Mercedes-Benz will put a new 'driver support' system called Attention Assist that can recognise driver fatigue into production next spring.

It said scientific studies indicate that around 25% of all serious accidents on motorways are caused by overtired drivers, an accident cause more significant than driving under the influence of alcohol.

"Studies have shown that the reaction times of drivers can be 50% longer after only four hours of non-stop driving. The risk of an accident is doubled after this length of time, and after six hours of driving it is no less than eight times as high," the automaker said.

Attention Assist monitors the driving behaviour of the driver, generating an individual driver profile which is constantly compared to a flow of sensor data. This continuous monitoring is important allows the system to recognise the driver's transition from alertness to drowsiness and warns him in good time.

In addition to the vehicle speed and linear/lateral acceleration, the system also registers steering wheel movements, indicator and pedal operation, plus a number of specific control operations and external influences such as side winds or uneven road surfaces.

Mercedes said monitoring the driver's steering behaviour has proved to be particularly relevant, as an overtired driver has difficulty in keeping the vehicle precisely on track and makes minor steering errors which are often quickly corrected in a characteristic manner.

Intensive tests involving more than 550 male and female drivers showed this effect commences during an early phase of the onset of fatigue - usually before the highly dangerous "one-second nap".

The heart of the system is an extremely sensitive sensor that enables the steering movements and their speed to be monitored precisely.

During the first few minutes of each journey, Attention Assist uses the data to compile an individual driver behaviour pattern which is constantly compared with the current steering behaviour and driving situation by the onboard electronic control unit. This enables the system to recognise the typical signs of over-tiredness and warn the driver accordingly. This is done by an acoustic signal and a display in the instrument cluster which says: "Attention Assist. Break!"

Toyota's top Lexus models are available with a system that monitors the driver's head position to detect inattention.

Safety equipment supplier TRW Automotive has developed an automotive equivalent of the commercial aircraft 'stick shaker' that vibrates the steering wheel if driver inattention causes the car to drift out of its lane.

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