Experiences with Advanced Cruise Control in traffic; a limited experiment. Advanced Cruise Control (ACC) is an ordinary cruise control in which the desired speed is installed manually, but in which the headway time to the vehicle in front is also taken into account. If the headway time becomes less than the installed critical threshold value, the system brakes the vehicle gradually. If the vehicle in front is no longer there, or the headway time is greater than the threshold value, the installed speed is again resumed. If the vehicle in front approaches at too high a speed, the system also brakes. This braking can occur by reducing speed, changing to a lower gear (in automatic gearboxes), or using the brakes. An ACC system is meant for use on rural roads during quiet periods. The system is not meant to avoid collisions during critical circumstances; it is nót an anti-collision system. While using an ACC system, the driver keeps the final responsibility; he/she can disengage the system at any time. Much research has been done in the use of ACC and any road safety effects, for example using computer simulations, with subjects in driving simulators, and in some experiments on a driving range or on the road. However, these experiments were all carried out with an experimental ACC. As far as we know, no research in the Netherlands or elsewhere in Europe has been done with a factory-installed ACC in real traffic. For this reason an explorative study was done with ACC in a Nissan Primera, that was willingly supplied by NISSAN Netherlands Ltd. The purpose was to get an impression of the first experiences with ACC, and to compare them with what was known from scientific reports. This impression can help indicate necessary supplementary research. Ten people participated in the experiment, and these were recruited from and via SWOV personnel. The test journeys lasted between one and two hours. After the test journey, a questionnaire was completed. The questions included were derived from the reports and previous test journeys. Because of the select sample and its limited size, the results only have an indicative character. In general, the ACC system was judged positively and it enjoyed support. The guidebook was judged positively, as was the ease of the switches. The position of the display, on the right-hand side above the dashboard, was found to be less positive; it distracted the attention. The legibility was also found not to be so good. Preference was given to a short headway time. The majority were of the opinion that ACC did not decrease the attention, but did ease the driving task. When rapidly approaching a slowly moving vehicle in front, the ACC system braked rather late and hard; the driver tends to brake earlier. When overtaking, the acceleration of the ACC system was rather sluggish, whereby there was the tendency to accelerate self. We recommend supplying a cd-rom or DVD with the guidebook, making it possible to conduct a test drive interactively behind a computer. A better position for the display is where, in most cars, the speedometer is situated. The symbols on the display should be larger and clearer. If the driver himself brakes and does not wait for the system, the brake system of ACC can serve as a secondary one. This brake system starts to work if the driver has not yet done so. With this, it is expected that safety will be promoted. When overtaking, the driver should accelerate to avoid unnecessarily hindering vehicles behind if the ACC acceleration is insufficient. Finally, we recommended that supplementary research be conducted in which ACC systems of various car manufacturers are tested during a longer period and with more participants.
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