1. Fit-for-duty test for estimation of
drivers' sleepiness level:
Eye movements improve the Sleep/Wake predictor
Christer Ahlstrom1, Marcus Nyström2, Kenneth Holmqvist2, Carina Fors1, David Sandberg1, Anna
Anund1, Göran Kecklund3, Torbjörn Åkerstedt3
1
Swedish National Road and Transport Research Institute (VTI), Linköping, Sweden
2
Humanities Lab, Lund University, Lund, Sweden
3
Stress Research Institute, Stockholm University, Stockholm, Sweden
Abstract
Driver sleepiness contributes to a considerable proportion of road accidents, and a fit-for-duty test able
to measure a driver’s sleepiness level might improve traffic safety. The aim of this study was to
develop a fit-for-duty test based on eye movement measurements and on the sleep/wake predictor
model (SWP). Twenty-four drivers participated in the study which took place partly in the laboratory,
where the fit-for-duty data were acquired, and partly on the road, where the drivers fitness to drive was
assessed. A series of four measurements were conducted over a 24-hour period during different stages
of sleepiness. Two separate analyses were performed; a variance analysis and a feature selection
followed by classification analysis. In the first analysis it was found that the SWP and several eye
movement features involving anti-saccades, pro-saccades, smooth pursuit, pupillometry and fixation
stability varied significantly with different stages of sleep deprivation. In the second analysis, a feature
set was determined based on floating forward selection. The correlation coefficient between a linear
combination of the acquired features and subjective sleepiness (Karolinska sleepiness scale, KSS) was
found to be R=0.73 and the correct classification rate of drivers who reached high levels of sleepiness
(KSS≥8) in the subsequent driving session was 82.4 % (sensitivity = 80.0 %, specificity = 84.2 % and
AUC = 0.86). Future improvements of a fit-for-duty test should focus on how to account for individual
differences and situational/contextual factors in the test.