FAMILIARIZATION WITH CRITICAL SITUATIONS WHEN USING A FORWARD COLLISION WARNING : EFFECTS ON DRIVER-SYSTEM INTERACTIONS

A Forward Collision Warning (FCW) could avoid a large number of rear-end collisions by informing distracted drivers of the danger. However, the FCW generates false and nuisance alarms, or cannot indicate some dangers. These critical situations could lead to unsuitable reactions and diminish acceptance if drivers have a poor understanding of the system’s operations. This research aims at evaluating the benefit of familiarization with these situations. In a simulator study we compared drivers’ behavior and their acceptance according to whether they used the system in a familiarization session. Results show that familiarization led to better understanding of the FCW, thus making driver/system interactions more effective and safer. However, familiarization had no effect on drivers’ acceptance and even decreased their confidence in self-performance. We addressed practical applications for the deployment and rollout of FCW systems. Rear-end collisions account for 25% of all road accidents [1]. They are the most frequent crash type which constitutes 5% of all fatalities and 53% of all injuries on U.S. highways [2]. In-depth analysis shows that drivers’ distraction is the main contributing factor, especially when the drivers are involved in a secondary task [3]. The Forward Collision Warning (FCW) is likely to reduce the number and the severity of these collisions by informing distracted drivers of the critical decrease in the distance from the lead vehicle. However, drivers do not accept the FCW easily. It has been shown that acceptance determines the way which drivers interact with automation (e.g. [4]). For example, the operators do not accept and “disuse” a system that is not reliable, annoying or disturbing [5, 6]. Ideally, the FCW should inform the drivers that he/she must react to avoid a collision. But in fact, the system sometimes fails to provide precise information: for example, the FCW can generate false alarms – i.e. a signal when the danger is absent – when detecting stationary objects located outside the road. False alarms thus strongly decrease the system’s reliability and the drivers’ trust [7, 8]. On the other hand, the FCW can miss some risk of rear-end collision when the target is out of the beam range (e.g. at a hill crest or in sharp turns). These omissions have even more negative impact than false alarms [9]. Moreover, most of the time the FCW indicates situations where the drivers would be careful (e.g. when following closely). But less frequently, the system also indicates situations where the drivers would brake sharply (e.g. when the lead Human Centred Design for Intelligent Transport Systems 38 vehicle suddenly stops). Consequently, drivers’ response must be adjusted according to the situation [10]. If drivers have a poor comprehension of the FCW’s operation, then they may react in an unsuitable way in response to false alarms or when they follow too closely, whereas they may react late when a danger is not indicated or when they face an imminent danger. Drivers’ comprehension is thus a key to determine when and how they have to react to the situation. Studies on drivercentered design – the adaptation of the driver/machine system to the operator, the task, and the automation’s characteristics (e.g. [11]) – succeeded in clarifying the meaning of alarms by modulating their format and/or their timing in accordance with the situations or the drivers’ individual differences (e.g. [12, 13, 14, 15, 16]). However, most of the researchers conclude that these adaptations failed to significantly improve drivers’ acceptance because the alarms still remain too frequent. In fact, there are many occasions where close following is not dangerous. This is typically the case when the lead vehicle slows down in order to change direction or when the driver prepares to overtake another vehicle (e.g. [17]). Then, the FCW triggers nuisance alarms which are often perceived as false alarms by the drivers [10]. A solution could consist of improving the comprehension of the FCW’s functioning. Once the drivers understand when and why an alarm is issued, drivers could be more tolerant towards the system. Studies in Field Operational Tests (FOT) provide information on the way to instruct drivers. Generally, they received oral or written descriptions of the system’s purpose, its operation, and the human/machine interface before a practice training (e.g. [14, 17, 19, 20]). Especially, [20] were particularly attentive to the drivers’ training, comprehension, and knowledge refreshing. Nevertheless, the FCW was regarded as unacceptable because of false or nuisance alarms. In driving simulator situations, familiarization with the FCW and details about its operation change greatly amongst studies (see [9] and [18] for example). The literature on the impact of drivers’ comprehension is poor. To the best of our knowledge, system comprehension has never been used as an independent variable. The ideal way to instruct drivers is not determined yet. However, FOT suggested that drivers appeared to “probe” the system’s function in extreme conditions to better understand capabilities and limitations [14, 19]. Then, confronting the drivers with critical situations could be effective to improve the knowledge of the FCW. To create these situations on a driving simulator would be convenient and safer. The present research aims at evaluating changes in the drivers’ behavior and their acceptance of the system according to their familiarization with the FCW on a simulator. We hypothesize that using the system in critical situations (i.e. when alarms are useless or absent) increases the acceptance and the effectiveness of the driver/system interactions. In addition, we suggest that this knowledge is more effective when drivers experience the situations rather than read a written description. To avoid possible bias related to the individual differences, we neutralized factors which would influence the drivers’ acceptance: age, sensation seeking, and preferential headway (see [12, 18]). Effects of ITS on drivers’ behaviour and interaction with the systems