Volvo believes they are the first truck manufacturer in Europe to develop a system that uses a camera to monitor the vehicle's course in relation to the road markings. Using ‘Driver Alert Support’, if a driving pattern is perceived as irregular, the driver is alerted by an audible signal and a text message in the driver information display. If the irregular pattern continues, the driver is cautioned to stop and take a break.
Volvo video -
http://www.youtube.com/watch?v=G2vWzuEu5UE
Is there not another in truck camera to eye scanning system in the pipeline, the drivers eye movements are scanned for the first few miles and after that if your eye movements are irregular and slow down it triggers an alarm.