signalling principles

7/27/2019 Signalling Principles

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Signalling Principles

In Plain English

(Reference to masculine gender alsorefers to the female gender!)

Tony Howker March 2011


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A system that Prevents collisions and

derailments!

A Definition of Signalling

(The tool to Manage the Operation of the Railway)


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Look what happens in a collision or derailment!


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How does Signalling do this?

A signalman operator of the Signalling System,

gives instructions to a Driver of a train.

The Instructions started with Handsignals but

then put signalmen controlled coloured lights or

planks of wood on the top of poles and expectedDrivers of Trains to obey their meaning!


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Handsignal

being

exhibited by

the

Signalman.

(He was

called a

policemen

in thosedays

hence the

nickname

for a

signalman

wasBobby)


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A Few Definitions

I think that you know what I mean and

you think I know what you mean but

just to be sure!


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Definitions Route A section of railway line from

a fixed signal to the next

signal may containpoints ornot may continue past nextsignal ifoverlaps are provided

Route

Overlap


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Definitions Signal A means of displaying

an Authority toProceed and the driver

is aware of the limit of

that Authority.


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Definitions Points

Facing Trailing

A moveable section of the

railway that allows trains todivert onto or converge

from another section of

railway

Facing point complete with Facing Point Lock

Diverting Lines

Trailing point Converging Lines


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Definitions Overlap

In the Rear of a Signal

In Advance of a Signal

An Overlap is a section

of railway line beyond astop signal that must be

clear before a train can

be given permission toapproach that signal

from the rear.

Length often varies between a nominaldistance and braking distance

Overlap

In AdvanceIn the Rear


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DefinitionsNormal & Reverse These originally described the

position of a mechanical lever in a

frame and thus related to theposition ofpoints. When relating

tosignals they describe the signal

being at Stop or Red. Nowadays

Normal is a statement that theequipment or system is in a

quiescent state awaiting a

command to control signalling

equipment. Pulling the lever

controlling signals moved the

signal to give proceed authority to

the Train Driver. (Always

assuming that the interlocking

allowed the movement)

This is the

NORMAL

position

This is the

REVERSE

position


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Definitions Interlocking (Original) Originates from the meaning

to interlock between 2 ormore levers in a mechanical

frame

10Worked by Lever

11Worked by Lever

To Move Lever 10 from Normal to Reverse Lever

11 has to be Normal. If Lever 11 is Reverse, Lever

10 cannot be moved from the Normal position and

therefore is Locked Normal in the lever frame. Hence

the word Interlocking

Worked by Lever 9

Normal Position of 11 points willallow a train to pass along the Main

Line The diagram shows the

Normal lie of the points.

If 11 points are Reverse then the

points will allow a train to move

from the Loop Line to join the main

Line by moving Lever 9 to the

Reverse position

Loop Line

Main Line


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Definitions Interlocking (Modern

Definition) & Controls

Can be done using relays, computers

or a combination of both.

This is the name given to the

Equipment and System that

allows the signalling to becontrolled in a safe manner and

the information given to the Train

Driver to also be correct and safe.

The Interlocking also receivesinformation from the trackside.

Today the terms interlocked by

and controlled by are

synonymous and both could be

replaced by required by.

Interlocking

TC A TC BTC C TC D

TC ETC F

TC G

TC H

23101A

101B25

TC J

Indications

Controls

Signalman

RequestsDiagram or VDU


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The Main PrinciplesGiving unequivocal permission to the driver that it is OK for him to proceed

means that -

The line is clear of any other train or obstruction along this route to the limitof Authority

The Signalman will not alter the line or route as long as the authority is valid

If we withdraw the Authority to proceed, we will not be able to alter the line

or route until the train that was given the authority has come to a complete

stand


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Principles for allowing a Main signal

to show a proceed aspect The line must be clear between the

route entrance signal and the exit

signal ahead The overlap must also be clear

Any lines that converge should also

be clear to the protecting signal

All points in the route must be set,locked and detected in the right

position

Trailing points in the overlap at the

exit signal must be locked and

detected normal

The entrance signal of any directly

opposing routes must be proved at

Red and free ofApproach Locking


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Approach LockingBefore we discuss Approach Locking a little piece of Physics!Trains are heavy and travel at quite a reasonable speed and create substantial kinetic

energy

Because this kinetic energy needs to be dissipated, braking to a stop means that trainscannot stop as quickly as cars or trucks they need distance which also means time.

Therefore our trans cannot be driven on-sight as a car or truck can. All signals

capable of showing a stop aspect need to have an advance warning signal at least

Braking Distance before the stop signal. This is often known as a Distant signal.

So when our signalman withdraws a movement authority (i.e. he replaces a signal to redor stop) he cannot rely on the fact that the train driver will have enough time or distance

to be able to bring his train to a stop at the red signal, especially as the warning (or

distant) signal will have been showing an indication that stated that the next signal was

at proceed. This means that the requirement to hold the route locked until the train has

come to a stand must be carried out by Approach Locking

Approach Locking can only be released by proving the train is at a stand at the red

signal or that the train has passed safely through the route which has remained locked

even though the signal at the entrance to this route has been replaced to red in front of

the train.


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Approach Locking

15A 3A 2A 1

When this signal at RedThis signal

shows Caution

Braking DistanceBraking Distance

This signal shows

Proceed at line speed

This signal shows Red

Signal 15 Cleared to ProceedThis signal shows

Proceed at line speed

This signal shows

Proceed at line speedThis signal shows Red

Signal 15 replaced to stop

Train within Braking Distance and

cannot stop before 15 Signal

Route ahead of Signal 15 now Approach Locked only released by

Train at a stand at 15 signal (usually done via a timer having run say 3

minutes), or train passing through route.


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Further Principles

Associated with Locking Approach Locking

Route Holding

Before a signal can clear the

approach locking must be

proved as being applied so

that it is available if

required.

The same applies to route

holding it must be proved

to be applied before thesignal can clear to a proceed

aspect.


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Train Separation The other Principle besides

locking is Train separation.

This is achieved by only allowing

one train at a time into a particular

piece of railway line. This sectionof line is often called a Block It

may or not be equal to Braking

Distance. (Probably longer)

Block Block & Braking Distance

Braking Distance

Braking Distance & Block Braking Distance & Block Braking Distance & Block


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In Plain Language

We have just defined the fundamental principles

of Signalling

Interlocking Principles

&

Train Separation Principles


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Interlocking Principles

No route can be established unless that route is free of any opposing or

conflicting movements or locking

Any points within the route shall be free of locking or set in the required

position

The route should be unoccupied by trains or other obstructions before the exitsignal can be allowed to show a proceed aspect

Any points in the route shall be locked and detected in the required position

Any Overlap at the exit signal shall be clear of trains and any opposing or

conflicting locking Once a proceed aspect has been given to the driver it shall not be possible to

alter the route

It shall be possible to withdraw the authority given to a driver (re-placing the

entrance signal to stop) however it shall not be possible to alter the locked

route until the train has come to a stand or has passed through the route

Finally before allowing a signal to show a proceed aspect to the driver, it must

prove that the route ahead is locked and that the approach locking should be

primed and ready to be activated.


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Train Separation

Only one train shall be allowed in one section of line at a time (Block

Signalling)

Trains need time and distance to brake to a stand from the allowed line speed

signalling should allow for preliminary caution signals and not force drivers

to drive on sight like a car or truck


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A few extra comments

You will note that I have kept to the basic Principles of Signalling,

deliberately not differentiating between speed or route signalling or theaspects shown to a Driver.

Neither have I shown any principles for the application of any sort of

Automatic Train Protection System.

The equipment used for detecting whether a line is clear or obstructed is

outside the scope of signalling principles hence the idea of Plain English


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Remember who the Customer is for

our Signalling


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THE

ENDof MovementAuthority!

signalling principles

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