User:Giorgio italy/AutoDispatcher/The prototype

The prototype

Each railroad and country has its own set of rules and its own signaling system.

Signals at Trenton station (USA). Photo by Sturmovik.	Mechanical signals (Germany). Photo by Falk2.

Most safety rules are however based on common principles. The line track is normally divided into sequential segments called blocks. Blocks can be several miles long and their minimum extension is normally sufficient to contain a train and allow it to stop. Some form of detection is employed to determine whether a block is empty or contains one or more trains. Each block is "protected" by signals placed at its entries.

Two signaling systems can be employed to this purpose:

   Permissive signaling: Allows trains to enter occupied blocks, provided they run slow enough to stop short of any obstructions;

   Absolute signaling: Forbids trains from entering an occupied block.

AutoDispatcher implements absolute signaling and does not allow, thus, more than one train at the time in each block.

The use of the blocking system, nowadays fully automated, is normally restricted to full-line. In stations and other areas equipped with turnouts, the situation is more complex and the responsibility of operations is often delegated to a dispatcher (human or computer).

Dispatching panel at Frankfurt main station (Germany). Photo by Urmelbeauftragter.

The dispatcher is however assisted by safety systems to prevent mistakes. Track circuits (similar to those employed by the blocking system) detect the occupancy of tracks and interlocking circuits (or mechanical systems in the early days) ensure consistency between turnouts position and signals aspect, as well as locking of turnouts and signals while a train is transiting. The following basic rules generally apply:

   A train cannot enter occupied tracks;

   Turnouts must be properly set before a train can transit over them;

   Each train must observe speed restrictions implied by its route (in particular when the route includes thrown turnouts)

Switching (shunting) operations may also take place in these areas and are often governed by separate signals, which are however not controlled by AutoDispatcher.

Italian shunting signals. Photo by Jollyroger.	British shunting signals. Image by Nmedlam.	Hungarian shunting signal. Photo by ŠJů.