There are some great photos around (but I can't find them on the web) showing the trucks moving equipment for the Snowy Mountains scheme on purpose-built narrow and winding roads. Generators just fitting through rock cuttings (chicken and egg there, as the cuttings were built to fit the generators). I suspect that the whole system was closed territory, with traffic running under some sort of movement control. In 1956, I traversed Gillies Hwy (Qld) under such rules: unidirectional, with a change perhaps every hour. I suspect that the distance was too great for every half hour.
No photos, but great reading: <
Roderick B Smith
Rail News Victoria Editor