Task load of professional drivers during level 2 and 3 automated driving

As level 2 automated driving systems (SAE partial automation) become more elaborate, the similarity to a level 3 system (SAE conditional automation), from a driver’s perspective, is gradually increasing. We examined differences in driver behaviour concerning level 2 and 3 automation in a driving simulator experiment with 31 professional truck drivers. All drivers received specific instructions concerning differences in the driver’s role in both automation levels. Despite this, drivers had difficulties in adapting their behaviour to the different demands of level 2 vs. level 3 driving. An analysis of driver reactions shows potentially critical lapses in attention during level 2 drives, when drivers were performing an engaging non-driving related task while driving. A comparison of drivers’ gaze distributions suggests that these lapses are likely due to a de-prioritisation of on-road glances during task performance. These results highlight the difficulties that may accompany improvements of level 2 automation performance and underline the need for measures to assist drivers in adapting their behaviour accordingly. Introduction and previous work Advancing sensor technology and signal processing methods lead to a gradual improvement of automation performance in automated level 2 (SAE 2016) vehicles, resulting in fewer driving mistakes that vindicate the driver's supervisory role. From a layman's perspective, well-functioning level 2 systems more and more seem like level 3 systems (Campbell et al., 2018). These systems seemingly need no supervision, despite the fact that the driver is still considered a crucial safety factor by its designers (SAE 2016). In both partial (SAE level 2) and conditional automation (SAE level 3) the driver’s main task can be described in terms of a vigilance task (Davies & Parasuraman, 1982): In partial automation drivers monitor longitudinal and lateral control to detect and respond to silent automation failures. In conditional and higher automation modes, drivers detect and respond to requests to intervene, which are issued by the automated system when it approaches a system boundary. System designers may adjust the saliency of requests to intervene such that the signal detection task in level 3 42 Bieg, Daniilidou, Michel, & Sprung automation and higher becomes relatively easy. For example, relevant design guidelines mandate the use of multimodal warnings and offer advice on colour, symbolism, and warning tones or messages (e.g., Campbell et al., 2018). No such control over signal saliency is available for level 2 driving: silent failures may take on the form of lane drifts or non-reactions (NTSB 2017). Previous work suggests that drivers may find it difficult to appreciate the demands of a (well-functioning) partially automated vehicle. For example, Omae et al. (2005) and Llaneras et al. (2013) found that drivers were more likely to engage in non-driving related tasks that restricted their monitoring ability such as interacting with a handheld electronic device. Such results may potentially be explained by assuming that drivers lacked exact information about the automated system’s capabilities or their monitoring duties and may be combated by appropriate instructions (Campbell et al., 2018). The presented work directly compares the behaviour of instructed, professional truck drivers to examine whether the drivers are able to adjust to the differential demands of level 2 and level 3 automation. Materials and methods The study was conducted in MAN’s fixed-base, high-fidelity driving simulator with professional truck drivers.