Fit‐for‐duty test for estimation of drivers’ sleepiness level: Eye movements improve the sleep/wake predictor

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, which predicts the sleepiness level) and evaluate the ability to predict severe sleepiness during real road driving. Twenty‐four drivers participated in an experimental study which took place partly in the laboratory, where the fit‐for‐duty data were acquired, and partly on the road, where the drivers sleepiness was assessed. A series of four measurements were conducted over a 24‐h 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, and whether it is possible to maintain high sensitive/specificity with a shorter test that can be used in a real‐life environment, e.g. on professional drivers.