I wonder why these systems aren't linked to GPS and maps, surely you'd be able to calculate that going right into the middle of two fork options isn't going to end well.

GPS by itself isn't accurate enough to determine what lane you're in.

Even WAAS GPS [1] (used by autopilots for airplanes) is specified to be accurate only up to 25 ft, although the measured accuracy is usually around 3 ft.

[1] https://en.wikipedia.org/wiki/Wide_Area_Augmentation_System

I've heard that GPS is only accurate from about 3-5 meter radius. I think this was also in the same thread talking about the government improving it though.