Studies suggest that driver fatigue is a factor in as many as 20% of all accidents and a quarter of all driver deaths[i]. In this second part of a two-part article, SCT’s Mario Pierobon focuses on driver vigilance, and specifically vigilance fluctuation, vigilance decrement, and the effects on information processing.

Driving as a Test of Vigilance

Inadequate vigilance and its direct consequences on safety is increasingly considered as major public health problems, especially in the field of transportation, according to Aurelie Campagne, Thierry Pebayle and Alain Muzet in a journal paper entitled ‘Correlation between driving errors and vigilance level: influence of the driver’s age’[ii] . “The fluctuation in the level of vigilance is a natural physiological phenomenon. Such a fluctuation could be due to a more or less important activation or arousal of cortical areas, leading the brain going from deep sleep to highly activated brain,” the researchers state. “Drowsiness represents one of the intermediate states in the transition from waking to sleeping and its further development can lead to sleepiness and then actual sleep to occur.”

According to Eike Schmidt, Michael Schrauf, Michael Simon, Martin Fritzsche, Axel Buchner and Wilhelm Kincses in a paper entitled “Drivers’ misjudgement of vigilance state during prolonged monotonous daytime driving”, driving can be considered as a vigilance task, especially when it is performed in a monotonous environment with little task demand[iii].

Factors that affect vigilance are of two types: exogenous and endogenous. This depends on whether they stem from within the organism or whether they are caused by characteristics of the task performed. The monotony of the road environment is therefore classified as an exogenous factor, while sleepiness is influenced by circadian and homeostatic variables, according to Schmidt at al.[iv].

Keeping Busy? 

“Long hours spent driving, referred to as the time-on-task effect, is known to produce fatigue and a deterioration of driving performance, although degradation can occur during the very early stages of a driving or vigilance task," say Thieffault & Bergeron.

Besides resource depletion caused by being actively engaged in a task, there are other signs that passive monitoring, monotony and passive fatigue can also induce vigilance decrement, according to Moritz Körber, Andrea Cingel, Markus Zimmermann and Klaus Bengler in a paper entitled ‘Vigilance Decrement and Passive Fatigue Caused by Monotony in Automated Driving’[v]. “Partially automated driving represents such a passive situation as the driver’s only task is to monitor the system,” they say.

According to an experiment conducted by Körber et al. with the aim of examining the effects of partial automated driving on participants' vigilance and passive fatigue in a driving simulator, the eye tracking results used in the study show that fatigue can occur even when there is no active engagement in a driving task, supporting the relevance of passive fatigue caused by automation. “Participants reported more engagement with their own thoughts at the end of the drive in comparison to the beginning, which can be seen as an indication for a lack of engagement in monitoring the automation. Nevertheless, no significant increase in reaction times occurred in the vigilance task,” the researchers state.

“We found no significant effects of time-on-task on the reaction times, but significant effects on eye tracking parameters (blink frequency, blink duration, pupil diameter) and increased mind wandering. The results show that fatigue can occur without active task engagement, but future studies have to clarify the consequences I terms of reactions to critical events,” affirm Körber et al.

Changing Stimuli

Lowering physiological activation can affect information processing by altering vigilance, observe Thieffault & Bergeron. “The ability to maintain sustained attention on a signal source over a prolonged period of time tends to decrease with activation and wakefulness,” they affirm. “However, the habituation process and the orienting response —a concept which can be related to dishabituation—are well-established phenomena in psychophysiological science.”[vi]

As to the functioning of habituation and orienting response, Thieffault & Bergeron explain that the first presentation of a stimulus, or the presence of a novel or incongruous stimulus, leads to increased arousal and a mobilization of attention. “After several repetitions of the stimulus, the response tends to decrease and disappear,” they state. “However, a change in stimulus leads to a reappearance of the response, with a corresponding increase of arousal and attention. Applying these general processes to the driving task implies that the presence of repeated stimuli on a monotonous environment could act on driver fatigue by decreasing arousal and one’s attention to the road. On the other hand, a change in stimulation, or the presence of a novel or incongruous stimuli, could lead to temporary increases of arousal and attention.”

More Automation?

Monitoring and warning drivers through technology is an approach to addressing fatigue and vigilance, with greater need now as vehicles become more automated. However, systems like internal cameras and steering wheel monitoring are not infallible. Recent research[vii] carried out by the AAA (American Automobile Association) in which a number of vehicles were tested in real world conditions, found that “driver monitoring systems are a good first step to preventing deadly crashes, but they are not fool proof.” Although camera systems fared better, even after issuing multiple warnings of inattentive driving, both systems failed to disable the semi-autonomous features and force the driver to take the wheel and pay attention the AAA found.

Driver employers can deploy vehicle safety monitoring technology which as well as drowsiness and distraction recognition (DDR) systems can include telematics systems, intelligent speed assist (ISA), and collision warning systems. But it is not only a matter of technology. Research sponsored by the UK Health and Safety Executive[viii] recommended “management and coaching feedback (for drivers) are a critical part of the system. Organisations should not rely solely on in-vehicle feedback” and “any system should be easy for drivers and anyone responsible for coaching their driving to use, access data from and interpret”.



[i] The Royal Society for the Prevention of Accidents “Driver Fatigue and Road Accidents Factsheet” July 2020 (
[ii] Aurelie Campagne, Thierry Pebayle, Alain Muzet, Correlation between driving errors and vigilance level: influence of the driver's age, Physiology & Behavior, Volume 80, Issue 4, 2004, Pages 515-524,
[iii] Eike A. Schmidt, Michael Schrauf, Michael Simon, Martin Fritzsche, Axel Buchner, Wilhelm E. Kincses, Drivers’ misjudgement of vigilance state during prolonged monotonous daytime driving, Accident Analysis & Prevention, Volume 41, Issue 5, 2009, Pages 1087-1093, (
[iv] Schmidt et al.
[v] Moritz Körber, Andrea Cingel, Markus Zimmermann, Klaus Bengler, Vigilance Decrement and Passive Fatigue Caused by Monotony in Automated Driving, Procedia Manufacturing, Volume 3, 2015, Pages 2403-2409,
[vi] Thieffault & Bergeron
[vii] AAA “Face It: Only One Type of Driver Monitoring System Works, But It’s Not Foolproof” January 2022 (
[viii] V Pyta, B Gupta, N Stuttard, N Kinnear, S Helman “Assisting the update of INDG382: Vehicle technologies” July 2020 (