Daimler HighTechReport: The Fascination of Technology - Issue 02/2008 - PART VIII


Stuttgart, Nov 25, 2008

Attention Assist: Don’t Fall Asleep!

Assistance system can provide early warning of detected fatigue

Fatigue stage (algorithm)

Ten heartbeats…

December 2, 2009: After a long work day, Uwe Miller is on his way home. The sales representative set out at 7:00 a.m. and visited five customers in northern Germany. It’s now 10:00 p.m. and the daily mileage counter shows he’s traveled 578 kilometers. Miller is still a little over 100 kilometers from home.

…on the highway

After a dinner with his last customer in “Y city,” Miller decided to take the autobahn for his return journey, even though it is somewhat longer than taking the state road. Although the day has been successful, it was also strenuous, so Miller is feeling tired and leans back in his seat.

A deceptive calm…

Miller is one of the very few drivers on the road at this time of night. He has both of his hands on the steering wheel and is staring ahead at the road. He isn’t really registering what he sees, however, because in his thoughts he is already back home.

…before the alarm goes off

Miller’s attention is suddenly jerked back to the road by an alarm. At the same time, a coffee cup symbol lights up on his car’s instrument cluster as do the words “Attention Assist Pause.”

Warning in good time…

Miller realizes he wasn’t focusing on the road in the few minutes prior to the point when the alarm went off. That explains why he had swerved over to the right shoulder and unconsciously corrected the movement with a quick steering maneuver. Miller would not have been aware of this if the assistance system hadn’t warned him of the fact. Miller’s pulse races merely from the thought of what could have happened.

…reduces the risk of accidents

Miller is glad that his car warned him in time of the danger, aware that the next lapse in attention might have caused him to swerve completely out of the lane and slam into the guard rail. With this in mind, he decides to get off the autobahn at the next rest stop so that he can walk around a bit and get some fresh air. He might drink a coffee as well — it’s better to get back home ten minutes later than to cause an accident.

Fatigue stage below the warning threshold

Fatigue stage above the warning threshold

Sleeping can be fatal - especially if it occurs at the wheel of a car. Microsleep is a common cause of traffic accidents. Although some of them are minor, most are quite serious. Here are a few examples taken from police reports in three German dailies:
Biberach Excerpt from the police report of March 31, 2008: “The accident that killed a six-year old boy near Dürmentingen at midday on Sunday was caused by driver fatigue. The 77-year-old man responsible for the accident … had been driving for a total of six hours before the collision occurred. The tire marks at the scene of the accident show that the driver had attempted to steer his car from the right curb back to the road shortly before the collision occurred.”

Düsseldorf Excerpt from the police report of January 2, 2008: “Mettmann - An extremely fatigued 23-year-old woman caused a traffic accident on Haydnstrasse late Tuesday evening that resulted in extensive damage. … While taking a gentle curve to the left, the driver collided with a parked Audi A4 Avant. In her statement, the young woman said she was so exhausted that her eyes had just closed while she was driving.”

Stuttgart Excerpt from the police report of June 10, 2008: “Leonberg - The front-seat passenger in the vehicle that crashed on Autobahn A 8 near Leonberg (district of Böblingen) on Monday has died of his injuries, the police announced on Tuesday. The 37-year-old driver had swerved out of his lane and collided with a semi-trailer, probably as a result of fatigue.”

Underestimating the degree of fatigue These three examples show how microsleep can suddenly turn into a potentially fatal nightmare. Despite this fact, microsleep is generally underestimated. According to official statistics in Germany, around one percent of all serious traffic accidents are caused by “excessive fatigue.” However, this figure has little relation to the reality on the roads, where it is often impossible to confirm that fatigue was the cause of an accident. In fact, many studies show that the actual figure is far higher. A survey conducted in Austria, for example, revealed that 33 percent of fatal traffic accidents in the country were caused by fatigue. Accident researchers estimate a rate of 24 percent in Germany, and studies have come to similar conclusions in the U.S. and Canada.

According to the surveys, fatigue probably surpasses drunk driving when it comes to causing serious traffic accidents. Staying awake for 17 hours has the same effect on the body as a blood alcohol content of 0.5 per mille. “Accidents due to fatigue are a serious problem,” says Jörg Breuer, Head of Active Safety at Vehicle Development Mercedes-Benz Cars. “The probability of being killed in an accident resulting from fatigue is more than 2.5 times as great as for any other cause of accidents.”
In addition to sleep deficit, monotony is the most common cause of sleeping at the wheel, since many people find long-distance driving on straight roads extremely boring. Alertness therefore diminishes rapidly in such situations, leading to a rapid increase in the risk of falling asleep and causing an accident.

Also tired during the daytime “Around two-thirds of all accidents caused by fatigue occur when it’s dark, and half of these accidents occur when traffic density is low,” says Breuer. Conversely, this means one-third of all accidents caused by fatigue occur during the daytime.

In testing hundreds of motorists, Daimler experts have learned that many drivers fail to accurately judge their state of fatigue, or they don’t notice it in time, an even more commonplace phenomenon. “Fatigue does not generally set in suddenly; it builds up over a certain period of time,” explains Breuer’s colleague Elisabeth Hentschel. “Reactions and powers of perception deteriorate continuously - and to such a pronounced degree that the driver’s ability to take the correct action may be compromised even in the early stages of fatigue.”

An entirely new approach In 2002, Group Research launched a fatigue recognition project, which was transferred to the development units two years later. The result of this work is an innovative assistance system known as Attention Assist. It can detect fatigue in its initial stages and warn the driver before any dangerous microsleep phases occur. Mercedes-Benz will begin series production of Attention Assist next year. The Daimler engineers decided to take a totally new approach in the design of the new assistance system. Unlike other systems that visually monitor things such as the frequency with which the driver opens and closes his or her eyes or how well the vehicle stays in its lane, the new system developed by Mercedes-Benz evaluates a number of different indicators. Breuer describes some of the details: “The observation of steering behavior is particularly revealing, because a tired driver has difficulty staying precisely in the lane. He or she makes small steering mistakes that are often quickly corrected in a characteristic manner. Extensive tests that our engineers at Mercedes have conducted with more than 550 drivers have shown that this effect already appears in an early stage of fatigue, generally before the dangerous microsleep phase begins.“

Recognizing concentration lapses Attention Assist can recognize these indicators, which are lapses in concentration that result in characteristic steering corrections. If a driver’s steering behavior noticeably changes and there are other indications of fatigue, the electronic assistance system emits an alarm in good time. Besides the alarm sound, the system also warns the driver visually by means of an illuminated coffee cup symbol on the instrument cluster, notifying the motorist to take a break. The innovative Attention Assist system continuously monitors the driver’s typical behavior patterns and uses this data to create an individual driver profile that serves as the basis for detecting fatigue. Breuer’s colleague Uwe Petersen describes the challenges the development engineers had to overcome to make this possible: “Our main task was to detect the smooth transition from a wakeful state to one of fatigue, in other words from a state of high concentration to one of a marked attention deficit.”

Small sensor Attention Assist registers the driver’s individual steering behavior with the help of a steering angle sensor that measures movements of the steering wheel with great precision. An alert driver continuously makes small, imperceptible corrections that create a characteristic pattern when recorded as a signal curve. The system notices if a driver is very tired because he or she hardly moves the steering wheel for a short time before suddenly taking corrective action.

Attention Assist is a fast learner, because “it doesn’t need much time to determine a motorist’s personal driving and steering profile,” says project manager Werner Bernzen. If the driver’s behavior significantly deviates from the stored empirical values, the system can then determine whether or not there are any indications of the onset of fatigue. “However, whether or not a driver is warned depends on the time of day, the motorist’s driving style, and how long he or she has been driving,” adds Elisabeth Hentschel. “What’s more, the system also takes into account the type of driver it is dealing with. Some drivers steer smoothly and very calmly, while others turn the steering wheel in a comparatively abrupt fashion.”

Studying external influences In addition to analyzing the motorist’s personal driving and steering profile, the system records numerous vehicle-related values including its current speed and its longitudinal and transverse acceleration. Other factors taken into account include activation of turn signal lights, depressing the accelerator or brake pedals, and operation of the radio, telephone, or navigation system. Last but not least, ­Attention Assist also factors in external influences such as side winds or bumps in the road that might affect steering behavior.

Development of this unique assistance system began with a series of tests in the driving simulator in Berlin. The engineers then took the results of these tests and compared them with experiences recorded during daytime and nighttime drives on highways and country roads all over the world. To date, more than 550 test subjects have tested Attention Assist and assessed its reliability, covering more than 750,000 kilometers in the process.

Accident prevention “Attention Assist is the first assistance system that continuously monitors the vehicle and driver, who is warned if the system determines that typical behavior patterns and other indicators show there is danger of fatigue or an accident,” says Breuer. “With this performance, the system can make an important contribution to accident prevention.”

“Driver fatigue probably causes more serious accidents than drunk driving.”

Jörg Breuer, Head of Active Safety Mercedes-Benz Cars
“We extensively tested Attention Assist in the driving simulator and in practice, with 550 test subjects.”

Uwe Petersen, Active Safety Mercedes-Benz Cars
Driving fatigue typically progresses through four phases. Starting in 2009, the future Attention Assist will be able to warn drivers when they pass from the first to the second phase, long before microsleep sets in.


In developing Attention Assist, Daimler investigated various methods of fatigue recognition and measured brain waves. Additional information is available at HTR online:
A photo gallery on the system’s development and testing
Information: “Safe driving with assistants” - The benefits of ESP and Brake Assist (BAS)
Information: “A state between sleeping and dreaming” - The biological causes of fatigue


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