And tested on a real road in 1986, to demonstrate platooning on a stretch of Interstate in California in 1986. If GM did anything with it between 1956 and 1986 ... I don't know. But for the 1986 demonstration, there were iron cores (iron cylinders maybe 2" long and ¾" in diameter) embedded in the road pavement, and test cars had magnetic sensors to detect where the core is and to follow the path the cores are on. Signal was used in the car to make autonomous steering happen. The cars had forward-looking radar to match speed along the platooning column of cars. Here, aside from the use of the road as the reference for driving path, the cars had different and more modern technologies than I would expect to have seen in the '50s, when I was a pre-schooler.

Motorama was on display at the Museum of Science and Industry in Chicago for numerous decades - 1950's into the 1980s?