CarSafe recognizes five types of dangerous driving events . For each type, we describe the series of rules used
to interpret the low-level state inferred by the classifiers described
in §3.2 that allow dangerous events to be detected.
Drowsy Driving (DD). We adopt a standard metric for measuring
alertness, PERcentage of CLOSure of the eyelid – called
PERCLOS , which more formally represents the proportion
of time within one minute that eyes are at least 80% closed .
This driver state information is provided by the driver classification
pipeline detailed in §3.2.1. CarSafe continuously computes
PERCLOS and declares the driver “drowsy” if PERCLOS exceeds
a threshold (28%) guided by prior studies .
Inattentive Driving (ID). Two types of inattentive driving are
monitored by CarSafe. In the first case, the output of the face direction
classifier is tracked. If the driver’s face is not facing forward
for longer than three seconds while the car is moving forward (i.e.,
while a positive speed is reported by the car classification pipeline)
and not turning as reported by the turn detector (also reported by car
classification pipeline) then a dangerous driving event is inferred.
We use a three second threshold based on the guidelines provided
by . In the second case, we monitor the turn detector. Each time
a turn is detected the historical output of the face direction classifier
is checked. If there is no a head turn corresponding to a car turning
event then the driver did not check that the road is clear before
turning – as a result, a dangerous event is inferred.
Tailgating (TG). We adopt the calculation for a minimum following
distance from [16], which relies on the speed estimation
made by the car classification pipeline. This estimate of a “safe
following distance” is compared to the estimated current following
distance also provided by the car classification pipeline. If CarSafe
determines the safe following distance is not respected for a period
longer than three seconds a dangerous driving event is inferred.