Earlier quoted context omitted.
Seems incredibly dangerous. Imagine some bad GPS reading warps you from a highway to a school dropoff zone and decelerates you to 20mph
I find it hard to believe that the car would base that solely on GPS readings, it will likely be a combination of multiple systems, including cameras which read signage as you pass it, which is already commonplace in many newer models.
On autopilot they do periodically do absolutely insane stuff like this due to bad map data, gps drift, lack of recent speed sign reading etc
And they are supposed to be best in class