Analogue versus digital speedometer: effects on distraction and usability for truck driving

European Conference on Human Centred Design for Intelligent Transport Systems, LOUGHBOROUGH, ROYAUME-UNI, 30-/06/2016 - 01/07/2016; Speed is one of the essential information needed to perform correctly the primary driving task. While driving a truck, a misjudgement of speed can lead to rollover in a bend (particularly for concrete mixer trucks), jackknifing at braking, or swinging out on slippery roads [1]. In addition to visual, auditory and vestibular cues, the speedometer on the dashboard provides a more accurate speed value to the driver. The design of the speedometer is critical for road safety because it generates a very high number of glances out of the road that could overlap a time-critical event. Two main types of speedometers are currently proposed in the truck industry: analogue and digital speedometers. In the human factors literature, some studies investigated the effects of both speedometers on human behaviour. Results are mostly equivocal but it seems that the more appropriate mean of presenting the speed information to the driver depends on the task performed. A digital speedometer would be more appropriate for an absolute reading of the speed value [2]-[5], and for a relative reading task (i.e. compare to a target speed) [2], [6]. An analogue speedometer would be better for reading a dynamic speed change [6]-[8]. Moreover, the existing literature does not allow concluding whether an analogue or digital format is better for truck speedometer design. First, most studies have been conducted on cars. Compared to car driving, truck's driver eye position is higher (thus, far from the dashboard) and the difference in vehicle speed variation (due to vehicle weight) could impact speed management and control. Second, existing studies have been obtained with conventional mechanical and physical supports. Advancements in display technologies (i.e. with liquid crystal display - LCD - screens as instrument cluster) make it interesting to update the results for a more contemporary vision. This study aimed at comparing an analogue and a digital speedometer in terms of usability and distraction in simulated truck's driving on a LCD screen. 18 trucks drivers were equipped with an eye-tracker and were required to drive on a driving simulator. Results showed that reading the value of the speed (i.e. absolute reading) was faster and less distracting, and the reported cognitive effort was lower with the digital speedometer. Similarly, the digital speedometer was more efficient for a relative reading task (i.e. say if the speed value was under or over 50km/h). On the contrary, detecting if the speed was decreasing or increasing (i.e. dynamic change reading) was faster and less distracting with the analogue speedometer. Both speedometers were perceived as usable by drivers, but the global preference went to the digital speedometer. The existing results in the literature have therefore been replicated and extended to truck drivers on a LCD instrument cluster. Future researches can then rely on these results to investigate new speedometer representations that would be efficient for the three reading types.