Washington Metro signaling and operation
From Wikipedia, the free encyclopedia
Signaling and operation on the Washington Metro system involves train control, station identification, train signaling, signage, and train length.
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[edit] Train control
During normal operation on revenue tracks (used for passenger services), trains are controlled by an automatic train control system (ATC) which accelerates and brakes the train automatically without operator intervention. However, all trains are manned with train operators who close the doors (they can optionally be set to open automatically), make station announcements, and supervise their train. The operator can switch a train into manual mode and operate the train manually if needed.
Non-revenue tracks (storage tracks, tail tracks, yard tracks) are not equipped with ATC. Green signs with letters reading "START ATC" and "END ATC" mark the beginning and ending respectively of ATC territory.
[edit] Station identification
The system's rail lines run on ten lettered routes. Within these routes, each station is also identified by a letter and number system based on the route letter and the station number in ascending order from the system's geographic center. This is known as the Remote Terminal Unit (RTU) number. The RTU number identifies the station and nearby track controlled by the station's wayside control room to Metro's Central Control. Metro Center, Gallery Pl-Chinatown, L'Enfant Plaza, and Fort Totten have two RTU numbers - one for each level.
Metro's lettered routes are as follows:
- A Route: Metro Center to Shady Grove
- B Route: Metro Center to Glenmont
- C Route: Metro Center to Huntington via Arlington Cemetery
- D Route: Metro Center to New Carrollton
- E Route: Gallery Pl-Chinatown to Greenbelt
- F Route: Gallery Pl-Chinatown to Branch Avenue
- G Route: D&G Junction east of Stadium-Armory to Largo Town Center
- J Route: C&J Junction south of King Street to Franconia-Springfield
- K Route: C&K Junction south of Rosslyn to Vienna/Fairfax-GMU
- L Route: F&L Junction south of L'Enfant Plaza to C&L Junction north of Pentagon via Fenwick Bridge
- N Route (planned): K&N Junction east of West Falls Church to Route 772
There are no H, I, or M Routes. The originally-intended H Route ultimately became the present J Route, and "I" was never used as a route letter. The M Route would likely be assigned to a future route to Lincolnia, branching off from the C Route south of Pentagon station.
[edit] Signaling
Fixed signals are only present at interlockings. They show a red over red aspect for "Stop and Stay", a lunar (white) aspect for "proceed," and a flashing lunar aspect for "proceed on diverging route" (only present on newer interlockings; older interlockings are being updated with signals that show this aspect). Tracks are divided into block sections, which can only be occupied by one train at a time, a method to protect against collisions used by most railway systems worldwide, but there are generally no fixed signals to protect block sections (signals tend to be only at beginning/end of route and just before track switches). Virtual signal aspects are transmitted to the train by a cab signaling system and displayed to the operator in the cab, as well as transmitted to the ATC system. Entry into an occupied block is prevented by an automatic train protection system (ATP), which supervises both manual and ATC operation and stops the train well before it would enter an occupied block.
At switches entering into pocket tracks in a direction reverse to the normal operating direction, there is a "P Signal". The P Signal is a single lunar signal that displays the letter "P" and is found at the entrance to some but not all pocket tracks and other selected main line interlockings in the reverse direction of the normal flow of traffic. Below the P signal on the same post is a punch box to allow the train operator to manually set the switch to the diverting direction (reverse) when the P Signal is lit. The P signal is only lit when a train occupies the two track circuit approaching the P Signal and all possible routes into the interlocking are not occupied.
[edit] Signage
Two trackside signs exist: The "S"-Sign is posted at revenue tracks and indicates to the operator that a station is ahead. It is located at a distance no greater than 1200 feet (365.75 m) before a station platform. The "TB"-Sign is posted to indicate to the operator that an eight-car train (the longest used in the system) is clear of an interlocking ("turnback") when the train front is flush with the sign, and that the train can turn back in the direction from which it came on the opposite track.[1]
[edit] Train length
Trains are usually four or six cars, with a maximum size of eight cars. Usually six or eight cars are used during rush hour and four or six cars during weekends and late evenings. Metro has now begun their phased introduction of eight car trains on the Orange Line during morning rush hour. By the end of this implementation, Metro hopes to end usage of four car trains from the system.
The third rail may be on one side of the track or the other depending on where the train is, but the rail will only be on one side; there are no places where there are overlapping third rail coverage. On a two-car train, both cars are placed so that the operator controls for each train face in the direction away from the other car; this allows the train to be driven forward in either direction depending on which way it has to go. However, this means that in some parts of the system, there are "gaps" in the third rail sufficient that the shoes from one car could leave connection with the third rail on its side before the other car reaches connection with the third rail on its side. This would result in the train being trapped "dead", between third rails and without power.
