Simplified Bidirectional Signalling is a form of signalling a two-track railway for wrong line movements (i.e. trains running in the Down direction on an Up line and vice versa). As its name implies, SIMBIDS-style bidirectional signalling is done to a reduced standard, which usually means long block sections and no AWS equipment for wrong line running. Additionally, the speed for wrong direction movements will often be quite restricted compared to the normal line speed.
Because of this, its usage is usually restricted to engineering works and emergencies like broken-down trains, infrastructure problems or signalling failures. Usage for regulating purposes (e.g. to let a passenger train overtake a slower freight train) is normally not allowed.
Last edited by GeoffM on 15/09/2016 at 03:00