10 State 5: Under the influence
Description
Driving under the influence (DUI)—also called driving while intoxicated (DWI) and impaired
driving—refers to the driving of a vehicle by a person who has consumed a quantity of alcohol or
drugs (including prescription medication) that causes him/her to function in an impaired way. If the
impaired driving is due only to alcohol, one also talks about drunk driving. While DUI is obviously
dangerous, it is also illegal in most countries to drive under the influence of alcohol, cannabis (or
marijuana), opioids, methamphetamines, and any potentially-impairing drug (e.g., a psychoactive
drug), whether prescribed or over-the-counter.
A psychoactive drug, also called a psychotropic drug, is a chemical substance that changes a
person’s mental state and results in alterations in perception, mood, and/or consciousness.
Based on their effects, psychoactive drugs can be classified into the three main categories of
stimulants, depressants, and hallucinogens (129; 247). Yet, some drugs may fall under
different categories at different times (for example, cannabis is both a depressant drug and a
hallucinogen drug). Stimulants (e.g., methamphetamines, cocaine) speed up the activity of
the central nervous system, often resulting in the user feeling more alert, euphoric, and
energetic. Depressants (e.g., heroin) slow down the activity of the central nervous system, often
resulting in the user feeling more relaxed, sleepier, and insensitive to pain. Hallucinogens
(e.g., LSD) are psychoactive substances that alter human sensory perceptions in such a
way that the user perceives a distorted reality in which time, space, colors, and forms are
altered.
The substances that are most frequently detected in impaired drivers are alcohol followed by
cannabis. Studies have shown that more than one-third of adults and more than half of teenagers
admit to DUI of alcohol at some point in their lives (8). Alcohol is a depressant drug that affects the
central nervous system and slows down brain functions. Any amount of alcohol can affect a person’s
abilities (1) by degrading attention, perception, information processing skills, memory, reasoning,
coordination, motor skills, and reaction time, and (2) by altering the five senses and the emotions
(9; 14; 163; 63). A person’s alcohol level is measured by the weight of the alcohol in a
specified volume of blood, called blood alcohol concentration (BAC) and measured in grams
of alcohol per deciliter (g/dL) of blood. According to NHTSA, the effects of alcohol vary
with BAC in the way shown in Table 8, in Appendix C, and the risk of having an accident
after consuming alcohol increases exponentially as a function of BAC. For example, every
additional 0.08 g of alcohol per deciliter (dL) of blood multiplies by four the risk of accident
(8). According to the World Health Organization (231), best practice for drunk–driving
laws includes a BAC limit of 0.05 g/dL for the general population and of 0.02 g/dL for
young or novice drivers. Although studies show considerable differences among individuals
regarding their responses to alcohol consumption (33), young drivers experience significantly
stronger effects, putting them at greater risk of accidents (171; 246). Hangovers, i.e., the
after-effects occurring after heavy drinking and as the BAC subsequently approaches zero,
are, however, known to also affect the performance of daily-life tasks, such as driving, by
impairing cognitive functions, such as memory, psychomotor speed, and sustained attention
(69; 221).
Indicators
Several physiological indicators are used to monitor DUI such as heart activity (163; 165),
breathing activity (165), body temperature (163; 183), and pupil width (183). Alcohol is known to
increase HR and breathing rate (165). Cannabis is known to increase HR and breathing difficulty.
Alcohol increases the activity of arteries and other blood vessels, therefore increasing the temperature
of the face of a drunk person (183). The variations of temperature are visible on the nose, eyebrows,
chin, and forehead. When people drink alcohol, their irises become darker, because the sclera is replete
with blood vessels that increase in temperature with alcohol consumption. In a sober person, the
temperatures of the sclera and the iris are the same, but with alcohol intoxication, the temperature of
the sclera increases compared to the one of the iris because of the denser blood-vessel network in the
sclera.
Behavioral indicators of DUI include parameters of gaze (due to the impairment of some visual
functions) and of slurred speech (165). Drunk speakers may use prosodic contours differently from
sober speakers, using more or less speech emphasis. Drunk speakers may pronounce words
differently, choose certain pronunciation variants more frequently than others, and may
even select more frequently certain words, the latter affecting the phonotactic patterns
(189).
NHTSA (157) defines four categories of cues to predict that a driver is DUI, namely problems in (1)
maintaining proper lane position (e.g., weaving, drifting, swerving), (2) controlling speed and brakes
(e.g., varying speed, abnormally driving at low speed, stopping beyond a limit line), (3) maintaining
vigilance (e.g., driving erroneously in opposing lanes, responding slowly to traffic signals), and (4)
exercising proper judgment (e.g., following too closely, turning illegally). In agreement with NHTSA,
which indicates that a drunk driver is prone to weaving, drifting, and swerving (and thus to having
difficulty keeping his/her vehicle in the center of the lane), an increase in SDLP is recognized in the
literature to be an indicator of DUI of alcohol (84; 133; 144) and hangovers (221). Speed and
acceleration are other indicators, as drunk drivers often experience difficulty in keeping an
appropriate speed, with abrupt accelerations or decelerations, erratic brakings, and jerky stops
(84; 144).
The above information allows one to fill, in Table 4, the relevant cells of the “Under the influence”
column.
Sensors
In police operations, alcohol levels are typically measured with a breathalyzer using air exhaled
through the mouth. The amount of alcohol in breath can then be used to determine the BAC (165). If it
is above the legally authorized value, the results can, if desired, be confirmed by a blood test. With just
100 microliter (μL) of this sample, one can, not only measure the BAC precisely, but also identify and
quantify 37 substances that are of interest in the context of drug-impaired driving (92). Many people,
however, drive under the influence without necessarily being stopped and checked by police every
time they do so.
To solve the issue of DUI, the literature commonly suggests the use of ignition-interlock devices
(14; 30; 179). When a driver enters his/her vehicle, he/she must provide a breath sample,
and an alcohol sensor then determines whether he/she is drunk (i.e., has a BAC above
a specified threshold). If this is the case, the ignition-control system prevents the driver
from starting the engine. Ignition-interlock devices are usually installed in the vehicles
of people with prior DUI convictions and in long-haul, commercial vehicles, e.g., trucks
and buses (8). This solution does not, however, allow for the real-time monitoring of the
state of the driver, and does not prevent the driver from drinking alcohol after starting the
engine.
To counter this problem, Sakairi (187) developed a system using a water-cluster-detecting (WCD)
breath sensor that can detect breath from about 0.5 m, allowing one to monitor the driver’s alcohol
level while he/she is operating his/her vehicle. The sensor detects breath by separating
positively-charged water clusters in breath from negatively-charged ones by using an electric field and
by measuring the two corresponding electric currents.
The detection of individuals DUI of alcohol can also be achieved based on the heart activity.
Indeed, Kojima et al. (104) and Murata et al. (149) constructed a seat incorporating an air-pack
sensor that monitors, via a body-trunk plethysmogram, both the heart activity and the breathing
activity. Measurements, during 5 min, of the extracted body-trunk plethysmogram signal, called
the air-pack pulse wave, reveals differences due to the consumption of alcohol, allowing
one to distinguish between sobriety and intoxication. Wu et al. (237, 238) propose to use
a wearable ECG sensor, and an SVM to classify the corresponding ECG data as sober or
intoxicated.
Recognizing whether drivers are DUI of alcohol can also be achieved using a camera that acquires
IR images (79; 106; 143). For an intoxicated person, vessels on the forehead become more active so
that, in an IR image, the intensities of the pixels in this region are affected accordingly. Menon
et al. (143) developed a system that uses IR images of the driver’s face in order to classify him/her as
sober or drunk. The system successively (1) locates the face using a CNN and (2) performs the binary
classification based on differences in blood temperatures at 22 points on the face of the driver using a
supervised-learning-classification algorithm based on a probabilistic model called Gaussian-mixture
model.
Rosero-Montalvo et al. (183) introduce a non-invasive system incorporating a gas sensor, a
temperature sensor, and a camera to identify a person having alcohol in the blood, through supervised
classification of the data from (1) the two sensors and (2) the results of the analysis of the
camera output via computer vision. The authors use the concentration of alcohol in the
vehicle environment, the facial temperature of the driver, and the diameters of his/her
pupils.
According to NHTSA and its four, above-mentioned cues that a driver is DUI, vehicle-based
indicators and related vehicle-centric sensors are of interest. Relevant CAN-bus parameters, and
indicators such as wheel steering and lane discipline, are widely used to detect instances of DUI
(22; 50; 75; 74; 117; 201). Harkous et al. (75) identify drunk-driving behaviors using HMMs based
on car-sensors data, available via the CAN bus. They use wheel-steering parameters, speed, and lateral
position as indicators. They found that longitudinal-acceleration sensors achieve the best average
classification accuracy for distinguishing between sobriety and intoxication. Harkous and Artail (74)
extend the above work by replacing each HMM by a recurrent neural network (RNN). Likewise, Berri
and Osório (22) use features such as speed, acceleration, braking, steering wheel angle, distance to
the center lane, and geometry of the road (straight or curved) to detect DUI of alcohol.
Their system can also be used to detect the presence of any psychoactive drug that can
cause a driver to have abnormal driving behaviors. To detect an intoxicated driver, Dai
et al. (39) describe a solution that only requires a mobile phone placed in the vehicle. Using
the phone’s accelerometers, they analyze the longitudinal and lateral accelerations of the
vehicle to detect any abnormal or dangerous driving maneuvers typically related to DUI of
alcohol.
The above information allows one to fill the relevant cells of Table 5.
Table 4: Detailed “states vs indicators” table, introduced in simplified form in Figure 3. Each
cell in the heart of the table gives some references (if any) discussing how the corresponding
indicator is useful for characterizing the corresponding state.
Table 5: Detailed “sensors vs indicators” table, introduced in simplified form in Figure 3. Each
cell in the heart of the table gives some references (if any) discussing how the corresponding
sensor is useful for characterizing the corresponding indicator. The indicators are identical to
the ones in Table 4, thereby allowing one to link both tables.
