[derefr]

Why is being fixed-route a bad thing? When you already have city-scale capacity-planning data saying that 100k people make a particular trip on a particular route daily, building fixed infrastructure to accommodate that route usually ends up with a much lower TCO than the equivalent mobile infrastructure. A subway train costs less in maintenance, fuel, and road-congestion than the equivalent number of busses, to serve the same load on the same route. Mobile infrastructure only gains an advantage where the load on a route isn't enough to pay back the capital costs of fixed infrastructure (e.g. busses out to a depopulated exurb.)