Prolonged driving is accompanied by a decreased motivation to continue driving and reduced accuracy of lateral and longitudinal vehicle control . To a certain extent motivation, i.e. the investment of extra mental effort, can compensate for the performance-decreasing effects of prolonged driving. However, sustained effort may not be enough because the ability to monitor the efficiency of one’s own performance may deteriorate as well as a result of fatigue . On the basis of experimental simulator studies, Matthews & Desmond  suggest that task-induced driver fatigue reduces awareness of performance impairment. Moreover, task-fatigued drivers appear to have difficulty mobilizing sufficient task-directed effort (i.e. keeping enough attention on the task and responding to signals). This is especially the case when task demands are low. Theoretically, in a fatigued state, performance goals become de-activated, perhaps due to competition from comfort-seeking goals, and thus the drivers loses awareness of performance deterioration. The same authors link sleep-related fatigue with reduced motivation or inability to mobilise compensatory effort following detection of impairment .
Under normal circumstances drivers are likely to increase their safety margins when they become fatigued and performance deteriorates . When performance is starting to deteriorate, taking (frequent) breaks may cause recovery of normal performance. A French on-road study showed that rested, non-professional driver can drive 1000 km from 9 am to 7 pm, with three 15 minutes breaks and one 30 minute break, without noticeable performance decrement . The study demonstrates that fatigue generated by extensive driving has a limited impact on driving skills in normally rested drivers.