Reasons for the Stalling of Cruise Robotaxis

Again, a Cruise robotaxi got stuck in San Francisco, this time at a traffic light. After about 13 minutes, technicians arrived in another Cruise, who then manually moved the vehicle away from the intersection.

In the meantime, however, even a Waymo vehicle came to the same intersection and, after a short wait, pushed back and drove around the stuck Cruise. However, in the Waymo – unlike the Cruise – there was a safety driver who took control of his vehicle.

This is not the first time that such vehicles stalled, I have already reported here several times. But how exactly does it come to these incidents that seemingly randomly the robot cabs stop and then no longer continue. I have already reported about some of the possible causes, here I would like to list them collectively:

Mechanical defect, damage to the vehicle: clearly, something is not working on the vehicle or is reported to the car by a (defective) sensor. A flat tire, engine damage, and the like.

Outside the service area: several times in one night when trying to order a vehicle and drive off with it, it switched off and did not move a millimeter. The display screens in the vehicle said “autonomous driving turned off.” These three events all had something in common: they occurred right on a street that was on the border of Cruise Robotaxis’ service area. They probably mistakenly detected their position as being outside the service area, and thus turned off the autonomous driving mode and refused to start or continue driving. There is certainly a need to fine-tune the vehicle’s geolocation.

Collision reported: Once it happened to us on a trip that after getting out we apparently touched the vehicle where so hard (maybe a jacket fastener that banged against the bumper, and the vehicle interpreted that as a collision through built-in sensors). The vehicle did not move any further and the screens in the vehicle displayed the English phrase “Collision reported”.

Of course, it is desirable for a vehicle to stop rather than continue after a collision. Hit-and-run for robotaxis would be a new category of traffic offense. However, a middle ground must be found here as to what collisions can happen. The zipper of a jacket hitting the bumper will not have damaged anything. The vehicle should be able to continue driving. Vandals who intentionally hit the car to make it stop should be treated the same way. As long as no sensor is damaged or, for example, passengers feel attacked, the vehicle should be able to continue. in real accidents, however, the vehicle should of course be able to stop at the point of collision, or move to a safe position.

Emergency Vehicles: if the vehicle detects an active emergency vehicle (police, fire department, ambulance), it drives to a safe place and stops. When it does so, it displays on the screen that it has stopped and may have to stop somewhere else. Typically, this stop lasts only until the emergency vehicles have left the scene and Cruise recognizes that it can resume its drive.

Sensor defect: if one of the sensors (radar, lidar, camera, ultrasound) indicates an obstacle and thus has the upper hand in sensor fusion, even if the signal is false, the vehicle will stop. There can be many reasons why this happens: contamination of the sensor (an insect that has crashed into it), a defective sensor (caused by extreme weather conditions, by vandals, by a hit object like a flying stone, hanging branch…), a badly adjusted sensor, a sensor that has shifted while driving, or a sensor that is blinded or disturbed by intentional or unintentional signals from outside.

Road situation: occasionally a normal looking road or traffic situation may change so much that the Cruise cannot proceed. The road is suddenly impassable by another vehicle or object, and turning or backing up is not possible. Cruise, from what I have observed, do not push back today. They try to get out of a situation by driving forward.

Computer error: plain and simple a programming error, an incorrect response to a situation, or a completely novel situation that the vehicle cannot resolve.

Connection error: if a robot cab needs to keep in constant contact with a central computer (cloud) and this connection is interrupted, resulting in missing data and instructions, then this could also be a reason why vehicles get stuck for safety reasons.

Cyberattack: that’s also a possibility. And we should be happy if the vehicles have only gotten stuck so far and not run amok.

Did I forget anything?

This article was also published in German.


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