MCB – OD
Basic Description, Equipment, Layout,
Operation and Circuit Flowchart
This document is not endorsed by Network Rail. It is NOT for installation,
commissioning, testing or maintenance purposes, it is for information only.
Network Rail’s own documents must be followed at all times. REMEMBER this
is uncontrolled and therefore any measurements stated may have changed to
the current standard. Consult NR documents before any work takes place.
©Copyright F. M. Spowart
Page One of Thirteen
Version Two: May 2015
MCB – OD Page Two of Thirteen

Basic Description of MCB – OD system:
The MCB OD system was introduced for two main reasons. Conventional MCB’s using CCTV require
the signaller to confirm that the crossing is clear. There have been a few instances where the
signaller has ‘confirmed’ that the crossing was clear, when in fact it was not, resulting in near misses
and a collision. This is primarily down to lack of concentration when trying to control other crossings
and trains as well.
The other reason is due to many signalboxes being closed and transferred to ROC’s (Rail Operating
Centre’s), and with these closures, many CCTV controlled crossings would become too much for a
single ROC to handle, so crossings would need to be automated.
As half barriers are subject to abuse by road users, full barriers are now preferred. This is where the
MCB – OD (Obstacle Detectors) are now the ‘eyes’ on the crossing.
Used elsewhere in Europe, they have been a success. However, other countries only use a primary
RADAR to detect vehicles. Pedestrians are not accounted for except in the UK where it is a legal
requirement.
Therefore, as well as a primary RADAR called a POD (primary obstacle detector) to detect vehicles,
we have a high-level complimentary LIDAR called a HL COD (complimentary obstacle detector) to
detect adult pedestrians.
As well as the high-level (HL)COD, some crossings, subject to a 9-day census, may have a low-level
(LL)COD where the crossing is used by children frequently. All UK crossings as a minimum have a
POD and a HL COD. ALL the RADAR’s and LIDAR’s MUST confirm that the crossing is clear before
signals will be allowed to clear.
The POD has two multiprocessors that must be in agreement before it allows a crossing clear
confirmation; this is classed as a ‘SIL3’ interlocking (similar to an SSI interlocking).
The POD uses reference reflectors (RR) (triangular mirrors) to determine the area under surveillance
as it scans a 140 degree area. If the POD cannot not see all the RR’s, it will never give a crossing
clear.
The actual (target) area of the crossing is set-up using the on-site PC using reference markers and
angles inputted into the system.
All RADAR’s and LIDAR’s (PODS & CODS) are set-up using a very lengthy process that could take up to
three days to complete per crossing. Level one staff are trained to maintain and fault the equipment
and make minor adjustments to the reference reflectors. Only level two staff are trained to adjust
and set-up the equipment. Under NO circumstances should level one staff alter any other settings
than what they are trained to do, or the RADAR’s could be damaged/moved and give a false crossing
clear. The POD cover shouldn’t have to be removed by level one staff. Serious damage could occur to
the moving RADAR inside and render is out of action. The POD’s alone cost in the region of £60,000.
The LIDAR screens are now protected by automatic electric shutters that keep them clean during idle
mode.
Note: during auto OD operation, all personnel, MUST be outside of the detection zone (the
crossing deck, and outside of the barriers), and behind all COD’s and reference reflectors or a false
obstacle WILL be detected and stop signals from clearing and fail the crossing.
MCB – OD Page Three of Thirteen

On-site crossing clear (CC) and LCU controls (for maintenance, faulting or failure):
LCU: Two control pedestals are provided at the crossing. One is a normal LCU unit which provides
control of the crossing during complete failure, maintenance or engineering work.
CCU: The other pedestal contains the CCU (crossing clear unit) controls. If the OD’s fail and crossing
clear cannot be confirmed by the RADAR and LIDAR’s, then a level crossing attendant (LXA) will be
called. Inside the unit is a three position switch, (left for all signals on, middle for normal (auto) and
right for CCU mode). In CCU mode and once all the barriers are detected down, two buttons will
flash. The LXA will then confirm CC by sight and then push BOTH buttons to confirm this. Signals will
then be able to clear. All signals on is used if an incident then happens after CC is confirmed.
Note: earlier CCU’s were called ‘XCU’s, but should now all be changed.

Basic operation:
The actual crossing circuits in the MCB – OD are very similar to that of a conventional MCB, but
many new relays have been added to do with the OD part.
The crossing sequence is started by a train striking-in and the ‘minimum road open time’ applies.
Roughly at the same time, the POD and COD’s (named as detectors from this point) activate and selftest (6-7 seconds) and the COD shutters lower (2 seconds). After the ambers and red road lights, the
entrance* barriers come down and the detectors scan the crossing.
After scanning and confirming crossing is clear (CC), the exit barriers fall after the 10 second antitrapping* feature (the time given to allow any vehicles or pedestrians to escape if they happen to be
trapped by the entrance barriers).
*On two barrier operation, this is not applicable.
Once the exit barriers have lowered, the detectors scan the crossing. The POD scans three times to
confirm. The COD’s also confirm crossing clear. Once all detectors are in agreement they are given a
STOP command and their outputs are frozen (just as the picture goes blank with CCTV crossings) and
the signal will clear.
Note: Between the DN KR(2) picking and the last clear scan, (OD)(SCAN) JPSR (4 second timer) will
pick and then pick the (CC)SR and only then confirm that the crossing is clear.
The shutters on the COD’s come up after CC confirmation.
If however, the exit barriers come down (or all if two barrier operation) and then an obstacle is
detected within four seconds, they will raise themselves. The RADAR detectors will continue to scan
the crossing. The failure to give crossing clear is registered with interlocking (ABM(2) relay) and a
second attempt will commence (ABM(3) relay). If a second attempt has proved unsuccessful, again
registered by the interlocking (ABM(4) relay), the exit barriers will raise and no longer be in
automatic mode and will effectively ‘fail’ in the air, although this is not technically a failure and an
object has been seen by the detectors and have therefore done their job.
If this happens, intervention will be required by the signaller (he will be given indications saying that
an obstacle has been detected). He will be required to lower the barriers by button then after having
red roads confirmed lit, all barriers intact (BOOM CR) and down indication, they will caution the train
passed the red signal.
Note: Under NO CIRCUMSTANCES will the BOOM CR be strapped out at any time.
MCB – OD Page Four of Thirteen
Once the train has passed, the barriers will be required to be raised by the signaller and then the
crossing will reset. It will then require the S&T to go out and determine the cause of the detection
whether false or not.
Critical failures of the RADAR POD will result in the (OD F2)SR relay dropping and failing the crossing.
If this happens, the POD will require powering down, waiting for one minute, powering back up,
waiting one minute and then the OD RESET button pressing to reset the (OD)(CYC)SR. It will then
take approx 30-40 seconds to respond to commands.

Barrier Protection Management (BPM):
On some crossings where they are close to road junctions where there may be a risk to ‘blocking
back’, a system called BPM (barrier protection management) is used. This is where one or more of
the barriers may fall onto a queuing vehicle and therefore rip it off. To overcome this, sensing wires
are cut into the road surface under where the barrier will fall and if triggered will stop the barrier
from lowering AND its opposite one too. BPM indications are provided to the signaller should it be
triggered. Once the vehicle(s) moves clear, the barriers will lower as normal.

DVR, Recording Equipment and ‘Dropbox’:
All OD crossings are equipped with HD video monitoring equipment including red light cameras and
ANPR cameras and a ‘SA380’ datalogger. Both are recorded 24hrs a day onto a DVR. The DVR also
records Redscan (LIDAR COD files) and RWMON (RADAR POD files).
Not only do these provide evidence of possible mis-use and incidents, they are also used to aid in
fault finding, for example a false or real obstacle detection that stopped a crossing clear being given.
A storage system called Dropbox is used at all crossings that enable video footage, datalogger files,
Redscan and RWMON to be downloaded to it and then any person logged in Dropbox will be able to
view them to either prove a failure or for another technician nationwide to read the files and
determine a cause.
Files must be downloaded on site to Dropbox to enable remote viewing. Videos from the DVR can
only be viewed from a PC. All other files can be viewed via a PC or an i-Device, such as an iPad or
iPhone, (app downloaded from the Apple App Store).
Dropbox also contains site specific information, OD manuals and the signallers fault finding (FF)
guide. On no account should any files be deleted from Dropbox unless it was you who originally
posted it and it is no longer required.
DVR files are deleted after 48 hrs so it’s imperative that any evidence is gathered immediately and
stored on to Dropbox should any allegation be made.
For security reasons, Dropbox log-in details and email addresses are not listed on here.
MCB – OD Page Five of Thirteen

Basic crossing equipment layout and brief description:
Note: this must be viewed in colour to appreciate diagram below
˃1.5m
˃4m
‘COD B’
REB
A
B
˃2.5m
‘COD A’
2 to 3m
140 degree Scan area of the POD
Equipment/key
Brief Description
RADAR primary obstacle detector (called the ‘POD’).
Rotating dish inside that scans the crossing at 140 degrees known as the
surveillance area. Its primary function is to detect vehicles on the crossing. The
actual area detected is set by the reference reflectors (see below).
LIDAR complimentary obstacle detector (called the ‘COD’). Primary function is
to detect objects that the POD cannot detect, such as people. Comprises of
either one high level (HL) LIDAR at all times (two minimum per xing). A low level
(LL) LIDAR (two minimum per xing)is fitted when the crossing is frequently used
by pedestrians. Can have up to 6 CODS (12 in total; 6x HL & 6x LL Lidars).
The reference reflectors (or known as corner reflectors). They do not however
define the corners. They are fixed into position and are used as a reference to
where the POD scans to determine the detection area. Anything outside this
area is disregarded.
Scanned area of the HL LIDAR of COD A. This is to within 25mm of the nearest
barrier. It overlaps the scanned area by COD B and covers the whole area within
the crossing and 25mm short of the nearest barrier.
Scanned area of the HL LIDAR of COD B. This is to within 25mm of the nearest
barrier. It overlaps the scanned area by COD A and covers the whole area within
the crossing and 25mm short of the nearest barrier.
MCB – OD Page Six of Thirteen
Scanned area of LL LIDAR of COD B. The scanned area covers the deck of the
crossing, usually to the edge of the BOMACS; (660 – 780mm from the running
edge of the rail)
Scanned area of LL LIDAR of COD A. The scanned area covers the deck of the
crossing, usually to the edge of the BOMACS; (660 – 780mm from the running
edge of the rail)
The Radial Non-Detection Zone. This is a 2 – 5m zone to ensure reliability during
falling snow or heavy rain etc. Even though the nearest COD has its own nondetect zone, the furthest one will detect any objects.
A
B
CCU: Crossing Clear Unit. This is equipped with a three position switch for
SIGNALS ON/NORMAL/CROSSING CLEAR.
‘Signals on’ puts all signals to red. Crossing clear enables a LXA to override the
OD’s and observe crossing clear and depress two buttons below to confirm. This
is for either OD failure or whilst crossing testing/observation of software.
LCU: Local Control Unit. For use to operate the crossing fully when it has either
failed completely or when engineering works on or near crossing. Note that this
has a two minute timer that will render it non-controllable after first being
opened, only if the RAISE button is required.
The detection zones. As seen on the PC in the REDSCAN program. These zones
are labeled B2, B1, A1 and A2.
The buffer zone. This is the area that must be free from fixed objects, such as
pedestals, lighting columns, fences etc etc.
The crossing deck known as the target or surveillance area. 1 metre from the
barriers or any trackside furniture such as lighting columns etc.

Brief description of levels and measurements:
The RADAR (POD):
RADAR
BEAM:
Min: 2m
max: 60m
C3
Radar Heights:
C1: 50min (+22)cm
C2: 50 +5/-2cm
C3: 50min (+28)cm
140x1 degree tranches
C2
Deck
C1
Follows crossing 1m from barrier & crossing furniture
MCB – OD Page Seven of Thirteen
The Reference Reflectors:
Max: 90 degree angle
Less than 60m away
(top of base): 20mm below the nearest rail head. (SPT base used)
Middle of bracket to base starting height: 880mm (final height determined on set-up)
The LIDAR’s (HL & LL COD):
Distance from COD to anti-trespass guards: 460mm
Max 20.4m range from centre of post
2 to 5m non-detect zone
(LL) Height of laser from deck:
LL LIDAR (children frequently use crossing):
100 to 175mm
LL LIDAR: (adult frequently use crossing):
130 to 280mm
Absolute minimum is 100mm.
Deck
(HL) Height of laser from deck:
Min top of beam height: 390mm
Max bottom of beam height: 610mm
Note: LL heights should be as close as possible to maximum height levels as stated.
MCB – OD Page Eight of Thirteen

The operating system:
The MKII DVR and the PC are housed in an REB next to the crossing.
Several passwords are required to enter the DVR (MKI only), RADAR and LIDAR programs for taking
readings or making observations only.
Settings must not be altered by staff without the set-up (Level 2) competence.

Passwords:
The Mark I DVR ONLY (all these should have been upgraded to Mark II):
Username:
1
Password:
1
To access the RADAR program called ‘RWMON’ on the PC:
Username:
None (not applicable)
Password:
H*******L (all uppercase)
To access the LIDAR program called ‘REDSCAN’ on the PC:
Username:
R*****N (all uppercase)
Password:
O***X (all uppercase)
The RADAR & LIDAR program passwords are not all shown for security reasons.

To access the RADAR (POD) program (RWMON) for maintenance purposes:
Important: you must ask signaller for permission and put crossing onto CCU mode in pedestal
before entering software programs or crossing will show failed.
To open program:
1. Open ‘RWMON’ from desktop, and click OK.
2. Question asked ‘reconfig required’.
3. Select ‘Nein’ (no).
4. Select ‘Program’.
5. Choose ‘Password’.
6. Enter Password (see page above).
7. Select ‘OK’.
8. Choose ‘Configuration’.
9. Select ‘Create/change GFR’.
10. Choose the “active GFR file”.
11. ‘CRC checksum’ appears, ‘OK’ it.
12. ‘OK’ the next menu (Note; this contains info for the record card).
13. Choose ‘Configuration’
14. Select ‘Test Mode Target Display’.
Test mode target display appears. To remove the blue crosses to give a clear edge of the
surveillance area, choose ‘Options’ and then select ‘Corner Points’.
To Close the RWMON program:
Important: you must follow these instructions, or the crossing will not return to auto mode.
1. Select ‘Configuration’
2. Choose ‘Test Mode End’
3. Select ‘Program’.
4. Choose ‘End’.
5. Confirm by selecting yes.
6. If you are in CCU mode, put switch back to normal and close the door.
7. Confirm with signaller that crossing is showing auto.
MCB – OD Page Nine of Thirteen

To access the LIDAR (COD) program (Redscan) for maintenance purposes:
To open the Redscan program:
1. Select ‘Redscan’ from desktop.
2. When open, in small window on the left, select the LIDAR you wish to view.
3. Select ‘Connect Detector’ in the top left.
4. Once active, tick box called ‘Vertical’ to give a true view from the COD.
The scanned area will give information on how it is set up. Objects in detection area will
show up as a white circle with a RED outline, these will ‘occupy’ the OD.
Objects outside the detection area that will not occupy the OD will show up as white circles
with BLUE outlines.
To close the Redscan program:
1. Select ‘Disconnect Detector’.
2. Close the program.
3. Confirm by selecting ‘Ja’ (yes).
4. If you are in CCU mode, put switch back to normal and close the door.
5. Confirm with signaller that crossing is showing auto.

Using Dropbox to store POD error files:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
Open RWMON program (see page five).
Select ‘Configuration’.
Select ‘Protocol Data’ at bottom.
Click Document button in middle (C:\Documents and Settings….).
Select ‘My Documents’.
Select ‘Dropbox’.
Choose crossing name if applicable.
Select ‘Support Files’.
Choose RADAR you want to view; POD or COD.
Enter a date and time in this format: YYYY.MM.DD_TTTT (For example: 20150518_0935).
Open
Select at top ‘Protocol’ or ‘Error’ memory to view.
Select ‘Start’. Note: if Protocol is selected, it will count the memory blocks (wait).
‘CRC checksum’ appears, click OK.
View files.
Choose ‘End’.
Close window in normal way.
Use Windows START button > My Documents > Dropbox to check files have stored.
Notes: Reset memory button on step 12 erases last error memory.
In window in step 15, “TAR” means the number of pixels the RADAR cannot see, so the
higher the number the bigger the object.
“CNR” means the number of reference reflectors seen by the POD.

Capturing Redscan screenshots of the LIDAR’s and saving to Dropbox:
1.
2.
3.
4.
5.
6.
7.
8.
Open REDSCAN program (see above).
Choose LIDAR from window on left.
Select ‘Window Capture’.
Select ‘Save’.
Select ‘Dropbox’ file in My Documents.
Name the file in this format: YYYY.MM.DD_TTTT (and the crossing name).
Check in the ‘Dropbox’ folder in My Documents that screenshot has saved.
Close Redscan program (see above).
MCB – OD Page Ten of Thirteen

Circuit Flowchart:
Crossing is set to AUTO with correct indications for the OD’s to work
Train occupies strike-in TC on approach
TPR drops
TAR picks
20 SECOND TIMER STARTS FOR (A LOW) JR &
AFTER 20 SECS...
10 SECOND TIMER FOR (MROT) STARTS &
AFTER 10 SECS...
This is the minimum time
between trains striking in on
opposite lines to ensure
vehicles and pedestrians have
time to exit
(MROT) picks
(A LOW) JR picks
LOWER SR drops
YODALS START SOUNDING
CON SR drops
1st attempt at closure recorded
(ABM)SR (1) drops
(OD) (START) SR picks
(OD) (RUN) picks
HER drops
AMBER ROAD LIGHTS LIT
(OD)ZR drops
(LL COD A) (FRE A) R picks
AFTER 3 SECONDS...
HJR drops
HJPR drops
AFTER 5 SECONDS...
(LL COD A) (FRE B) R picks
(LL COD B) (FRE A) R picks
(LL COD B) (FRE B) R picks
RECR picks
RED ROAD LIGHTS FLASH
RECPR picks (if no lamps failed)
(CON)JPR drops
LOWER R(1) drops
(POD) (ACT B) R drops
(POD) (ACT A) R picks
(CON)JR drops
(UP) KR drops
ENTRANCE BARRIERS LOWER
(POD) (ACT A)SR picks
(POD) (ACT B)ZR picks
A
(A LOW) JR drops
DN KR(1) PICKS
(MROT) drops
B
MCB – OD Page Eleven of Thirteen
B
A
(POD) (FRE B)R drops
(POD) (FRE A)R picks
(POD) (FRE A) SR picks
(POD) (FRE B) ZR drops
NO OBSTICLE DETECTED
THROUGHOUT (TO
(OD)(SCAN)JPSR PICKING)
(OD) (CLR) R picks
(OB.D) SR picks
Box F
(LOWER) (2) CR drops
Refer to these relay
conditions when the OD’s
are scanning and have not
detected an obstacle.
(LOWER) R (2) drops
(LOWER) (2) JR STARTS TIMING
AFTER 10 SECONDS...
(LOWER) (2) JR drops
EXIT BARRIERS LOWER
(DN) KR (2) picks
OBSTICLE IS
THEN
DETECTED
YODALS STOP SOUNDING
(DN)SR picks (BARRIERS PROVED DOWN & LOCKED)
(OD) JR picks
AFTER 4 SECONDS...
(OD)(SCAN) JPSR picks
E
(CC) SR picks (xing confirmed as clear)
XZGR picks
(OD)STOP SR picks
ALL CONDITIONS MET: signal clears
(OD) START JR STARTS TIMING
AFTER 3 SECONDS...
(OD) START SR drops
(OD) (CLR) R drops
(OD) RUN JR drops
(OD) (STOP) SR STARTS TIMING
AFTER 3 SECONDS...
(OD) (STOP) SR drops
A
B
(OD) ZR picks (OD’s Idle mode)
MCB – OD Page Twelve of Thirteen
A
B
The POD and/or COD relays pick and
drop according to which
RADAR/LIDAR has seen the obstacle.
(POD) (FRE A) SR drops
TRAIN PASSES THROUGH AND
ACTIVATES XASR & XUSR IN SEQUENCE,
AFTER ALL CONDITIONS MET, THE (CON)
SR RE-PICKS AND CROSSING RETURNS
TO NORMAL. (This is the same as normal
MCB crossings. (See MCB notes).
(OD) (CLR) R drops
(OB.D)SR drops
Z (RAI) SR(2) picks
1st closure failed
(ABM)SR(2) drops
(ABM)YJR starts
timing
1 of 2 Stick paths
for (ABM)SR(3)
lost
EXIT BARRIERS RAISE
RADARS RE-SCAN CROSSING
(ABM)YJR has
started timing.
After 30
seconds, and
after
Z(RAI)SR(2) has
repicked, it will
hold it up
preventing any
further
attempts to
reclose the
crossing
& CLEAR (NO
OBSTICLE)
Relay conditions as
above (see box F)
(OD) (CLR) R picks
(OB.D)SR picks
Z (RAI) SR(2) drops
(ABM)SR(3) drops
2nd closure attempt recorded
If crossing remains clear 4 seconds after exit
barriers are down the (OD)(SCAN)JPSR picks. Go to
box ‘E’ above and continue.
EXIT BARRIERS DROP
RADARS RE-SCAN CROSSING
A
MCB – OD Thirteen of Thirteen
A
The POD and/or COD relays pick
and drop according to which
RADAR has seen the obstacle.
OBSTICLE
DETECTED
(OD) (CLR) R drops
(OB.D)SR drops
Z (RAI) SR(2) picks
(ABM)SR(4) drops
EXIT BARRIERS RAISE
Alarm to signaller. He will need to
lower on button
Two closures failed.
AUTO function is now
lost, no more attempts
to close crossing will
be made.
Signaller selects LOWER
LOWER NPR picks
(ABM)ZR picks
Z(RAI)SR(2) drops
EXIT BARRIERS LOWER
SIGNALLER CAUTIONS TRAIN
ACROSS THE CROSSING
After the train has passed, and no others are approaching,
the signaller will raise barriers on manual. LC will reset as it
had seen a obstacle and not a fault. Technician will have to
observe detection area and determine the cause.
Copyright F. M. Spowart May 2015 Version Two