Fit-for-duty test for estimation of drivers’ sleepiness level: Eye movements improve the sleep/wake predictor Christer Ahlstrom a,⇑ , Marcus Nyström b , Kenneth Holmqvist b , Carina Fors a , David Sandberg a , Anna Anund a , Göran Kecklund c , Torbjörn Åkerstedt c a Swedish National Road and Transport Research Institute (VTI), Linköping, Sweden b Humanities Lab, Lund University, Lund, Sweden c Stress Research Institute, Stockholm University, Stockholm, Sweden article info Article history: Received 22 December 2011 Received in revised form 11 June 2012 Accepted 24 July 2012 Keywords: Fit-for-duty test Eye movements Driver sleepiness Field study 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, which predicts the sleepiness level) and evaluate the ability to predict severe sleepiness during real road driving. Twenty-four drivers partic- ipated 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 differ- ent 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 P 8) in the subsequent driving session was 82.4% (sensitivity = 80.0%, specific- ity = 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. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Driver sleepiness contributes to a considerable proportion of road accidents (NTSB, 1999; Åkerstedt, 2000). In the UK, the proportion of sleep related vehicle accidents has been estimated to about 10–20%, where the higher percentage refers to motorway driving (Horne and Reyner, 1995; Maycock, 1997). In France, about 10% of single vehicle accidents are believed to be related to sleepiness (Philip et al., 2001) and in Finland, about 15% of fatal accidents caused by nonprofessional drivers are related to sleep or sleepiness (Radun and Summala, 2004). A fit-for-duty test, able to assess and predict driver sleepiness, 0968-090X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.trc.2012.07.008 ⇑ Corresponding author. Address: VTI, SE-581 95 Linköping, Sweden. Tel.: +46 13 20 40 09; fax: +46 13 14 14 36. E-mail address: christer.ahlstrom@vti.se (C. Ahlstrom). Transportation Research Part C 26 (2013) 20–32 Contents lists available at SciVerse ScienceDirect Transportation Research Part C journal homepage: www.elsevier.com/locate/trc