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2020年11月 8日 (日)

Take-over evaluation by driving simulator (5)

In our laboratory, we have conducted several experiments on the behavior of the driver during the emergent take-over using a driving simulator. Here are some of the highlights.

The first consideration was whether the emergent take-over would be feasible. The first thing we had to think about was how many seconds before we could issue a take-over request. The take-over request occurs when an automated driving sensor detects an obstacle that cannot be handled by the automated driving system alone during automated driving at level 2, issues the take-over request to the driver, and immediately cancels the automated driving. Take-over requests are issued with a high frequency beep sound that is clearly distinguisable to the driver. If the detection distance of the automated driving sensor is 200 m and the obstacle is a stationary object, the vehicle speed is 27.8 m/s (100km/h), so 200 / 27.8 ≈ 7 seconds, and the take-over request can be issued at the point of 7 seconds to the obstacle. A 140 meter sensor can detect 5 seconds before, while a 100 meter sensor can detect 3.6 seconds before.

Based on the above settings, an experiment was conducted to determine whether take-over requests can be made with 3 types of TTC: 7 seconds, 5 seconds, and 3.6 seconds. The position of the obstacle causing the take-over request in this experiment was changed every time the experiment was performed so that the position was not expected by the driver. The test was conducted on a highway with two lanes, a driving lane and a passing lane.

An experimeter told the driver that it was automated driving until the take-over request was beeped, and told a driver to determine the reason for the request and act accordingly. The experimenter did not mention changing a lane with the steering wheel or slowing down with the brake pedal. The driver was also asked for one of the following six tasks until the take-over request was issued.

i) Place both hands on the steering wheel and watch ahead. The foot position is free.
ii) Release both hands from the steering wheel and the line of sight was free. The foot position is free.
iii) Place both hands on the steering wheel and watch the video on the navigation screen.
iv) Release both hands from the steering wheel and watch the video on the navigation screen.
v) Put one hand on the steering wheel and perform an additional task.
vi) Release both hands from the steering wheel and perform the additional task.

The navigation screen was installed at the lower part of the center of the instrument panel, and the forward view could not be seen when the navigation screen was closely observed. The additional task is a task of inputting many four-digit numbers presented next to the navigation screen.

Before we get to the experimental results, let's assume the response of the driver from the take-over request to the take-over. However, it is more important to estimate the process by which the results are obtained and compare them with the actual results than to obtain the experimental results. When the take-over request is issued, if the driver is not looking ahead, it is likely that the driver will immediately turn his/her face forward and turn his/her attention forward. The driver will try to understand the situation to find out why the take-over request was issued.

Then, once the driver understand the situation, he/she should choose the action appropriate for the situation and move on to the action such as steering or braking. When such the action is carried out, the take-over of the driving task is completed, and the vehicle enters a so-called manual driving loop in the driving feedback loop. In the case of automated driving, the driver is not involved in the operation at all, so it can be said that the vehicle is outside the driving which is out of the feedback loop. That is, after the take-over request, the driver can be thought of as returning to manual driving operation, understanding the situation, and starting the manual driving operation to complete the driving feedback loop by manual operation.

If the above actions were completed within TTC seconds, the take-over would have been established.

 

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