When there are driving tasks that these highly automated vehicles can no longer handle, control must be returned to the driver.
To find out the time required for the safe takeover of manual control by a driver, takeover scenarios and secondary tasks of varying complexity were developed and tested in a static driving simulator with 60 subjects aged from 20 to 76.
After a drive with a high level of distraction, 90 percent of the drivers looked at the road again for the first time after 3 – 4 seconds, had their hands on the steering wheel and their feet on the pedals after 6 – 7 seconds and had switched off the automated system after 7 – 8 seconds. However, if you look at the first glance at the mirror and the glance at the speedometer as indicators of awareness of the driving situation, you see that 12 – 15 seconds are required. These reactions, which are required in order to understand the current traffic situation, are thus delayed by up to 5 seconds compared to the reactions of drivers in manual control in the same situation. Part of this period could be saved if drivers in a takeover situation did not have to put down an external device (e.g. a smartphone or tablet computer).
There were very large differences between the drivers for all these reactions. Some drivers showed much quicker reactions. However, there were also some drivers who took longer to react than the times specified above. After some drivers took over control again, collisions or critical driving situations occurred. However, this also occurred to a similar extent in purely manual driving. These situations could have been avoided by means of suitable assistance functions (e.g. an emergency brake assist system). Assistance functions should therefore also be available after takeover by the driver in order to support the driver
The type of takeover situation itself seems to have only a slight impact on the reactions. On the other hand, stronger positive involvement in the secondary task, making it more difficult to interrupt, resulted in slight delays, particularly in the initial steps of the takeover.