The numbers are better than private automobiles driven by humans, but they cannot exceed the potential of trains and buses because of simple geometry: more spac

The numbers are better than private automobiles driven by humans, but they cannot exceed the potential of trains and buses because of simple geometry: more space is used per person transited when they have to run as a fleet of small, independent vehicles. This makes PRT a fine idea, by itself, at medium densities, but troublesome in the context of existing road and rail systems that are set to be fully roboticized and "shared" in coming years. Each time we squeeze more capacity out of the existing paradigms, PRT loses a little bit of its appeal. The silver lining in this cloud is that the general idea of coordinating traffic better is very promising. Several new PRT-style ideas have a notion of a "modular" highway that smoothly loads taxi-style shared vehicles into trains while in motion, eliminating a major transfer delay. Because the vehicles are shared you don't get the parking issues or the stops that dog traditional rail - just a very smooth, fast point-to-point with a bit of climbing in and out of cabs. The biggest weakness of all existing transportation is that it's "lumpy" and oscillates between overcapacity and overcrowding very quickly, whether it's a highway or a subway. What changes is how this turns into a user disadvantage - either in vehicle congestion and heavy land use impact, or frequent stops and crowded cars.