[dcuthbertson]

If your goal is to replace rubber tires, then how about going whole hog and turn the entire road system into a railway system? Tires made of steel, parallel tracks, lots of switching, perhaps regional control systems to guide computerized vehicles along the fastest route keeping safe distances between cars, and cars that automatically link and unlink to create dynamic trains along shared routes. I think that would be a very cool system (although outrageously expensive to realize).