Analysis of the driving behavior when the system safety level during automated driving is presented to drivers

Abstract

1. Motivation of study According to level 2 automated driving defined by SAE, drivers are legally responsible for driving and have the obligation to monitor the operation status of the system. The authors consider that presenting information on the system safety level to the driver will be effective in improving the task performance of driver to monitor the system status and at the same time reduce the workload of this monitoring behavior of driver. When the safety of the system is low, it is important to present such situation to the driver and prompts the driver to proactively monitor the operation status of the automated driving system. Even for level 3 automated driving where the driver is not obligated to monitor the system operation, this interface system is useful in presenting information on the system safety level to the driver. When it is difficult to avoid collision risk with just the system, the possibility of occurrence of a "Takeover request" (Gold et al., 2013)(Eriksson et al., 2017) for transferring the driving authority to the driver is high. For this reason, the authors consider that presenting information on the decrease in the system safety level to the driver is effective in maintaining a high level of "Readiness"(Kitazaki, 2018), which is the degree of preparation for driving by the driver. As shown in Figure 1, if the driving capability level (Capability (C)) of the driver meets the driving demand level (Task demands (D)) required by the environment, the driver can drive safely meeting the requirements of the environment (Fuller, 2005). During automated driving, if "C > D",it will be possible to maintain a certain constant value for the overall safety of the automated driving system and driver. Abstract In this study, it was analyzed how presenting information on the system safety level of automated driving system affects the driving behavior of driver, with the experiment using the driving simulator. During automated driving categorized to the level 2, we analyzed the driving preparation level of the drivers when presenting the system safety level on a display fixed on instrument panel. This driving preparation level of drivers was quantified, based on the gaze action and brake/gas pedal operation behavior of drivers, in a driving simulator investigation with 26 subjects' participation. As one of the experimental results, when system safety level was presented to drivers, the operation preparation level of the drivers increased instantly with the fall of the system safety level. We also quantified the effects by presenting system safety level in this driving simulator study. It was verified that the risk of the traffic accidents as Human-Machine system based on the state transition probabilistic model proposed by authors can be minimized when the system safety level was presented to the drivers. For instance, it was confirmed that the collision probability tended to reduce relatively by 37.9% with the indication of the system safety level.