In-field evaluation of the effects of Continuous Driver Support on driver behaviour András Várhelyi Anna Persson Clemens Kaufmann

The Continuous Support system The system provides the driver with the following warnings: When the actual speed is above the speed limit, the display shows the speed limit icon. When approaching a curve at a too high speed: - as a pre-warning, the display shows a yellow curve icon; - as an imminent warning, the display shows a red curve icon, an alarm sound is activated and the safety belt is tensioned. In a situation with risk for a forward collision: - as a pre-warning, the display shows a yellow obstacle icon; - as an imminent warning, the display shows a red obstacle icon, an alarm sound is activated and the safety belt is tensioned. In a situation with a vehicle in the blind spot: - as a pre-warning, the display shows a yellow blind-spot obstacle icon; - as an imminent warning, the display shows a red blind-spot obstacle icon.

53 km of varying driving conditions, motorway and rural-road sections, 40 to 45 minutes to complete. Test route

Study design 24 test persons (employees of CRF) Each driver drove 2 times (once with- and once without the system, in alternating order) Data collection: - Log data - Behaviour observation - Interviews Total Male7613 Female9211 Total16824

vehicle status, system activities and driver-generated events Number of generated warnings for - too high speed, - risk for forward collision, - risk for side collision. Alarm length (time spent in alarm phase). Logged data

Two observers in the car one observed standardised variables (interactions, lane changes, etc.), the other observer carried out ‘‘free observations’’ of conflicts, communication and special events. Behaviour observation (Wiener fahrprobe)

Experienced effects of the system Subjective workload (Raw Task Load indeX - RTLX) Usefulness and satisfaction Willingness to have and pay General feelings about using the system, possible problems, possible improvements. Interviews

Results Effects: + Curve speed warnings gave the expected effect + Better speed adaptation to the speed limits and situations + Less dangerous lane changes with the system active -Slightly more late adaptations of speed before intersections and obstacles Opinions: Useful Blind spot warning especially useful in the overtaking process Appreciated not giving information all the time

What differences did you notice while using this system compared to driving without the system?

Rating of the items of “usefulness” and “satisfaction” Useless Good Superfluous Worthless Sleep inducing Unpleasant Annoying Likable Desirable

Usefulness – Satisfaction rating of interactIVe functions

Subjective workload (mean Raw Task Load indeX -RTLX) Without system active With system active Sign. of difference Mental activity Physical activity Time pressure Own performance Effort Frustrated

Willingness to pay for interactIVe functions The test persons are willing to pay more for functions that intervene than for functions which only warn

Recommendations The system should not warn the driver too often, and not too late. In an emergency situation, visual information should be given and be shown for enough time, so the driver finds out the reason for the haptic or acoustic warning. The visual display for the forward collision warning should be put as high as possible. An additional haptic warning for the blind spot warning would be preferable Safety belt tensioning should not be used for both speed and forward collision warning. Some training would be useful before using the system, at least to get to know the different warning signals not to be surprised when they come the first time. Introduction by the car seller or a demo-mode should be available, so that the warnings can be shown while the vehicle stands still.

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