I was under the impression that the speed limits in the map data came from some authoritative source, but an experience on the highway today convinced me something else might be going on. Heading northbound on I-95 just outside of I-495 in Virginia, the highway has a 55 mph speed limit that doesn't change. Parallel to the highway on the left, a HOT lane that has a speed limit of 65 mph runs. On version 12.1.2, my wife and I noticed that every time we passed a 55 mph speed limit sign on the right our Model 3 would say the speed limit was 55, but every time we passed a 65 mph speed limit sign on the left the car would say 65. This happened without fail for a few miles until we merged off onto 495. I'm not sure if the Model 3 is actually reading the speed limit signs and interpreting them on the fly, but is it possible that the map data is derived from machine learning trained on footage taken from past drives? Tesla could be testing reading signs, and pushing the limits derived from their NNs as map data.