Week 6 Exam Flashcards
1
Q
When would you be considered Lineside?
A
- You’re between the boundary fence and the area called on or near the line
- You can be seen by the driver of the train
2
Q
When would you be considered on or near the line?
A
If you are within 3 meters of a line and there is no permanent fence between you and the line, or on the line itself.
3
Q
Are you considered on or near the line if you are on the platform?
When would you be?
A
No, unless you are carrying out engineering or technical work within 1.25miles of the platform edge
4
Q
When you would be classes as in a position of safety for the following line speeds?
100mph
101mph
A
100mph - 1.25m (4ft)
101mph - 2m (6ft 6”)
5
Q
What is the voltage carried by the OLE?
A
25,000
6
Q
What is the minimum safe distance that must be kept from a live OLE?
A
2.75m (9ft)
7
Q
What id the voltage carried by the conductor rail?
A
650-750 volts
8
Q
What colour is a Limited Clearance sign and what does it mean?
A
Red & white. No places of safety for the length of the structure.
9
Q
What colour is a No Refuges sign and what does it mean?
A
Blue and white. No places of safety on this side of the line but there may be on the opposite side.
10
Q
When accessing the railway, what must you use if provided?
A
Must use authorised walking routes.
11
Q
How often myst you look up when walking on the track?
A
Every 5 seconds
12
Q
If walking along the track, how long must you be in a place of safety before an approaching train arrives?
A
10 seconds
13
Q
When reporting an accident (other than a rail goods emergency) what should you say?
A
This is an emergency call
14
Q
When reporting an accident, what information must you give about yourself?
A
- Name
- Job role
- Employer
- Where you are speaking from
- Your telephone number or radio call sign
15
Q
When reporting an accident, along with giving the exact location of the accident, what details must you give about the lines that are concerned?
A
Which running lines are definitely blocked.
Those lines that could be blocked.
16
Q
If a line is obstructed, what phrase must you use to describe this and what phrase should you not use?
A
Must use - Line blocked
Must NOT use - Line not clear
17
Q
What does a Signaller have responsibility over?
A
Everyone other than ECO
18
Q
What publication is available to Signallers that contains information about running lines, direction of travel, speeds and milages?
A
Sectional Appendix
19
Q
What is the WON, how often is it issued and what are the sections?
A
Weekly Operating Notice - Weekly
- Safety Notices
- Temporary Speed Restrictions
- Engineering Arrangements
- General Instructions and Notices
- Signalling and Permanent Way Alterations
20
Q
What is the PON, how often is it issues, and what are the sections?
A
Periodical Operating Notice - Every 3 months
- Amendments to Sectional Appendix
- Amendments to the NOI
- Miscellaneous Notices
21
Q
Name five types of level crossings
A
- Automatic half barrier crossing
- Automatic barrier crossing locally monitored
- Manned crossing with barrier
- Foot and barrow crossing
- Barrier crossing with CCTV
22
Q
What is the principle of a Track Circuit Block?
A
A track circuit block system allows a proceed aspect to be shown when
- All track circuits up to and including the overlap of the next stop signal are clean, and all necessary points within the route are detected in the correct position for a train to pass safely
23
Q
What is a signalled move?
A
A movement where a signal has been cleared for a train to proceed
24
Q
What is a un-signalled move?
A
A movement for which no signal has been cleared because the signal is to be passed at danger or no signal is required
25
List three things that you must check before you route a train?
- No other movement that may conflict is to be made first.
- The route is set or free to be set by the interlocking.
- If necessary, you have been given a release by another signaller.
26
Before you allow a movement to occupy a track circuit which would you change the aspect shown at any signal, what must you do?
You must place or keep the necessary signals at danger to protect the movement.
27
What must you also do if another signaller controls that signal?
You must not allow the movement to take place until the signaller confirms that their signal is at danger
28
What is the definition of an overlap?
The distance beyond a stop signal up to which the line must be clear before the previous signal can show a proceed aspect.
29
What must you do before an overlap can be obstructed?
Ensure that any approaching train has stopped at that signal or, if no train is approaching that signal, the previous controlled signal has been placed at danger to protect the movement concerned.
30
How may train descriptions be sent?
- Bells
- Telephone
- Automatically on VDU
31
List 9 things you need to obsessed when a train is passing?
- Door not closed properly
- Insecure load
- Vehicle on fire
- Hot axle box
- Headlight missing/not lit
- Tail light missing/not lit
- Hazard warning lights on
- Driver or guard displaying a red hand signal
- Driver showing train in distress sign - flashing lights/horn
32
When must you provide signal protection at a UWC?
For any movement in excess of 3 minutes or,
| Any large animal, large, low, slow moving vehicles or anything with small wheels
33
If a UWC fails to call back what must the signaller do?
Ensure the driver of the next train to cross is told to-
- Approach the crossing at caution
- Not to cross unless it is safe to do so
- Report back to you and tell you whether the crossing is safe for the passage of trains
34
If a train requires to stop in a section, what information do you require from the driver?
- Type of train
- Where the train is to stop
- Why the train is required to stop
- The approximate time the train is required to occupy the section
35
What is the definition of a signal section?
The line between two stops signals, whether or not they are within the control of the same signal box.
36
What is the definition of a Goods line/loop?
A line that has not been signalled to the standard required for running passenger trains
37
What is the proceed position on a ground position light signal?
Two white lights at a 45% angle
38
What must you do if you become aware that a long time has passed are a train has entered the section?
Try to contact the driver
39
If you cannot find out what is wrong and why the train has taken and unusually long time, what must you do if another line is available?
Stop each train on any adjacent running line traveling towards the overdue train.
Tell the driver of each train the circumstances regarding the overdue train.
Instruct the driver to report what has happened with the overdue train.
Signal normally.
40
Normally you must not allow a train carrying passengers to enter a goods line/loop, When can you allow this to happen?
If it has been published
| In an emergency and authorised by control or SSM
41
Before you allow a train carrying passengers onto a goods line or loop that is not protected by top points from a movement from sidings, what must you be sure of or get an assurance of?
The sidings are clear of vehicles and no movement will approach
All vehicles and traction units on these sidings are properly secured and clear of the line to be used by the train carrying passengers
42
What must you make sure of before you allow a train carrying passengers to approach a stop signal on a goods line/loop?
You must not allow a train carrying passengers to approach a stop signal on the goods line or loop unless the line is clear, and the route is correct set to the stop signal beyond.
43
If you have allowed a train carrying passengers to enter a goods loop, when can you move any points?
Keep all points in the correct position until the train has passed clear of those points or has stopped at the signal protecting those points
44
When can you allow another train to approach a stop signal in a goods line/loop if there is a train carrying passengers within the goods line/loop?
You must not allow another train to approach a stop signal if there is train carrying passengers in the signal section beyond.
45
A train is delayed at a signal. The driver cannot see an obvious reason for the signal being at danger and there is no number on the SPT sign attached to the signal. How soon should the driver contact the signaller?
As soon as possible.
46
How is an AHBC crossing operated?
Automatically bu the train passing over a treadle.
47
Having lowered the barriers on a CCTV crossing, what two things must the Signaller be sure of before pressing the crossing clear?
That the barriers are down and that the crossing is clear.
48
What is an approach control signal?
A signal that will not clear until the train occupies the track circuit
49
What is a junction indicator?
An indication to the driver of which route they will be taking
50
Where would you find flashing yellow lights?
Points diverge, slow down
51
List three uses of a track circuit
Controls some level crossings
Locks routes
Warns of faulty equipment
52
What must you tell your colleague when they come to take duty at work?
Trains
Equipment
Any other
Restrictions
Equipment
Situation
Traffic/trains
53
Except in an emergency, when can you replace a signal when the train has stopped at that signal?
You must inform the driver
54
If you need to replace a signal to danger are you have cleared a signal for a train to start, what must you do before you must that signal back to danger?
When you have informed the driver or,
| Made sure the train does not have a driver
55
When replacing a signal to danger, what two ways could you make sure that the correct aspect is showing?
- Ask the driver
| - Check the panel on your workstation
56
When must you use Stop & Examine?
- Signals of alarm
- An insecure load
- A vehicle on fire
- A hot axle box
57
If you become aware of anything unusual or wrong with a train, what must you do immediately?
- Stop the train
- Stop trains procceding on any adjacent lines from passing the train concerned
- Stop trains proceeding on the same or any other line over the affected area
- Tell the signaller who controls the area from which the train has approached what has happened
- If necessary carry out signalling regulation 4
- If the train enters another signallers area, immediately send the emergency alarm and tell them what has happened
58
If after a train has been examined and there is nothing found that to be wrong, what must you do?
- Stop the first train to travel over the affected area on any line and tell them what has happened.
- Instruct the driver to proceed at caution through the affected area and report the state of the line at a specified point ahead
59
Doors open on a passenger train. What must you do if
- a person has fallen from the train
- It is not known if a person has fallen from the train
- No-one has fallen from the train
- a person has fallen from the train
Examine the line
- It is not known if a person has fallen from the train
Stop the first train on each line and tell the driver what has happened Instruct them to proceed at caution through the affected area
- No-one has fallen from the train
Resume normal working
60
What must you do with any releases?
Keep in normal position
61
If there is a train detained at a signal on approach to the affected section, what must you instruct the driver to do?
Remain at the signal regardless of aspect
62
If you receive the emergency alarm from another signaller, you must?
Acceptance switches to normal
Place all concerned signals to danger before acknowledging the alarm
Contact any trains via Urgent or REC call if necessary
63
You must not allow another train to the affected signal section until the line is clear and safe for the passage of trains, unless it is necessary to do, what?
- Work to and form the point of obstruction, or server an intermediate station or siding, but only if this can be done safely.
- Allow an assisting train into an occupied section
- Allow a train to pass through a diverting junction before reaching the obstruction
- Examine the line
64
What are catch points and where do you find them?
Used where track follows a rising gradient. Details any unauthorised vehicles travelling down the gradient.
65
What is the definition of a traction unit?
Locomotive, multiple unit, self-propelled rail vehicle or road rail vehicle operating in rail mode
66
If a train is detained on the running line at a signal at danger but the driver can see there is an obvious reason for the signal being at the hanger, how long can the Driver wait until they contact the signaller?
Up to 2 minutes
67
What are the obvious reasons that the driver may not have to contact the signaller straight away?
The section ahead is being occupied by a train
| A conflicting movement being made
68
IF you have instructed the driver to wait for the signal, how often must the driver contact you afterwards and what is the exception?
Ever 5 minutes unless the signaller has given other instructions
69
If a driver is unable to contact the signaller by any means, under what circumstances can they leave their cab to use another telephone?
In an emergency
If the driver of a train on another line, or a competent person has told the driver that the signaller has blocked the adjacent line and it is a safe to get down to use another telelphone
70
IF a driver is unable to contact the signaller or signaller is unable to clear the signal, what must the signaller instruct the driver of a train which is to pass another line to do?
Stop opposite the driving cab of the detained train
| Relay the signallers message to the driver of the detained train
71
What must a driver of a shunting movement do if they have been detained an unusually long time?
Remind the signaller in the quickest way possible
72
IF a driver reports flood water, what information must you find out about the flood water?
- Is it up to the bottom of the rail head?
- Is it up to the top of the rail head?
- Is it above the rail head?
- Is it moving and is it likely to dislodge the ballast?
- Has it dislodged the ballast?
73
With snow ploughs, what must you make sure of, with adjacent lines, when ploughing is in progress, and what is the expectation?
You must make sure that adjacent lines are clear of trains when ploughing is in progress. No need for this when ploughs are set to push snow to the cess side as long as the PIC of the ploughing has made sure that there is no danger to train on the other side of the line and you have been told about the arrangements
74
What to the three levels of the rail adhesion mean?
Good - Rail adhesion conditions are good
Expected - Rail adhesion levels are no worse than would be expected for location and environmental conditions
Reportable - Rail adhesion is worse than would be expected for the location and environmental conditions
75
What action must you take for the following, if 'reportable rail adhesion is reported?
Controlled level crossing within the overlap of a signal
AHBC Level crossing
Approach to platform
Dead-end platform
Arrange for the driver of each train to be told about the circumstances unless -the signal is showing a proceed aspect
- Controlled level crossing within the overlap of a signal: Close the crossing to road traffic before each train approaches
- AHBC Level crossing: Select the non stopping mode (where provided)
- Approach to platform: Arrange for the driver of each train booked to call to be told about the circumstances
Dead-end platform: Arrange, if possible, for the platform to be taken out of use
76
What must you arrange for a controlled test stop to happen at the location concerned?
Ops Control tell you that the rail head has been inspected and nothing unusual has been found
Ops Control tell you that the rail head has been inspected and improvement treatment carried out
at least 30 minutes have passed since you were told about the reportable rail adhesion
77
What condition must apple before a controlled test stop can be arranged at a dead-end platform?
That the rail head has been treated
78
Individual point controls: Where points are within the route, what must you ensure before you authorise the movement?
You must make sure that points are correctly set for the safety of the movement, and where necessary,
Set the points using individual point switches and reminder appliances are used
Get confirmation from another signaller that the points are correctly set
Get confirmation from a ground frame operator that the points are correctly set
79
When one train has passed over the route, how can subsequent trains run on unaffected lines? are there any expectations?
Normally, unless you change the position of any points in the affected area.
80
Before authorising a wrong-direction movement, if required, you must make sure there is clearance distance. What distance is clearance distance?
400m.
81
When a wrong-direction movement is required but there is no cab at the leading end of the movement, when is the Driver allowed to drive from another cab?
If there is a competent person on the ground to supervise the movement (shunter / another driver)
82
When is the clearance distance no required for a wrong direction move? (TW7 2.3)
You do not need to carry out this instruction if the movement is proceeding:
to a stationary train or vehicle
to the point of an obstruction
To the detonators protection a possession
Beyond the point at which it will return to a line in the right direction
83
What instructions must be given to the driver before authorising a W.D.M? W.H.U.P.P.A
```
You must tell the driver:
What is required
How far the movement will go
Unworked points have been secured
Points and crossings are set correctly or the movement
Proceed at caution
Arrangements at level crossings
```
84
Working in the wrong direction - on what two occasions can this regulation be used? (TS2 3.6)
To pass over an unaffected line to assist a failed train from the front
To pass over an unaffected line to assist a failed train that is beyond a train that cannot provide assistance
85
A stop signal is blacked out and cannot display any aspect The signal is an open line with no buffer stops. When may the signaller allow a train to approach the defective signal? (TS11 7.1)
You must inform the river of a defective signal, and you must ensure that the line be clear up to and including the overlap of the next stop signal
86
When you have a defective main aspect signal, a driver can approach the signal if?
You may allow a train to approach a signal with a defective main aspect if:
You are sure that signal is showing danger aspect and the signal is kept at danger or,
you are sure it is showing the correct aspect and will not cause the driver to see and incorrect sequence
87
If the above cannot be done, you must inform the driver of the defect and ensure one of the following applies:
The line is clear up to and including the overlap of the next stop signal that is displaying the correct aspect, bryson the defective stop signal
The line is clear up to and including the overlap of the second stop signal beyond a defective distant signal
The line is clear to the buffer stops on a dead-end line
88
Indication failures: If a track circuit fails to clear after the passage of a train or shows occupied for some other reason, but the signal is able to show proceed aspect, what must you make sure of? (TS11-5.2)
You must make sure that:
- The last train has passed through the section
- The next train has been stopped and you have instructed the driver to proceed at caution when the signal is cleared and to report the correct signal aspect if showing at each signal concerned
- The driver has confirmed that each signal has shown the correct aspect
- After a train has passed the signal returns to danger
- There is no indication that an electronic line has failed
If there is more than one route, you must apply this instruction to each route
89
If points are found to be damaged no facing movements until?
- The points have been secured
- The movement can be made safely
- You must keep the protecting signal at danger until the signalling technician tells you that you may clear it
90
If a driver has isolated their AWS - What is the maximum speed a train can travel during poor visibility if the driver is accompanied by a competent person? (TW5-4.5)
40mph
91
TPWS is defective on a passenger train. What is the maximum speed the train can travel id no competent person has been provided for the driver? (TW5-4.5)
60mph
92
What information is required when a train is involved in a dangerous goods incident? (TS1-16.2)
- Train reporting number, if appropriate
- Where and when the incident happened
- Wagon types and numbers if known
- The position of wagons on the train or in the siding
- As many details of the incident as possible
- Whether any railway personnel or members of the public are involved
- The six-character 'Emergency Code' made of four numbers followed by two letters
93
List 5 types of signal/sign that can be passed at danger?
- Main aspect signal
- Position-light signal
- Shunting signal
- Limit of shunt signal or indicator
- Stop board or possession limit board
94
What actions must you take when a train or vehicle proceeds without authority of divides? S.C.A.R _ P.E.A
S- Signals to be placed to danger (Both lines)
C- Crossings (Take necessary actions)
A- Arrange of the line to be cleared ahead
R- Radio Messages (GSMr)
P- Points / divert (to avoid collisions)
E- Emergency alarms
A- Any other actions
95
During poor visibility where can you permit permissive working?
Platform lines
96
If you are not sure there is enough room for a second train, what must you confirm before you clean the signal for that train?
You must get confirmation that there is enough room before clearing the signal for the second train
97
What work will affect the safety of the line?
- Carrying heavy or awkward equipment across or along the line
- Work that will affect the condition of the track
- Digging a hole or stacking equipment close to the line or near the edge of the platform
- Placing a hand trolley on the line
- Using plant within 2m of the line
- Using OTOP that will foul the line
98
When can you authorise a signal to be passed at danger?
- The signal is defective or disconnected
- The signal cannot be cleared because signalling or level crossing equipment has failed
- For shunting purposes, a main aspect or stop signal is to be passed at danger when there is no associated position0light or semaphore shunting signal
- The signal cannot be cleared because a train or movement which has reversed is then required to start from beyond that signal
- An elective train is to pass the signal protecting an isolated section and proceed towards the limiting point
- In an emergency, and then only when authorised by the signal box supervisor or Operations Control, on a TCB a signal is to be passed, so that a train carrying passengers can enter an occupied section to use a station platform. (in an emergency, and then only when authorised by the signal box supervisor or operation control to allow emergency permissive working).
An Engineering train is to:
- Move towards a possession or,
- Leave a line under possession at an intermediate point.
A train is to pass the signal protecting engineering work under the requirements of module TS1 General Signalling Regulations, regulation 13.2 to gain access to:
- A station where the train is required to start back
- A line under single line working
- A siding
The line is to be examined to check that is is clear.
A train is to enter the section to:
- assist a failed train,
- evaluate passengers from a failed train
- Remove a portion of a divided train
- Remove train or vehicles that have proceeded without authority
Single line working applies
Working by Pilotman or modified working applies
99
Other than a Signaller, who else when acting on the Signaller's instructions can authorise a driver to pass a signal at danger?
Pilot man, Hand signaller, Shunter, Competent person
100
In connection with the rue book module S5 Section 2.2. When must you NOT call the route on a panel or workstation?
If you need to keep the entrance signal at danger (unless the signalling technician has disconnected the signal)
I future s a track circuit failure concerned in the route
101
When MUST you call the route?
If there is no track circuit failure and the signal does not need to be kept at danger. You must always call the route.
102
List 6 things you should do to make the line safe before authorising a driver to pass a signal at danger?
- The position of the line concerned is clear and safe for the movement
- The barriers or gates at any controlled level crossings are closed to road traffic
- Operate the points to the position shown on the route card
- Reminder appliances applied
- Ask a competent person, if possible to check the route settings
- Any ground frame release giving access to the route is 'normal' unless it is to be operated for the movement.
103
When you have a defective main aspect signal a river can approach the signal, if?
- The driver has been told about the defective signal
- The signal is showing danger aspect, or the correct aspect and it will not allow the driver to see an incorrect sequence
104
When you have a defective main aspect signal a river can approach the signal, if?
- The driver has been told about the defective signal
- The signal is showing danger aspect, or the correct aspect and it will not allow the driver to see an incorrect sequence
If the above cannot be done, you must inform the driver of the defect and ensure one of the following applies:
- The line is clear up to and including the overlap of the next stop signal that is displaying the correct aspect, beyond the defective stop signal
- The line is clear up to and including the overlap of the second stop signal beyond a distant signal
- The line is clear to the buffer stops on a dead-end line
105
If you suspect that points have been run through, you must not allow any movement to pass over the points in the facing direction unless the signalling technician examines them and tells you?
- The points are not damaged
- The points are damaged but can be used
- The points have been clipped and scotched
106
Describe a 'simple points failure?
- Failure of power operated points that needs one of the following to be set or secured (or both)
- A single point end
- A single point end and co-acting trap point
- Both ends of a crossover
107
Describe a 'complex' points failure?
A failure of power operated points that needs more point ends to be set or secured (or both) than a simple failure. It includes all failures that affect switch diamonds or swing nose crossings
108
Failed trains - Under what circumstances can an assisting train be allowed into an occupied section to assist a failed train?
Remove the rear portion of a divided train
Evacuate passengers from a failed train
Assist a failed train
Remove vehicles which have proceeded without authority
REAR
109
What information do you require from the driver of a failed train?
The exact location of the failed train
Confirm that the failed train will not be removed
Type of assisting train require d
Direction that assistance must approach from
110
When must the driver of a failed train place both assistance protection AND emergency protection?
The train has failed in a temporary block working or emergency special working section
111
Who can authorise wrong direction moves (TW7 1.2)?
```
A signaller
A pilotman (acting on signallers instructions)
A hand-signaller (acting on signallers instructions)
```
112
Before authorising a wrong direction move, to mitigate against risk, what must you do/ensure to make the line safe? (TW7 2.1)
P.U.B.A.G.S.
P- Points are in the required position and locked by facing point locks (where provided)
U- Unworked points are secured
B- Barriers or gates at controlled level crossing are closed to road traffic
A- Automatic half-barrier crossing (ABHC) without wrong direction controls is locally operated
G- Ground-frame release giving access to the route is 'normal' unless it needs to be operated for the movement
S- Signals are set to danger with reminders applied
113
Before a controlled test stop is made, what must you make sure of if permissive working is authorised on a platform line?
Make sure that the platform is clear
114
If the driver who does the controlled test stop reports that the rail adhesion level is still reportable, who must you tell and what must you do?
Inform Ops Control and wait from them to tell you to perform a further controlled test stop
115
What is the definition of permissive working?
Allows a second train to be signalled onto a running line that is already occupied so that more than one train can be in section
116
What class of trains can work permissively on a platform line?
Class, 1, 2, 3, ECS, 5, 9, and 0 and any class of train formed only of MPV when operating as a railhead treatment train or inspection train
117
What class of train can work permissively on a passenger line?
Class 3 to 8 and 0
118
What class of train can work permissively on a goods line?
Class 3 to 8 and 0
119
What are your actions when you have been made aware of train passing with a missing tail lamp or a tail lamp is out?
You must tell the driver that the tail lamp is out or missing
You must find out if the train is complete
120
What regulations require the signaller to send the emergency train alarm?
- Obstruction of the line
- Train or vehicles proceeding without authority
- Stop and examine
121
After Local Control has been taken at an AHBC, what must you instruct a driver to do?
- Approach the crossing at caution
| - Not to pass over the crossing until authorised by a green hand signal shown at the crossing
122
If you cannot obtain a satisfactory picture at a CCTV crossing, what must you do?
- An attendant is required a ta CCTV level crossing if the signaller is unable to get a satisfactory pickier
The signaller must tell the attendant before they lower the barriers
Confirm with the attendant that the barriers are lowered and the crossing is clear before clearing the protecting signal over the crossing
123
Before allowing an attendant to take control at a CCTV crossing, what must the signaller ensure?
- That the protecting signals are at danger with RA
- That route has been set beyond the protecting signals or block markers
- That any train has passed clear of the crossing unless- it has failed between the protecting signal and the crossing
- The driver of the failed train has told you that i will not removed without your position
124
What type of train may be between the protecting signals and the CCTV crossing when local control is taken and what conditions may apply?
- A failed Train
| - The driver of a failed train has told you that it will not be moved without your permission
125
When can you clear a calling on a signal?
When the train has stopped or has nearly stopped at the signal
126
What must be agreed between you and a COSS before granting a line blockage?
- The line to be blocked
- The nature of the work
- The locations between which the work will take place
- The amount of time needed to do the work
- The time after which permission can be given for the line blockage to start
- Which signals or block markets will protect the activity, including those in both direction on a signal or bi-directional line
- Any additional protection needed if the work would affect the safety of the line
- The arrangements if single line working is taking place
- The arrangements at any level crossings affected by the line blockage
127
When must the signal in rear of the protecting signal be maintained at danger during a line blockage?
If the site of the work will be less than 200m from the protecting signal and if work will affect the safety of the line
128
Under which circumstances can a train pass the signal at danger during the line blockage? And who must be told if this is to happen?
SO that a train can reach a station/siding or crossover being used for SLW. You must have told the COSS, IWA, PC or SWL
129
What is an authority number and when is it used?
