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2020年11月 9日 (月)

Take-over evaluation by driving simulator (6)

A total of 14 collaborators randomly selected subtasks i) through vi) for each experiment in the case of TTC of 7 seconds and 5 seconds, and the take-over was confirmed for all experiments. ​The way to handle obstacles was basically avoided by steering. As expected, the behavior of the collaborators from the time of the take-over request was as follows: they immediately looked ahead from the direction they were looking at in order to perform the subtask; at the same time, if they released the steering wheel, they grasped the steering wheel with both hands; they understood the situation and shifted to the avoidance operation.

All 14 persons avoided obstacles by steering without stopping, but the pedal operation was different by the driver. ​When a take-over request was issued, the brake was not applied and only the accelerator was turned off, so 8 out of 14 persons operated the steering wheel while depressing the accelerator pedal and maintaining the vehicle speed. ​On the other hand, 6 out of 14 persons tried to restore the vehicle speed by first depressing the brake pedal and operating the steering wheel while decelerating, and immediately depressing the pedal to the accelerator. In the end, none of them stopped the vehicle completely, and all of them continued to drive the vehicle manually by performing evasive maneuvers using the steering wheel. ​In order to confirm whether this behavior is invariant or not, we have collected data from many collaborators and will present the results later.

​When looking at the steering wheel operation to avoid obstacles in the case of TTC 7 seconds and 5 seconds, the smoothness was different. ​That is, the steering wheel was operated smoothly at TTC 7 seconds, but steeply at TTC 5 seconds. This is probably because the driver responded calmly because there was enough distance to the obstacle at TTC 7 seconds. ​On the other hand, at the time of TTTC 5 seconds, it is considered that the driver hurriedly operated the steering wheel because there was not enough distance to the obstacle. When the distribution at the start of steering operation of 14 persons was examined, TTC of 7 seconds was more dispersed than TTC of 5 seconds. ​It is considered probable that the avoidance operation was performed at the timing of their preference because there was a margin at TTC 7 seconds. ​However, at TTC 5 seconds, there was not enough time to start the avoidance operation immediately, so the distribution did not vary. ​For all 14 persons, the above differences in TTC 7 seconds and 5 seconds steering were common.

After the experiment, many of the collaborators said that they felt impatient because there was not enough time for 5 seconds of TTC. ​However, when the TTC was later tested at 3.6 seconds, all of them avoided obstacles, so the TTC limit was 3.6 seconds or less. Since the take-over was confirmed even at TTC 3.6 seconds, it is unlikely that the take-over request should be submitted at least 3.6 seconds before the obstacle. ​This is because the driver feels insecure when the TTC is tight.

At TTC 7 seconds, all the drivers visually confirmed that there was no vehicle diagonally behind by looking at the right door mirror when changing lanes to avoid obstacles. ​However, when the TTC reached 5 seconds, all of them changed lanes instantly, and they said that they could not check the following cars with the door mirrors. However, looking at the facial expressions of the drivers recorded during the experiment, it was found that everyone was looking at the right door mirror when changing lanes. ​In other words, the driver was unconsciously looking at the door mirror when changing lanes, and he/she could not remember his/her movements because of his/her anxiety. ​Just because the TTC is physically able to avoid obstacles, it's a problem that it forces the driver to operate in ways that make it uncomfortable. ​Therefore, it is recommended that the TTC should be at least 7 seconds with a margin.

However, this experiment was a special situation in which the vehicle ran alone on the course. ​What happens when other vehicles are running together?​ Next, as in the previous experiment, we conducted a test on a driving simulator to see whether the take-over was possible in mixed traffic. ​The TTC is 7 seconds, and the overtaking vehicle approaches from diagonally behind after the take-over request is presented. The timing of the appearance of the passing vehicle, whether or not it is moving, is changed for each experiment to prevent the driver from learning the experiment scenario. ​The number of collaborators in the experiment was 14, the same as in the previous experiment. Of the 14 participants, 13 successfully took-over under various tasks even in the mixed traffic environments. ​However, there was a case in which a driver caused a contact accident only once in several experiments. ​It was an accident in which a passing vehicle diagonally behind was found late, an avoidance operation was impossible, and a deceleration was insufficient, and the vehicle came into contact with an obstacle. ​It is sufficient to show that there are cases in which the take-over did not success, although a total of 100 experiments have only 1 occurrence. ​In other words, the take-over cannot always be established even when there is a margin of 7 seconds in TTC.

​By the way. ​In this experiment, a comparison was made between a case in which the following vehicle is confirmed by a normal door mirror and a case in which a monitor with a liquid crystal display as a substitute for the left and right door mirrors is set on both sides of the meter. ​As a result, in the case of the liquid crystal display monitor, since the vehicle enters the field of view without moving the line of sight like a door mirror, there is no delay in finding the passing vehicle diagonally rearward, and the take-over has been achieved in all the attempts.

​ In the above experiment, when the driver avoided the obstacle, all the drivers finally avoided the obstacle by steering wheel operation. ​This may be because many drivers had little driving experience. Therefore, 32 drivers with more than 20 years of driving experience participated in these driving simulator experiments. ​At TTC 7 seconds, no subtasks were performed and the driver was left to decide what to do during automated driving. Of the 32 passengers, 62% (21 persons) noticed the take-over request, decelerated first with the brake, and then changed lanes by steering to avoid obstacles while accelerating again. ​19% (6 persons) avoided by the steering wheel operation, while the speed was maintained without the brake operation. ​16% (5 persons) decelerated by the brake and stopped completely just before the obstacle. ​The result was that 1 person (3%) stopped after steering to avoid obstacles while decelerating with the brake. ​Therefore, 81% (27 persons) avoided obstacles by steering. ​The number of people who stopped by braking while going straight is 16%, so it can be said that this is a minority. ​As the driving experience increased, it was confirmed that the number of people who stopped without steering increased. ​But that's a minority, and if we take-over while we are driving, the majority will be those who try to keep moving and deal with the situation.

In the above experiment, it was found that a problem may occur when the take-over is performed while the vehicle is running. ​It can be seen that this problem has a problem on the driver side and a problem on the vehicle side. The problem on the driver side is whether or not the driver is in a state in which take-over is immediately possible when the take-over request is issued. ​The problem on the vehicle side is that take-over cannot be supported. Whether or not the driver can take-over is whether or not a forward monitoring can be performed immediately upon the take-over request, the situation can be recognized, and the smooth transition to operation can be made. ​That is, the driver has sufficient alertness. ​Therefore, the necessity of the driver monitor is discussed in order to determine the arousal level of the driver at the time of the take-over request or before the request. ​Should the driver monitor be installed, the driver be constantly monitored during automated driving, and if a decrease in alertness is detected, the warning or stimulus should be given to restore alertness? It would be nice if the driver monitor could accurately monitor the driver's wakefulness, but what if the warning is issued when the wakefulness is not lowered by mistake? ​It's not a serious mistake, but if the driver is enjoying a comfortable automated driving experience, he/she might find the warning offensive.



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