You're missing the point.
Even assuming that we'd actually be capable of inventing such a guidance system, and assuming that people wouldn't be horrified by traveling at high speed meters apart, with only an unseen AI between themselves and a fiery death, you still run into the problem of it having to work.
Flawlessly, and perpetually.
You can't have the passengers interfering with the controls in any way, since that would be a recipe for a disaster. Thus, it needs to be under constant control of a computer, and this computer has. to. work.
It can't fail in case of a power-outage, a lightning strike, or any kind of glitch in the code.
And you have to have the ability to upgrade a national guidance network while it's still running. Cars are in use 24/7, so you can't power-down for a reset. Ever.
Nor can you run cars within meters of each other for the simple reason that any vehicle will have moving parts in them, and moving parts have a tendency to break.
So you need a certain safety-distance between vehicles.
Even air-travel, which is the safest way to travel by any margin, is still plagued by things breaking, guidance malfunctions and all sorts of weird stuff.
And this is even before you even start to consider that the accuracy needed would entail a completely new system of geosynchronous satellites, and someone will have to pay for those.
Then there's the grid itself, however it may be constructed.
This is actually how air-travel is done. Invisible corridors between navigation-points, and divided into altitude-layers.
Which is fine as long as you have a fairly small number of possible destinations, there aren't all that many airports around. Discounting all the minor strips, there's somewhere between 30 and 40 thousand.
But now we're talking about a grid encompassing all possible destinations that you could possibly reach in a car.........
In the UK alone there are roughly 27 million households. Now factor in all the shops, restaurants, museums, offices, factories, parking-lots, etc.
Construct a grid that links all the possible combinations of departure and destination, and then plonk into that grid the 33 million cars that are also in the UK.
All moving in three dimensions.
The computing-power needed is astronomical, and again, it can't fail. Ever.
I suppose it might be theoretically possible, but there's no way it'll be in my lifetime.
