Driver Drowsiness Detection and Measurement Methods - Driver Drowsiness Detection: Systems and Solutions - page 6

Chapter 2
Driver Drowsiness Detection and Measurement
Methods

There are several different ways to detect and measure driver drowsiness
(or sleepiness). They are normally grouped into five categories: subjective,
physiological, vehicle-based, behavioral, and hybrid. This chapter provides a brief
survey of driver drowsiness detection methods in each of these categories.

2.1 Subjective Methods

Sleepiness can be explained as a physiological need to combat the fatigue of the
human system. The more the system is fatigued (i.e., sleep deprived), the stronger
the need for sleep, which suggests that sleepiness can have different levels. Scientific
organizations such as Laboratory for Sleep [ 45 ], Division of Sleep Disorders [ 45 ]
and Association of Professional Sleep Societies [ 7 ], to name a few, have been
creating various descriptive scales of sleepiness levels.
Current subjective tools used for the assessment of sleepiness are based on
questionnaires and electro-physiological measures of sleep. Their purpose is to
provide an insight on how to more successfully predict which factors might lead
to accidents and to provide means for other method groups to focus on detecting
and preventing some key factors associated with driver drowsiness.
This way of measuring is known as Subjective Measuring , since testing subjects
were asked to describe their level of sleepiness, which is clearly a subjective
assessment of their perception of drowsiness.
Some of the best-known subjective tests of sleepiness are:

￿ Epworth Sleepiness Scale (ESS) [ 27 ]: an eight-item, self-report measure that

quantifies individuals' sleepiness by their tendency to fall asleep in static, non-
stressful situations: reading, watching television, sitting in a car at a traffic light.
On each of eight situations, subjects are rating their likeliness to doze off or