The Usability of Graphical Symbols and Visual Aids Designed for Driving Automation Systems

Inconsistencies can be observed in the way vehicles equipped with driving automation features will inform drivers about a particular system’s state or capabilities and limitations: different graphical symbols are used across manufacturers to represent the same feature, while other graphical elements presented on the instrument panel can also differ in their designs. This situation could engender confusion among drivers, while some designs may be less informative and/or less usable than others, eventually being detrimental to driver safety. The objective throughout this project, therefore, was to demonstrate whether symbol confusion was an actual risk and whether the different symbol and interface designs could have measurable consequences on a vehicle’s usability. Ultimately, the goal was to determine which methodological approach could help design symbols and interface elements that would prevent or mitigate these putative consequences.

Firstly, two studies were conducted with a user-centred design (UCD) and participatory design approach to ① investigate drivers’ mental models of the adaptive cruise control (ACC) and lane centring control (LCC) systems and design symbols for these two systems, and then, to ② research which symbols would be the most recognised by drivers contextually and alongside other symbols present in vehicles. Secondly, two driving simulator studies were conducted to ③ compare the usability of different graphical elements shown on the instrument panel for ACC, including different designs of the same symbol, and finally, ④ compare two sets of symbols for ACC, LCC, lane departure prevention (LDP), and the automated lane-keeping system (ALKS), in terms of driver preference, but also on how much confusion and how many errors would occur while drivers were using either set.

Overall, the results suggest that some existing symbols (notably the standard ones) lack information about which actions are automated by a system, or how the visual representation of the environment relates to the actions performed by the system. In scientific jargon, drivers overall preferred, recognised, and committed fewer errors with symbols that depicted drivers’ affordances and the signifiers that the vehicle was using in place of the driver. Through this project, it was observed that: indeed, symbols can confuse drivers and contribute to use errors of the automated driving features; that interface designs could impact the usability of vehicles differently; and finally, that a combination of UCD and participatory design can help design better symbols. In the case of symbols for driving automation systems, designers should consider the context of use of the system and which affordances/signifiers should be represented on the symbol.