SPG is responsible for the execution of the plans produced by CDR. Starting from a detailed knowledge about train dynamic behaviour (speed-acceleration curves), SPG generates in real-time the optimal speed profile for each train, in order to make the CDR plan being executed in a safe and fuel-efficient manner. Speed regulation is performed on the basis of train position and speed information, available at fixed rate through GPS-GSM equipments. The regulation takes into account the communication delays in the control loop. An advisory speed is sent to trains whenever a change of speed is required, as result of estimations on the current plan goals and current state of running trains and infrastructure. If, due to new perturbations, SPG detects that it no longer can comply with plan goals, it asks for a new plan from CDR.