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Study finds wide spread of times for resuming control from highly automated vehicle in non-critical scenarios; challenges for designers

Many recent human factors studies of takeover time in automated vehicles have looked at how long it takes a driver to resume control of the vehicle in critical situations in which the driver has a relatively short time span to respond to the takeover request (TOR). However, there has been little investigation into more frequent scenarios for control transitions—such as exiting from a highway.

Now, in a new open-access study published in the journal Human Factors, University of Southampton Alexander Eriksson and Neville Stanton report that under noncritical conditions, drivers needed 1.9 to 25.7 seconds to resume control in a highly automated vehicle. The large range reflects a variety of driver behavior and environmental conditions. The challenge for designers thus becomes accommodating the full range of response times rather than limiting design parameters to mean or median transition times in the switch to and from automated and manual driving modes, the authors suggested.

In the study, the authors observed 26 men and women (ages 20-52) engaged in simulated driving at 70 mph with and without a non-driving secondary (i.e., distracting) task and recorded the response time as the drivers took over or relinquished control of the automated system.

A takeover request was issued at random intervals ranging from 30 to 45 seconds during normal motorway-driving conditions. The authors found that drivers engaged in a secondary task prior to a control transition took longer to respond, posing a safety hazard. The control transition times were substantially longer than those reported in the peer-reviewed literature.

10.1177_0018720816685832-fig8
Boxplot of the takeover reaction time (TOrt) when switching from automated to manual control in the two experimental conditions (no secondary task and secondary task) contrasted with the TOrt of reviewed papers. Eriksson and Stanton (2017) Click to enlarge.

The authors note that their findings can guide policy makers in setting guidelines for how much lead time a driver will need before taking over from the automation.

In this study we found that the range of time in which drivers resume control from the automated driving system was between 1.9 and 25.7 s depending on task engagement. The spread of TOrt in the two conditions in this study indicates that mean or median values do not tell the entire story when it comes to control transitions. Notably, the distribution of TOrt approaches platykurtic when drivers are engaged in a secondary task. This finding implies that vehicle manufacturers must adapt to the circumstances, providing more time to drivers who are engaged in secondary tasks while in HAD mode to avoid excluding drivers at the tail of the distribution.

In light of this consideration, designers of automated vehicles should not focus on the mean or median driver when it comes to control transition times. Rather, they should strive to include the larger range of control transitions times so they do not exclude users that fall outside the mean or median. Moreover, policy makers should strive to accommodate these inter- and intra-individual differences in their guidelines for “sufficiently comfortable transition times.” When drivers were allowed to self-regulate the control transition process, few differences could be found in both driving performance and workload between the two conditions. This finding lends further support to the argument for designing for the range of transition times rather than the mean or median in noncritical situations.

Last, based on the large decrease in TOrt kurtosis when drivers were engaged in a secondary task, it may also be the case that future automated vehicles need to adapt the TORlt [takeover-request lead time] to account for drivers engaged in other, non-driving tasks and even adapt TORlt to accommodate external factors, such as traffic density and weather.

—Eriksson and Stanton (2017)

Resources

  • Alexander Eriksson, Neville A. Stanton (2017) “Takeover Time in Highly Automated Vehicles: Noncritical Transitions to and From Manual Control” Human Factors doi: 10.1177/0018720816685832

Comments

Davemart

The whole notion of the driver being expected to grab back control when the AP does wrong is not realistic, especially when hands off the wheel driving is enabled or encouraged.

Level 4, where the car is responsible for safely parking up if it hits weather or conditions it can't deal with, but which is only available on some roads and weather conditions is the first decent level.

It is being extensively tested this year.

Arnold

About the same as waking from sleep/micro sleep.
Some are better than others.
If the circumstance are endangering, the adrenaline response will be massive.That may be a help or result in panic.Depends if you're an adrenaline junkie.
Bit like waking up to a Trump presidency.


Davemart

'Bit like waking up to a Trump presidency.'

I am hoping that I am still asleep, and will wake up from that one! :-0

Nick Lyons

Level 3 autonomy (driver must take over at any moment) is a total non-starter, IMHO. Level 4 (complete autonomy on designated routes) is doable, since the driven environment is known and controlled. That's the one I expect we will see implemented over the next decade.

Bobcom52

I will be interested to see how this technology responds to large animals dashing across the road.
Some animals can remain still until the vehicle is almost on top of it then it bounds across your path.
This technology would need roads completely sealed from wildlife.

Davemart

Hi Bob.

Automatic emergency braking systems have already done a lot of work on the problem of animals on the road.

Volvo for instance not only have algorithms and sensors designed to protect against large animals, cows and moose, in Sweden but have developed different ones for fast-hopping kangaroos in Australia.

A lot of the problem with the gradual introduction of autonomy via making level 4 where the car is wholly responsible but only operates in certain weather conditions and on certain roads which is the approach I advocate with none of the instantly grabbing the wheel nonsense relies on systematic and progressive analysis and refinement, not wowie-zowie breakthroughs to cars driving NY-LA this year and suchlike flannel.

We can crack it, but it will be a gradual process, with capabilities coming in over time.

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