How Railway (electrical) signalling work,explain please?

Question

I read in news papers about rail accidents because of signalling faults. I want to know the signalling system in Railways. and i know red to stop, green to go, and what about the middle colour. Please explain

Answer 1

A good question.

Electronic track side signals, also called “fixed signals,” in the US, come in two basic varieties; the “automatic” block signal and the “controlled” signal, with the latter being found within CTC (Centralized Traffic Control) or Interlocking limits.  CTC and Interlocking are methods of operation wherein controlled signals can be set to display “stop” indications, and the switches used in conjunction with these signals are “dual control,” meaning they can be operated remotely by the CTC dispatcher or Interlocking Operator, or by hand in the field after securing permission from the dispatcher.  In these territories, there are still automatic block signals found between the “control points” that are operated by the dispatcher or operator.

The “trigger” is simple enough.  The equipment occupying the rails completes a circuit that activates the automatic block signals. But, a broken rail or other form of track separation will also activate the signals.  Wiring allows for the signals to work together, in succession.

There are many, many different aspects (the appearance of a signal conveying information to an approaching train) so lets not go into that.  But, you are correct that a green aspect indicates “proceed,” a red aspect means stop and a yellow aspect indicates slow to 40 MPH and be prepared to stop at the next signal.  There are variations of all, and even these vary further depending on whether or not displayed by an automatic or controlled signal.  It is far too complicated to address here.

The signal “heads” vary as well.  In the most common “searchlight” type signal head, which we have all seen as a round target on top of the signal mast with a hood over the light for better visibility in bright sunlight, it displays the three colors it can by means of a lens within the signal head that actually changes position mechanically to display the different aspects.  In colder climates they have been known to freeze up, however, conveying erroneous information.  This is a cause of a collision from time to time, but extremely rare.  I encountered only one in nearly thirty years.

Other heads are round as well, with a combination of different lights displayed electronically as opposed to having moving parts inside.  Still others are found that are vertically elongated with multiple lenses that do the same thing.

An earlier type of signal, still in use in some areas, is the old “semaphore” type signals with the “blades” at the top of the signal mast changing position to convey information to an approaching train. Even these are subdivided into upper quadrant and lower quadrant type signals.

Signal masts are also equipped with multiple signal heads so that aspects requiring a combination of colors can also be displayed.

Most automatic block signals get their power from the public utilities providing electricity where the signals are found.  These are backed up with battery power in the event of power failure.  In very remote areas, where electricity is still not yet available, batteries are the primary source of power and are recharged during daylight hours by the use of solar panel arrays of photo-electric cells.

Signals are very comforting to have around as well, as they will tell you not only when to proceed or stop or what route to take, as well as track occupancy, but whether there is any railroad in front of you in the event of a slide or washout that takes the tracks with it.  Even so, they are merely an elctro-mechanical device, and as such, they are subject to failure, just like your toaster.

But, there are back ups in place.  For example, a light that has burned out, leaving the signal dark, is to be interpreted as displaying the most restrictive information that the signal could possibly convey, which in most cases is "stop."  There is also "light out protection" when there are signal bridges over multiple tracks with multple signal heads for each track.  If one light burns out, all will turn red, so a signal's indication will not be misunderstood by another train moving on one of the other tracks.

Unfortunately, there have been accidents caused by human failure on the part of a signal maintainer, or signal man.  A jumper in the wrong place during servicing or testing can do it.  Happily, these are the rarest events of all.

Answer 2

In Railways, as you have said, Red is stop (as is in the rest of the world), Green is Go (No, Really?) and the "middle colour" is Orange (or Amber - depends what you call it) which is a signal that tells the train driver that the next light will be red and that tells him/her to start braking. In some countries, you can find a "double signal" - but the list is exhaustive.

I hope I have managed to answer your question,

S.O.

Answer 3

There are several different methods used for railway signaling, such as timetables or block signals. I recommend that you read the article http://en.wikipedia.org/wiki/Railway_sig... which should give you all the information you need.

Answer 4

Railway signalling is a system used on railways to control traffic safely, for example, to prevent trains from colliding. Trains are uniquely susceptible to collision because, running on fixed rails, they are not capable of avoiding a collision by steering away, as can a road vehicle; furthermore, trains cannot decelerate rapidly, and are frequently operating at speeds where by the time the driver/engineer can see an obstacle, the train cannot stop in time to avoid colliding with it. This necessity was at the base of the establishment of strict guidelines for time keeping and railway chronometers in 1891 by the general time inspector Webb C. Ball of Cleveland, Ohio, USA and in 1889 by the UK parliament passing the Regulation of Railways Act 1889 - a series of requirements on matters such as the implementation of interlocked block signalling and other safety measures as a direct result of the Armagh rail disaster in that year.

Most forms of train control involve movement authorities being passed from those in charge of the rail network or portions of it (e.g., a signalman or stationmaster) to the train crew. The set of rules and the physical equipment used to accomplish this determine what is known as the method of working (UK), method of operation (US) or safeworking (Aus.). Not all methods require the use of physical signals and some systems are specific to single line railways.

Answer 5

Railway lines are divided up into sections called "blocks", which are generally but not necessarily about a mile long.  There is electricity running through the rails, and the axles on the trainset cause a circuit to be completed between the rails. This circuit tells the signal system which blocks are occupied.  If the next two blocks are clear, the engineer on the train will see a green ("clear") signal.  If only the next block is clear, a yellow (or orange/amber "approach") signal would be displayed.  If the block ahead of the train is occupied, a red "stop" signal would show.  

The system is mostly automatic and has been in use for a very long time in the US and UK.  There are newer systems that transmit information about the track ahead directly into the cab of the train, but are based on the same foundation as the automatic signal system described above.