DRD, yes you are absolutely correct as always. I didn't bother mentioning why I am interested in the subject. Because I noticed walking machines such as the Chebyshev's plantigrade could be easily adapted to running on tracks. The machine can be made very lightweight, so in turn the rails can be made from wood, plastic, concrete, aluminum, whatever is available, and raised 8 feet on trestles to eliminate hitting pedestrians, animals, flooding, washouts, potholes. When I see current efforts at autonomous vehicles designed to operate on asphalt roadways, I see a machine that should be on rail