I had one of those "AP moments" yesterday and it really got me thinking. We measured the kid -- she's been waiting literally all summer -- at just over 54" in her sneakers and off we went to Coney Island to ride the Cyclone, since she's finally "this tall". Traffic was awful but both Waze and the Tesla nav took us down NY 9A and through the Brooklyn-Battery Tunnel. A route I'm pretty familiar with since that's how you get to the local Service Center -- it's basically at the Brooklyn tunnel exit. So I know AP is not really happening on 9A (stoplights, unpredictable local traffic) but is good in the tunnel itself unless traffic is really moving at 40+ MPH (tunnel speed limit is 25) which only happens at the off-est of off-hours. Yesterday one of the two tunnel tubes was closed for construction so they had traffic going both directions in the other tube and it was very slow -- 15-20MPH the whole way. I set Autopilot and kept an eye out for anything unusual. Which I was expecting to see outside the car, not inside! Now, this tunnel goes from the tip of Manhattan, under the harbor, passes under one corner of Governor's Island where there's a ventilation shaft, then under more of the harbor to Brooklyn. With traffic in both directions we were in the left-hand tube for our direction of travel, which is unusual but happens a few times a week. I assume that may play some part in what follows, since our heading and position entering the tunnel were 40' or so off the usual path through the right-hand tube. About halfway across something really funny happened: First, the IC display snapped from the in-tunnel view with a countdown of the tunnel distance to "turn right on Barry Road in 250 feet". Then the 15" display warped our position to show us about halfway between the tunnel and the shore. Then the dread "RED HANDS" appeared with no warning Then the IC began to frantically issue us directions all as if we were onshore on the island -- or, more properly, perhaps, had just driven off the island and into the water... turn on Andes Road, Kimmel Road, Craig Road, etc, all the old military roads on the island you can't even legally drive on any more. Finally it just gave up and stopped issuing directions. All this time our position continued to move on the big map, parallel to the tunnel but a noticeable distance to one side. Interestingly, I glanced at Waze on my phone and it showed roughly the same approximate position -- generated I assume from our heading and speed when we entered the tunnel. When we exited the tunnel all was back to normal. But what would have happened in an FSD car? All the cameras, radar, lidar, etc. in the world will not help if the software can fool itself into thinking you're floating in the water when you're in a tunnel, snaps your position to a surface road you couldn't possibly have accessed given your prior path through an underwater tunnel with no exits, etc. Yes, I understand they have to handle cases where the car is on a ferry, etc. but in those cases it won't be in "drive" and won't have AP engaged, so I can't see a way properly functioning AP software should have been so easily fooled. The car drove a mile "in the water". The software ought to know there's a tunnel there, and adjust its expectations accordingly -- particularly, not be fooled into thinking the car's magically popped up on an island. I assume what happened was: The car's map database may show the northeast (left-hand, for our direction of travel) tube as one-way north/westbound -- which it sometimes is, but sometimes isn't. This could be fixed. This probably put our path too far from the nearest lane going in the "right" direction (right-hand tube, right lane?) for the nav system to snap to it with high confidence. Shouldn't they special-case tunnels?! Passing under the ventilation shaft on the island the car got a momentary gps or cellular position fix (hard to believe, but...) Suddenly the car decided we were on the island When it saw us drive "off" the island "into" the water it freaked out and red-handsed us This stuff seems pretty basic. The nav in my Prius got it right a decade ago -- I drove through this and other tunnels plenty of times with no warping -- yes, including at off-hours when the tubes were switched, yes, including tunnels with ventilation shafts that went up to things with roads on them. In an FSD car, I assume this freak-out would have resulted in FSD disengaging and dumping control on the driver -- not good, right? I'm not saying I don't think Tesla can get it right, in this and other cases were limitations of the current nav would pose huge FSD problems. But it's always fascinating to find a new one. Let me just say I hope some of the necessary improvements make it back into older cars like mine!