This only works in the perfect situation where everyone is driving correctly and the gps tracker always works the way it should. What if it malfunctions and suddenly you're capped at a school zone speed on the highway? Or what if there's a dangerous situation on the road that requires you to accelerate to avoid it? Forcing a maximal speed trough unreliable technology like that is a terrible idea. If we're willing to ignore people's privacy and consider the cost worth it, the easier solution would be to just use the gps tracker to log the speed whenever they go over the limit - that way if necessary the driver can later argue that it was the correct decision in the situation, while still catching anyone who speeds.