Finding a route without congestion is literally impossible for trains stuck on a dedicated track. One little traffic problem shuts down the whole line, includin

Finding a route without congestion is literally impossible for trains stuck on a dedicated track. One little traffic problem shuts down the whole line, including all stations along the route. Since lines are typically connected without redundancy, a failure can partition the network into two disconnected halves. All it takes, in one tiny little spot anywhere on the line: derailment, flood, suicide, stuck switch, malfunctioning sensor, failed motor, wrong kind of leaves on the rails, wrong kind of snow on the rails, broken signal, street-running car crash, tracks blocked off for a crime scene investigation, bomb threat...