In conclusion, this study demonstrated that four eye symptoms
are reflective of driver sleepiness: ‘eye strain’; ‘difficulty
focusing’; ‘heavy eyelids’; and ‘difficulty keeping the eyes
open’. Two further symptoms (‘sore eyes’ and ‘tearful’) are
associated with driver sleepiness in simulators. Critically,
experiencing these eye-related symptoms is associated with
higher subjective sleepiness and impaired driving performance.
In particular, ‘heavy eyelids’ and ‘difficulty keeping
the eyes open’ are common when unintentional line crossings
occur. Including these eye symptoms in road safety
advice has potential for assisting drivers identify sleepiness