GPS is not adequate.
You can't tell which lane your in, it's not accurate enough.
You can barely tell whether your on the left 3 lanes or right 3 lanes of a motorway, again the accuracy problem, you usually determine it from the direction (i.e. if the left 3 lanes are heading south and the car is heading south, they are probably on the left 3 lanes).
Are you in the wrong lane facing oncoming traffic? Your Sat Nav doesn't know. If a country lane runs parallel to a motorway it guesses you're probably on the motorway based on how close the signal says you are.
You can't tell direction, since direction is calculated as the differential movement over time. Without accurate position, you need a big interval to even guess at direction.
If you knew location accurately you could determine the edges of the road for example to stop them going into a ditch at night.
You can't for example have 2 GPS receivers and determine direction with any accuracy, again the problem is the poor performance of the public GPS signal. So forget sticking a GPS on the head and tail of a boat as an accurate compass. Forget auto landing of planes using GPS too, it's just not accurate enough without the landing beam to assists it.
Sure the USA provides GPS for free, but only enough to make it uneconomic to make anything better. The higher clock rate is kept back for military use, the newer satellites have new feature, but the public GPS signal is still the old ones.
We can stick to GPS but then USA dictates to us the speed at which we improve our systems. Which is not a good thing.