Railway Signalling & Interlocking

4.3 Routes 83 4.3.7 Route Elements in the Start Zone In some cases, movable track elements which are situated in rear of the route entrance signal in the start zone have to be included into the route functions (figure 4.29). In particular, this occurs with station exit routes in situations where the train starts the route from a scheduled stop, with the previous route of this train already released (chapter Many railways try to avoid such situations in track layout planning by not placing movable track elements in tracks where trains will stop regularly. But particularly in areas with a restricted availability of space, these situations cannot always be avoided. Figure 4.30: Points of the start zone influencing the route speed Figure 4.29: Examples of route elements in the start zone In cases where the movable track element is already occupied by the starting train (figure 29 a and b), locking functions are already fulfilled by the track occupation: However, depending on the interlocking system, additional locking of this element in the route can be applied. In cases where the element can be situated between the train front end position and the route entrance signal (figure 4.29, c and d), this element must always be included in the route locking functions. Additional special requirements in interlocking logic can occur to determine the exact position of the starting train in this context, and in the case of converging tracks to determine the track from which the train starts. The solutions are particular for the interlocking systems and are not be discussed in detail here. A controversial problem of speed signalling occurs if the train uses an element in the start zone in the diverging track (figure 4.29, b and d) and the speed permitted by this element is lower than the speed the route would permit without this element (figure 4.30). The solutions depend on the regulations about the local validity of the speed indication of the signal in rear and which speed has been signalled there (chapter The case that the speed signalled at the station home signal is valid through the whole station (figure 4.9, case 1) is the simpler case in this context. In case of separate speed restrictions for each route (figure 4.9, cases 2a-e), particular attention has to be paid to the element of the start zone concerning speed regulation: