Illustrating the implications of moving blocks on railway traffic flow behavior with fundamental diagrams

Many railroads are currently developing advanced train control systems incorporating moving blocks with the potential to shift train separation principles from a system based on discrete control blocks to one where trains directly interact with each other, similar to a highway. This research develops a simple, flexible analytical framework consisting of rail fundamental diagrams describing density-flow relationships for rail traffic in specific situations such as closely following trains operating in platoons, or fleets, or double-track with directional running. It is shown that rail fundamental diagram curves depicting rail traffic flow under fixed blocks exhibit a sawtooth pattern due to the discrete nature of the control blocks. Equivalent curves describing rail traffic flow under moving blocks resemble continuous flow relationships from the highway domain. The proposed methodology can be used for a number of practical purposes including calculating shockwave effects from bottlenecks such as vertical grades, showing the dampening effect of fixed block control systems on rail traffic flow perturbations, and illustrating interactions between trains operating in a fleet, or platoon. As a complement to more detailed but time-intensive methods such as simulation, railway planners and researchers can use the rail fundamental diagram framework to quickly analyze rail traffic flow behavior under different train control systems and operating conditions.