It's based upon stupid law. In practice, most drivers who follow the signalling law correctly turn off the signal when communicating the lane change is complete, wihch is when the lane repositioning has been so substantially completed that there's no going back. However, the law geeks interpret the law in such a way that they say the signal must be active until completion of the lane change. The actual writing of the law says you must have the signal on until entirely into the new lane. The law geeks claim that that's the same thing as completion of the lane change, however, even that discounts the full good center-biased positioning within the new lane that takes time to achieve from having been fully in the lane that the law nominally requires. That's mudied by the fact the law as written probably says lane change complete. That's properly discounted by the drivers who realize that the stated purpose of the law is to communicate to other drivers your intent, and that intent is a good communication up to the time that you're already almost completely into the new lane, but if the blinker remains on while completing the last few inches of lane changing, that the communication becomes faulty, since it could be misinterpreted to be changing into another lane. Back when cars had lots of distance between them and were large and beautiful back when the law was written, this was no problem, since you could clearly see the car start the blinker, move from one lane to the other, and stop the blinker, with no intervening obstacles to that view. These days, with so much traffic to road ratio (huge compaction), all you ever catch of any car is a fleeting glipse in a freeze image state of a car moving in four dimensions, and you have to interpret meaning from a single image, and there, the extra blinker on while achieving the final few inch positining becomes dangerous misinformation, miscommunicating a new lane change that is not going to happen. Good drivers know this, which is most seasoned commute drivers.
The Tesla needs to fix this.
This is simple stuff that any Californian American driver who was out of diapers before the 1980s would already know well. However, to the Uber generation, they might Uber, BART, and Shuttle to work and have no idea what driving standards exist, and just "leave it to the lawyers" to write the driving programs. No wonder Tesla autopilots are having trouble figuring out how to drive safely.
