I remember watching a documentary on Discovery in the early 90s where they showed a motorcade of 10 Audis closely following each other using radar and some magn

I remember watching a documentary on Discovery in the early 90s where they showed a motorcade of 10 Audis closely following each other using radar and some magnetic markers embedded in the road surface. They could maneuver within inches of one another, stop on a dime etc. I wonder how much embedding such passive markers into the new roads would have cost compared to the amount of money pumped into autonomous driving companies so far.