This type of operation is common on commuter lines where most or all trains operate at the same speed. Two or more Main Tracks are each signaled for movement in either direction, and controlled by CTC.) The signals in Rule 251 territory are controlled by track occupancy, not the dispatcher. Double Track has a designated current of traffic for each track, and is signaled only for trains moving in that direction. (“Double Track” is not defined the same as “Two Main Tracks” on Western roads. Rule 251 is usually used with Double Track. Rule 251 allows a train to operate on signal indication, but only with the current of traffic established for the track. Trains need only to observe the controlled signals to obtain movement authority. From a console, now typically a computer screen, the dispatcher remotely controls signals and powered switches, which are most often found at the ends of sidings and at crossovers between main tracks.
The traffic-control machine or computer software is designed so that conflicting authorities cannot be granted. Trains are governed by signal indications, some of which provide movement authority.
Conceptually, CTC is a series of interlockings all controlled by one person.
CTC is commonly found on high- or medium-density lines, where the signal equipment cost can be justified by the reduction in train delays. CTC, sometimes called TCS (Traffic Control System), is familiar to train watchers. Automatic interlockings are most common at the remote crossings of two railroads, and operate on a first-come, first-served basis.Ĭentralized Traffic Control. Interlockings may be manually or automatically controlled. As their name implies, interlockings are arrangements of signal appliances (once mechanical, now electronic) that are designed so that conflicting movements cannot be authorized. Interlocking signals permit movement within the limits of the interlocking plant bounded by those signals. Let’s look at the different types of authority under which trains may move. A few roads (for example, the Long Island Rail Road and the South Shore Line) still have timetable and train order rules, but most of their operations are conducted under CTC or Rule 251. The common types of authority used to direct train movements today are interlocking signals, Centralized Traffic Control (CTC), Rule 251, Track Warrant Control (TWC), Direct Traffic Control (DTC), Form D Control System, and Yard Limits. Maintenance people must also have authority to be on or obstruct the track. There are several types of authorities, but usually only one type is in effect on any given piece of track. Every train must have authority to occupy the main track before it can begin moving. Running a safe operation is not as simple as you might think.