture of
Subjects grapefruit juice, orange juice and cranberry juice
Fourteen middle-aged men between the ages of 30 and (2:1:1), to which was added 2 ounces ( 60 ml) of
50 (mean age 36.2, SD = 5.8) and 14 older men aged 190 -proof grain alcohol. Subjects were encouraged to
60 (mean age 69.4, SD = 5.2, range 60–77) were consume each drink within 30 min. After the first
recruited through public announcements and phys- drink, breathalyser tests were administered every
ician referral. On average, those in the middle-aged 15 min using the calibrated Alcosensor IV (Intoxi-
group had had a valid driver’s license for the past 19 meters, Inc., St Louis, MO, USA), which gives a reading
years, compared with 51 years in the older group. for BAC that is accurate to within 0.005%. Once legal
Participants had to be licensed drivers and occasional intoxication (BAC of 80 mg/dl) was reached, no
consumers of alcohol. Exclusion criteria were: (i) further ethanol was consumed and BAC measurements
history of alcoholism determined by personal history were continued every 15 min until peak BAC was
and the CAGE assessment [20], (ii) concomitant reached (i.e. three consecutive BAC readings demon-
medications that would impair driving or were strating no increase). When peak BAC was reached,
contra-indicated with alcohol as determined by their subjects drove the simulator. Middle-aged and older
physicians and (iii) medical conditions that would subjects consumed similar amounts of ethanol [4.2 and
affect driving performance (also determined by their 4.1 ounces (124 and 121 ml)] over similar lengths of
physicians). Older drivers were administered the Mini- time (58 and 70 min) to achieve similar peak BACs
Mental Status Examination (MMSE) [21]. Scores on the (both 80 mg/dl 6). There were no significant differ-
MMSE range from 0 to 30, where scores of 28–30 are ences between any of these variables. Subjects were
considered normal [22]. kept blind to all BAC readings.
Table 1. Demographic characteristics of middle-aged and older male subjects
Mean value ( SD), by age
...........................................................
Variable Middle-aged Older
........................................................................................................................................................................................
Age (years) 36 5.8 69 5.2
Body mass index 201 44 200 12
Years of education 16.1 1.7 17.0 2.4
Mini Mental Status Examination 29.6 2.0 29.1 0.89
Average number of drinks consumed per week 9.6 7.8 9.4 5.1
Years licensed 19 6.3 51 4.9a
Average miles driven annually 18900 11886 9607 4430a
Average number of self-reported accidents per 1 000 000 miles driven 6.0 2.9
Average number of self-reported moving violations in past 5 years .93 1.6 .36 .5
a
P < 0.01.
1 mile = 1.609 km.
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Intoxication, age and driving
To assess objectively driving in a controlled Subjects were randomly assigned to sobriety–
environment, the Atari driving simulator was used. alcohol or alcohol–sobriety driving sequence. Assign-
This is a closed-loop simulator that generates accurate ment to drive course A or course B was similarly
and sensitive driving performance data. An earlier randomized and counterbalanced during sobriety and
single-screen version effectively detected: (i) the alcohol conditions. The courses were equivalent and
driving impairments produced by 20 min of hypogly- were designed to simulate driving demands of a typical
caemia (2.5 mmol) among type I diabetic patients [23], grade 2 US highway (Virginia Department of Transporta-
which was reliable at repeat testing 3 months later [24] tion). Each 8-mile ( 13-km) course took about 20 min
and (ii) the driving impairments induced by legal to complete. Table 2 lists the driving demands of both
intoxication ( 80 mg/dl BAC) among college students courses.
[25]. The current three-screen version of the simulator The simulator records data eight times a second and
has been used to (i) differentiate visually compromised generates 13 driving performance variables (Table 3).
drivers from controls [8, 26–29], (ii) differentiate Four of these variables reflect steering control, four
Alzheimer’s disease outpatients from age matched reflect braking and five reflect speed control. Because
controls [30] and (iii) correlate driving performance some subjects did not complete the course during the
with age-sensitive cognitive characteristics [31]. maximum 30 min and because the further subjects
The simulator has three 63-cm computer screens drove the more likely they were to encounter a critical
that ‘wrap around’ the driver, providing a 165 visual event, full stops and collisions were calculated accord-
field, along with a programmed rear view mirror ing to the percentage of the course completed for each
depicting rear traffic. The driving environment was person. To incorporate the time spent driving in the
realistic, incorporating a typical-sized steering wheel, opposing lane of potential oncoming traffic and the
accelerator and brake pedals, seat and seat belt. Driving further the driver penetrated this lane into a single
performance feedback was provided to the subject variable, a quadratic function was calculated incorpor-
visually through the three screens that updated at a rate ating these parameters into the variable ‘risk midline’
of 60 times/s, auditorially through quadraphonic (see Table 3).
speakers delivering engine, tyre and road noises and Pre- and post-drive, subjects were asked the
kinaesthetically through the steering wheel and pedal questions listed in Table 4 to assess their perceived
pressure. level of intoxication, ability to drive, willingness to
Before each test drive, subjects were verbally drive and reasons for not driving.
oriented to the simulator before driving a standardized
practice course to familiarize themselves with the
various road conditions and operations of the simulator. Results
The practice course is similar to experimental courses,
but there are fewer road signals and less traffic. During
the practice course, room lighting was adjusted to the Effects of age and BAC on driving performance
subject’s preference to minimize glare on the monitors. We performed 2 (middle-aged versus older men) × 2
After completing the standardized practice course, (sober versus legally intoxicated) MANOVA analyses.
subjects were allowed to continue driving until they Older drivers drove less well on the simulator than
felt fully comfortable operating the simulator. middle-aged men. Age affected speed and braking
Table 2. Driving demands for experimental courses A and B
Frequency
.................................................
Driving demand Course A Course B
........................................................................................................................................................................................................................
Left turns (driver needs to turn left, prompted by a detour sign, at specific stop-sign intersections) 3 3
Red lights (driver needs to stop) 2 2
Green lights (driver has throughway) 4 4
Stop-signs (driver needs to stop) 6 6
Throughway stop-sign intersections (side-traffic stops) 4 4
Speed limit changes (driver needs to change speeds) 11 11
Sudden stops (car in front of driver slams on brakes, object in road comes into view as driver crosses 3 3
crest of hill, car runs red light from left side)
Detours at stop-sign intersections (driver needs to obey detour arrow) 4 4
Encroaching fixed objects (vehicle parked in driver’s lane) 1 1
61
W. C. Quillian et al.
Table 3. Measured driving performance variables and explanations
Variable Explanation
........................................................................................................................................................................................................................
Steering
SD steering Standard deviation of steering wheel rotation
Off road Number of times car travels off road
Risk midline Quadratic risk function that increases the longer and further the car crosses the midline
Wrong turns Number of wrong turns driver makes
Braking
Inappropriate braking Inappropriate braking when car is in 35 mile/h, 45 mile/h and acceleration zonesa
Full stops Percentage of appropriate complete stops negotiated at stop signs and stoplights
Crashes Number of times car in accident while travelling > 0 mile/hb
Bump collisions Number of times car in accident while travelling < 20 mile/h
Speed control
Low speed Average % below speed limit when car is in 35 and 45 mile/h speed zones
High speed Average % above speed limit when car is in 35 and 45 mile/h speed zones
SD speed Standard deviation of speed in 35 and 45 mile/h zones
Stop sign hesitation Average time spent stopped at stop sign
Left-turning time Seconds required to go from a complete stop at the stop line to complete the left turn (across oncoming
traffic)
a
Approximately 55 km/h and 70 km/h.
b
Approximately 30 km/h.
variables (see Figures 1–3). Older drivers (i) drove more bump collisions (F = 3.67, P = 0.066) and more
slower (F = 7.49, P = 0.011), (ii) spent twice the time wrong turns (F = 3.82, P = 0.061).
negotiating left turns (F = 18.13, P < 0.001), (iii) had While Figures 1–3 suggest that alcohol led to
more speed variability (F = 4.02, P = 0.05), (iv) made greater driving impairments in older men, intoxication
fewer appropriate full stops (F = 5.40, P = 0.027), (v) had a significant interaction only on inappropriate
had more inappropriate braking (F = 9.75, P = 0.004) braking (F = 4.82, P = 0.037). That is, older men braked
and (vi) had more crashes (F = 4.32, P = 0.048). inappropriately more often than their middle-aged
Alcohol adversely affected driving performance of counterparts when sober and significantly more often
middle-aged and older men in similar ways, primarily when legally intoxicated.
affecting speed and braking parameters. Overall, legal
intoxication resulted in (i) more variability in speed Subjective awareness while legally intoxicated
control (F = 6.59, P = 0.01), (ii) more time spent negotiat-
ing left turns (F = 5.75, P = 0.024), (iii) more inappropri-
ate braking (F = 9.90, P = 0.004) and (iv) fewer Before driving
appropriate full stops (F = 9.19, P = 0.005). In addition, All the middle-aged subjects versus 93% of older men
although not statistically significant, legal intoxication reported feeling legally intoxicated, while 64% versus
led to less hesitation at stop signs (F = 2.89, P = 0.10), 64% reported anticipating difficulty driving and 64%
versus 71% would choose not to drive (not significant).
Of the 19 subjects (nine middle-aged men and 10
Table 4. Questions asked to assess perceived level of intoxi-
older men) who would choose not to drive a car, none
cation, ability to drive and willingness to drive
of the middle-aged but 40% of the older group would
refrain from driving because they were afraid of
1. Are you legally intoxicated (blood alcohol concentration 80 mg/dl) injuring themselves. A fear of injuring someone else
now? was given as the reason for refraining by 22% of the
2. Would your driving be impaired now? middle-aged men and by 40% of the older group, while
3. Would you be willing to drive a car now? 78% of middle-aged and 20% of older men would not
4. If you are unwilling to drive, what is your primary reason? drive because of a fear of getting pulled over by the
(a) You would be afraid of injuring yourself police and having to face the consequences.
(b) You would be afraid of injuring someone else A cross-tabulation was performed and these reasons
(c) You would be afraid of damaging your personal property for choosing not to drive were significant (Kendall’s
(d) You would be afraid of damaging someone else’s personal
t B = –0.59, P = 0.004).
property
(e) You would be afraid of getting pulled over by the police
for driving under the influence and having to face the After driving
consequences
Eighty-six percent of middle-aged versus 86% of older
62
Intoxication, age and driving
men reported feeling legally intoxicated (not signifi-
cant) and 43% versus 79% would choose not to drive
(P < 0.05).
Discussion
Contrary to expectations, healthy, older, male drivers,
of similar weight, with similar current drinking
behaviour, were not more affected by ethanol—
biologically, psychologically or in their simulator
performance—than middle-aged men. A lack of precise
measurement of body fat composition and a small
sample size may have contributed to these negative
findings.
Consistent with data demonstrating more crashes
per mile driven by older drivers, this study demon-
strated greater driving impairments among older
drivers in speed control and braking, but not in
steering. Specifically, older drivers drove slower, had
more speed variability, spent more time negotiating left
turns, had more inappropriate braking, made fewer
appropriate full stops and had more crashes. In a multi-
centre study comparing 246 male and female drivers
aged over 60, we found similar age-dependent driving
impairments [32].
Inappropriate braking, greater speed variability and
fewer full stops may be partially explained by a decline
in visual and divided attention. If older drivers do not
properly monitor their environment, they may brake at
improper times and fail to maintain a steady speed;
both are potentially dangerous situations if another car
is following too close. Fewer full stops may occur
because the older driver is busy scanning the intersec-
tion and becomes temporarily inattentive to stop
signals.
Older drivers may have less sustained muscle
strength in their extremities, necessary to sustain
steady pressure on the accelerator and timely appro-
priate pressure on the brake pedal. Theoretically,
failure to adequately use the controls could add to
the greater speed variability and more crashes
observed in older drivers. If this is the case, strengthen-
ing exercises may improve driving performance in
older drivers. Loss of visual fields, increased central
processing time, decline in visual attention and
increased reaction times may be responsible for the
increased incidence of crashes in sudden stop situa-
tions: we found an age effect for crashes [where impact
is >20 mile/h ( 30 km/h)] but not for bump collisions
(where impact is <20 mile/h). Some older drivers may
Figure 1. The effects of age and intoxication on speed not respond until it is too late.
variables a low speed (average % below speed limit) and b Consistent with studies showing that older drivers
high speed (average % below speed limit) while car is in 35 are at higher risk at left-turn intersections, older drivers
and 45 mile/h ( 55 km/h and 70 km/h) speed zones and c spent significantly more time negotiating left turns on
left-turning time—time required to go from a complete stop the simulator.
at the stop line to complete the left turn (across oncoming Simulator performance was adversely affected by
traffic). intoxication in middle-aged and older men in similar
63
W. C. Quillian et al.
ways. Overall, it resulted in more inappropriate Before driving the simulator, a similar number of
braking, fewer appropriate full stops and more time middle-aged and older subjects recognized they were
spent negotiating left turns. In addition, although not intoxicated, anticipated difficulty driving and would
of statistical significance, intoxication led to more have refrained from driving. When asked the primary
variability in speed, more bump collisions and more reason for refraining to drive when intoxicated, older
wrong turns. Alcohol’s depressant effects on the drivers were more concerned with physical injury to
central nervous system are likely to be responsible themselves or others, whereas middle-aged men were
for the driving deficits by increasing central processing more afraid of legal consequences. This differential
time, decreasing visual and divided attention and motivation has been recently demonstrated in the use
increasing reaction time. of seat belts by these two age groups [33].
Alcohol intoxication only differentially affected After driving the simulator while intoxicated, more
inappropriate braking in older men. This may be older than middle-aged male drivers said that they
partially because the older drivers tested may have would refrain from driving a car based on their
been healthier, on fewer medications and had more simulated experience (79% versus 43%). Perhaps the
recent experience with alcohol. Different effects of older drivers were able to recognize their limitations,
alcohol may have been detected with a larger sample whereas the middle-aged drivers had distorted percep-
and with a sample who were infrequent users of tions of their driving abilities, failing to accept the
ethanol. reality that their driving was impaired.
Figure 2. The effects of age and intoxication on braking variables a inappropriate braking [braking when car is in 35 mile/h
( 55 km/h), 45 mile/h ( 70 km/h) and acceleration zones], b full stops (% of appropriate complete stops negotiated at stop
signs and stoplights) and numbers of c bumps [accidents while travelling <20 mile/h ( 30 km/h)] and d crashes (accidents
while travelling <20 mile/h).
64
Intoxication, age and driving
Key points
• Men over 60 have a poorer performance on a
driving simulator than middle-aged men.
• Ethanol intoxication is associated with poorer
performance on a driving simulator.
• Ethanol consumption does not affect healthy, older,
male drivers more than middle-aged healthy
male drivers in terms of blood alcohol concentra-
tions, driving performance or awareness of either
intoxication or impaired driving.
Acknowledgements
We would like to thank the AAA Foundation for Traffic
Safety for funding this project, especially former
executive director Sam Yaksich for his continued
support. We would also like to express our apprecia-
tion to Rick Moncrief, former director of research at
Atari Corporation, Milpitas, CA, USA and Duncan
Brown, our computer programmer.
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