Cab signalling

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The cab signals in a Chicago 'L' train. The vertical light bar in the middle of the signal indicates the maximum permitted speed for the section of track where the train is currently located.

Cab signalling is a railroad safety system that communicates track status information to the train cab (driving position), where the engineer or driver can see the information. The simplest systems display the trackside signal aspect (typically, green, yellow or red, indicating whether it is safe to proceed or not), while more sophisticated systems also display allowable speed, location of nearby trains, and dynamic information about the track ahead. In modern systems, a speed enforcement system usually overlays on top of the cab signalling system to warn the driver of dangerous conditions, and to automatically apply the brakes and bring the train to a stop if the driver ignores the dangerous condition.^[1] These systems range from simple coded track circuits to transponders that communicate with the cab, to communication-based train control systems.

1 SEPTA cab signalling
2 Positive train control
3 See also
4 References
5 External links

[edit] SEPTA cab signalling

The Southeastern Pennsylvania Transportation Authority (SEPTA) uses a four-aspect cab signal system, and the technical specification for the Silverliner V includes a description of the cab signal system, which uses coded track circuits to transmit an audio frequency electrical signal along the tracks that is picked up by inductive pickups mounted just above the rail at the front of the train. The system uses two frequencies, 100 hertz and 250 hertz, which are modulated at different rates to convey signal information.^[2]

[edit] Positive train control

Positive train control systems can be overlaid onto cab signal systems or can replace them altogether. These include the Incremental Train Control System (ITCS) installed by GE on the Chicago-Detroit route in Michigan and the North American Joint Positive Train Control (NAJPTC) system being testing in Illinois on the Chicago-St. Louis route. The ITCS has been in revenue service since 2002 with speeds up to 90 mph (145 km/h).^[3] Other systems include Alaska Railroad's CAS, CSX's CBTM, and BNSF's ETMS.

[edit] See also

[edit] References

^ Elements of Railway Signaling, General Railway Signal (June 1979)
^ Southeastern Pennsylvania Transportation Authority (August 2005). "Silverliner V Technical Specification" (PDF). Retrieved on 2007-01-10.
^ United States Federal Railroad Administration (2004-12-15). Positive Train Control Overview. Retrieved on January 10, 2007.