KAVACH – Train Collision Avoidance System (TCAS)

Indigenous Automatic Train Protection (ATP) system of Indian Railways

SIL-4 certified Tested up to 160 km/h (designed for 200) Kernex · HBL · Medha

What is KAVACH?

KAVACH is an automated situational awareness system that provides Automatic Train Protection as well as Collision Prevention capabilities for trains.

  • Protects trains against SPAD, excessive speed and collisions.
  • Continuous update of Movement Authority – the distance up to which the train may travel without danger.
  • Communication between Stationary and Loco KAVACH is SIL-4 certified.
  • Suppliers (Diesel & Electric locos): KERNEX, HBL, MEDHA.
KAVACH system – onboard and stationary (Ver 3.2/4.0)
KAVACH system – onboard and stationary (Ver 3.2/4.0)

Salient features

🛑
Prevention of SPAD
📡
Cab signalling, loop-line speed control
⚡
Over-speed: section, train & PSR
↩️
Roll-back / reverse protection
💥
Side collision in block section
🚆
Head-on & rear-end collision prevention
📯
LC gate auto whistling
🆘
SOS generation & reception
📏
Train length computation
🔀
Shunt limits validation
🏁
Max 200 km/h (tested 160)
🔐
SIL-4 communication

Abbreviations

#Abbr.Full form
1ABSAutomatic Block Signalling
2AWSAutomatic Warning System
3BIUBrake Interface Unit
4CNFMConfirm
5CONFIGConfiguration
6DMIDriver Machine Interface
7EBEmergency Brake
8EEVEmergency Exhaust Valve
9EMEmergency Magnet Valve Isolation
10FSFull Supervision mode
11FSBFull Service Brake
12IODUInput Output Distribution Unit
13IRABIndian Railway Air Brake
14IR-ATPIndian Railways – Automatic Train Protection System
15IRUInterface Relay Unit
16ISIsolation mode
17LP-OCIPLoco Pilot – Operation cum Indication Panel / DMI
18LSLimited Supervision mode
19MAMovement Authority
20NLNon-Leading
21NBNormal Service Brake
22OSOn-Sight mode
23OV / OVRDOverride mode
24PDUPower Distribution Unit
25PGPulse Generator
26PTPost Trip mode
27RFIDRadio Frequency Identification
28RV / REVReverse
29SBService Brake and Standby mode
30SH / SHNTShunt mode
31SIFA Magnet ValveEmergency Magnet Valve
32SM-OCIPStation Master – Operation cum Indication Panel
33SoSSave Our Soul
34SRStaff Responsible mode
35TCASTrain Collision Avoidance System
36TINTrack Identification Number
37TRIPTrip mode
38T&RSTraction & Rolling Stock
39MBTManual Brake Test
40MTBFMean Time Between Failures
41MIEMain Intelligent Equipment
42NMSNetwork Management System
43KMSKey Management System
44RIURemote Interface Unit
45SSPStatic Speed Profile
46ETCSEuropean Train Control System

1. Onboard KAVACH (Loco equipment)

Onboard equipment in loco
  • Vital Computer1
  • Full-duplex radio modems2
  • Pulse generators2
  • RFID readers2
  • Driver Machine Interface (DMI)2
  • RF antennae4
  • GPS & GSM antenna2
  • Brake Interface Unit (BIU)1
MTBF: Onboard Kavach 40,000 hrs · RFID reader, radio modem, GPS/GSM modem 1,00,000 hrs
Onboard KAVACH – equipment & locations
Onboard KAVACH – equipment & locations
KAVACH equipment tree
KAVACH equipment tree
Antenna locations above cab
Antenna locations above cab

RFID reader & tag

RFID Reader (both sides of loco, under truck)

  • 24 V DC supply · IP 65
  • Reads tag from vertical distance of 700 mm
  • Vertical fixing from rail top: 450 ± 50 mm; horizontal offset ± 100 mm
RFID reader

RFID Tag (fitted on track)

  • Gives location data and TIN when loco passes over it
  • Suitable up to 250 km/h · 865–867 MHz · ≥128 bits · IP 68
RFID tag
TagLocation / spacingPurpose
N-Tag (Normal)Max 1000 m; both directionsLocation & TIN – normal and reverse direction
S-Tag (Signal foot)At foot of signals, BSLB, end of berthing tracksIdentify SPAD case
SA-Tag (Signal approach)150–200 mOdometric error correction
T-Tag (TIN discrimination)Point zones with different TINIdentify train route (wrong route → SOS by Kavach)
G-Tag (LC gate)600 m, both directions if requiredWarn road users (horn)
Tunnel tag–For future use
Exit tagExit of TCAS territory, min 2 nos. at 10 mMarks end of Kavach territory

In Version 4 all above tags are replaced by N-Tags.

RF / GPS antennas

RF: 425–430 MHz, up to 250 km/h, IP 67 & flame-proof; each set connects to one radio modem. GPS: time synchronisation of Loco TCAS with other Loco / Stationary units (GPS & GSM are parts of GNSS).

Antennas

Pulse generators

Two speedometer PGs on different wheels – compute speed and distance travelled for absolute location.

Pulse generator

Vital Computer

Interfaces with train interface & brake interface units, two direction-sensing speed sensors, RFID readers. MEDHA VC has counters for Kavach Isolation, EB and SOS messages.

Vital computer

2. Brake Interface Unit (BIU)

Onboard Kavach applies Normal Brake (NB), Full Service Brake (FSB) and Emergency Brake (EB) through the BIU. For a light engine, BIU also activates the Independent Brake (SA9) interface for loco brake-cylinder pressure.

  • Built-in air-brake control logic on a Control Card with analog/digital I/O modules.
  • Works parallel to loco brake system; does not affect brake characteristics.
  • Higher braking prevails (BIU vs LP); BIU braking cannot be reduced by LP.
  • Manual and automatic isolation possible.
Brake commandBP pressure
Normal Brake4.4 ± 0.1 kg/cm²
Full Service Brake3.6 ± 0.1 kg/cm²
Emergency Brake0 ± 0.1 kg/cm²

Extra “Loco Brake Command” is given with NB/FSB/EB if the train is identified as Light Engine.

IRAB interface scheme
IRAB interface scheme
E-70 interface scheme
E-70 interface scheme
CCB interface scheme
CCB interface scheme
CCB: Train Protection Module (TPM) mounted on CCB panel connects by cable (KB P/N-795018) to the CCB unit of WAP-5/WAP-7/WAG-9; connector J3 carries the brake command. A separate SIFA valve on a direct BP line exhausts BP through a large hole for emergency braking.
E-70 BIU (IRU) arrangement
E-70 BIU (IRU) arrangement
EM cock – three-phase loco (E-70 / CCB)
EM cock – three-phase loco (E-70 / CCB)

3. Driver Machine Interface – LP-OCIP / DMI

Controls on LP-OCIP

LEDs: SYSTEM (Green/Red) · EMERGENCY/SOS (Green/Red)

Push buttons: Common/Ack (black) Cancel (blue) SOS (red)

Knob: Leading / Non-Leading · Formation / LE

LP-OCIP panel
DMI of the three makes – Kernex · HBL · Medha
DMI of the three makes – Kernex · HBL · Medha
DMI screen fields
DMI screen fields
#FieldMeaning
1Target TypeType of target ahead – speed restriction, signal aspect or other limits
2LOCO IDUnique identification number of the loco
3Current SpeedPresent train speed in km/h
4Over SpeedNeedle turns orange/red with audio buzzer when permitted speed is exceeded
5Permit SpeedMaximum allowable speed in current section
6Target SpeedSpeed the train should reach, from upcoming track conditions/signal aspect
7Target DistanceDistance (m) to next signal, speed restriction or stop point
8Brake AppliedRed symbol; thickness grows with NB → FSB → EB
9Deceleration ConstantDerived from train configuration selected by LP
10Context MessageWarnings: turnouts, LC gates, PSRs, failure / acknowledgement messages
11Functional KeysSelect train configuration and modes – Reverse, Shunt, Isolation etc.
12Train LengthComputed by Kavach; preset initially, updated after crossing Advance Starter at each station
13Loco LocationChainage in decametres
14Mode NameCurrent mode (Full Supervision, Shunting, Staff Responsible …)
15Mode SymbolSymbol of current mode
16Communication with StationRadio strength with Stationary Kavach of Station / LC / IB / ABS huts
17Movement AuthorityMaximum distance train may travel without danger
18Signal AspectAspect of the approaching signal
19Tag IndicationLast three normal RFID tags – green: read, red: not read
Movement Authority (MA): distance up to which the train is permitted to travel safely.
End of Authority (EOA): location up to which the train may proceed and where target speed is zero.
MA / EOA

4. Stationary KAVACH

Stationary KAVACH architecture
Stationary KAVACH architecture

Radio range 3.5–5 km each side of tower near station; typical height 40 m lattice structure. Antennae for station / IBS / mid-section gate unit give min ≈1.5 km on approach of first signal (typically 4.5 km in Double Distant territory).

GSM: talks to Key Management System (KMS) for authenticity of Stationary Kavach; fault messages to NMS. GPS: time synchronisation among Stationary Kavach, Loco Kavach, NMS, KMS.

Radio exchange between loco and station; Station TCAS and Loco TCAS communicate every 2 seconds; GPS is the time reference.

Detected in all scenarios from track identification, speed, location, train length and direction. In head-on situation, Loco TCAS of both trains apply brakes automatically.

Loco TCAS auto-generates SoS if it stops for default 15 s with MA > 300 m in block section. LP can cancel before or after transmission via DMI. SoS can be generated/cancelled on loco or station by pressing SoS + Common together.

Separate Stationary Kavach unit at mid-section interlocked LC gate and IBS locations outside station tower coverage; also used where remote signalling functions (end cabins / distributed interlocking / LC / IB) must be fetched to a nearby Stationary Kavach unit.
TCAS station equipment
TCAS station equipment
Remote Interface Unit (RIU)
Remote Interface Unit (RIU)
SM-OCIP (HBL)
SM-OCIP (HBL)
SM-OCIP (Medha)
SM-OCIP (Medha)
SM-OCIP (Kernex)
SM-OCIP (Kernex)

5. Sealing, power & switching ON / OFF

Sealing check – before switching ON

Check intactness of Loco Kavach unit, BIU and DMI seals at taking charge. If seal is broken/tampered the Loco Kavach is treated as Defective – inform the loco shed and Traction Loco Controller (TLC) / Power Controller (PRC).

Power supply: 72 V / 110 V DC converted for sub-systems · Diesel 72 V (20–100 V range) · Electric 110 V (60–160 V) · Operating temp −10 °C to +70 °C.

Sealing arrangement – Loco Kavach equipment
Sealing arrangement – Loco Kavach equipment
Switch ON – Onboard Kavach

Cocks first: IRAB – MR & EM cock ON (on BIU) · E-70 – EM (Vital EB) cock of both cabs ON (below A9), IRU Bypass switch of active cab to Normal · CCB 2.0 – EM cock (SIFA isolation) in Cab-1 ON.

  1. Energise loco; develop MR and BP pressure.
  2. Switch ON Kavach power MCB (Rotary switch board / SB-1 / Vital Computer). LP-OCIP boots in ≤ 2 min.
  3. Leading/Non-Leading switch of both cabs in Leading (MU: leading loco LEADING, trailing loco NON LEADING).
  4. Kavach Isolation switch (BIU / IRU / VC) to Normal.
  5. DMI shows Stand By (SB).
  6. Insert/select Reverser key → brake functional test → prompt for train configuration → select configuration, then SR or SHNT + CNFM.
  7. Until SR/SH is selected, Kavach stays in SB.
Switch OFF – Onboard Kavach
  1. Isolation switch to ISOLATION.
  2. IRAB: MR & EM cock OFF · E-70: EM cock of both cabs OFF + IRU Bypass switch to Bypass · CCB 2.0: EM cock in Cab-1 OFF.
  3. Switch OFF power MCB.
Switching procedure flow chart

Start of mission – train configuration

After brake test success, choose train type with Up/Down arrows + Enter and reconfirm. Then select SR or SHNT + CNFM.

Ver 3.2 – train type
Ver 3.2 – train type
Ver 3.2 – passenger types
Ver 3.2 – passenger types
Ver 4.0 – train type
Ver 4.0 – train type
Ver 4.0 – reconfirm
Ver 4.0 – reconfirm

6. Modes of operation (13)

Entry
Default mode after Loco TCAS boots. Also entered when BL key / Reverser is in Neutral, or when EM cock is closed.
Kavach does
Loco TCAS wakes up. The loco/train cannot move. Temporary mode – LP takes it to SR or SH through a series of operations.
LP responsibility
Complete the start-up steps and select SR or SH mode.
Exit
By LP operations (select SR / SHNT + CNFM).
1. Standby (SB) – DMI screen

Entry
Manually by LP after brake test, loco stationary: soft key SR + CNFM. Also automatic from LS when route information is not received.
Kavach does
Supervises loco ceiling speed, roll-back & reverse-movement protection. Prevents head-on / rear-end collision and supervises SoS generation/reception if TIN, direction and absolute location are available.
LP responsibility
Onboard Kavach supervises a ceiling speed without distance limit; LP runs the train on his own responsibility.
Exit
When MA is received from Station Kavach, or automatically into LS / FS when conditions are met.
2. Staff Responsible (SR) – DMI screen

Entry
Only automatic: from SR when only RFID-tag data OR only station communication is received; from FS when communication or 2 consecutive normal tags are lost, or when SSP available < 3000 m / MA. At start of mission Kavach stays in LS until one stop signal is passed in OFF.
Kavach does
Supervises train speed, section speed, PSR and collision targets (if track data valid & direction known). Obeys SoS from station within 3 km radius if RF is established. Supervises MA & turnout speed if radio is good; roll-away & reverse protection.
LP responsibility
While transiting FS→LS or LS→SR, LP must acknowledge the LP-OCIP message with ACK/CANCEL – else brakes are applied.
Exit
To FS when all train & track data incl. SSP up to 3000 m (or MA) is available; to SR when both tag data and communication are lost.
3. Limited Supervision (LS) – DMI screen

Entry
Only automatic: when all train/track data incl. static speed profile & gradient up to 3000 m or MA (whichever is less) is available – and, for a new formation, one stop signal passed in OFF.
Kavach does
In addition to LS: supervises MA and turnout speeds from linked station, measures train length, obeys loco-specific SoS, displays train speed, permitted speed, target distance & target speed. Kavach is fully responsible for speed supervision.
LP responsibility
Keep the train within permitted speed shown on LP-OCIP to avoid unintended brake application.
Exit
Only automatic: to LS (loss of tag/station data), to TRIP (signal crossed at ON), or when LP selects OV / SH / RV.
4. Full Supervision (FS) – DMI screen

Entry
LP presses OVRD + CNFM – normally when there is a genuine reason to pass a signal at ON, MA < 200 m and train at standstill.
Kavach does
Lets the LP pass a Signal at Danger. Supervises against ceiling override speed (default 15 km/h). If MA is extended or override timeout (default 240 s) with section speed & direction known → FS. Obeys SoS; radio active in Kavach area.
LP responsibility
Select OV only after obtaining proper authority to pass the signal at danger.
Exit
Automatically to On-Sight (OS) when the loco crosses the signal at ON.
5. Override (OV) – DMI screen

Entry
Automatically, when in Override mode and the signal at ON is passed.
Kavach does
Allows entry into a section that may already be occupied. Supervised against On-Sight ceiling speed (default 15 km/h). Obeys SoS from Stationary TCAS.
LP responsibility
LP is responsible for checking track occupancy – the track might be occupied.
Exit
Last Stop / Gate / other signals: LSS+200 m or Gate+250 m, otherwise after next signal at OFF. IB Home: IB Home+200 m; Auto signals: after next signal at OFF.
6. On-Sight (OS) – DMI screen

Entry
From FS / LS when a stop signal at ON or EOA+30 m is passed.
Kavach does
Applies Emergency Brake continuously until halt; standstill supervision. Stationary Kavach sends SOS until Trip is acknowledged. (EB application ≠ Trip: over-speed gives EB, but it is a Trip only if EOA is passed. Trip causes: improper LP operation near signal foot, Kavach malfunction, signal flying back to danger with inadequate braking distance.)
LP responsibility
At standstill press P_TRP followed by CNFM to release EB.
Exit
LP acknowledges with P_TRP + CNFM → EB released.
7. Trip (TR) – DMI screen

Entry
After the Trip brake stops the train, LP selects PT + CNFM on LP-OCIP – EB is released.
Kavach does
Supervises ceiling speed of Post Trip mode (default 15 km/h).
LP responsibility
Select PT + CNFM and proceed at 15 km/h.
Exit
Automatically to FS if valid MA, section speed & direction known and the approaching stop signal is crossed at OFF or default 250 m is travelled.
8. Post Trip (PT) – DMI screen

Entry
LP presses REV + CNFM – only at standstill.
Kavach does
Allows direction change from the same cab (orientation unchanged). Supervised against ceiling speed 15 km/h, distance 500 m and time-out 300 s. Obeys SoS; if TIN changes while reversing, Station Kavach generates loco-specific SOS and brakes apply.
LP responsibility
LP must select RV for push-back, else Kavach will not allow reverse movement (roll-back protection).
Exit
Automatically when forward movement is detected.
9. Reverse (RV) – DMI screen

Entry
Only at standstill. Manually from SB / SR / LS / FS: SHNT + CNFM.
Kavach does
Allows shunting at limited speed of 15 km/h. Obeys SOS only from Stationary Kavach.
LP responsibility
Shunt as per station working rules and G&SR. SH mode is for the YARD only – NOT in block section; for shunting in block section select Isolation.
Exit
Manually: SHNT + CNFM again, at standstill.
10. Shunt (SH) – DMI screen

Entry
Rotary switch on LP-OCIP, selected at standstill.
Kavach does
For trailing loco (electrically coupled/remote or not). No active supervision; periodically transmits status to the Kavach network.
LP responsibility
Do NOT select in a single loco/train – Kavach will give no supervision or protection.
Exit
LP turns the rotary switch from Non-Leading to Leading.
11. Non-Leading (NL) – DMI screen

Entry
Automatically on any fault in Onboard Kavach affecting its functioning.
Kavach does
Applies Emergency Brakes continuously.
LP responsibility
LP isolates Kavach (switch-OFF procedure) and runs the train on own responsibility.
Exit
Isolation switch to ISOLATION + close EM & MR cocks → Isolation mode.
12. System Failure (SF) – DMI screen

Entry
Isolation switch to ISOLATION position; EM and MR cocks (wherever applicable) to Close.
Kavach does
Onboard Kavach periodically reports status/mode to NMS. No supervision and no protection.
LP responsibility
Select only when extremely necessary. Entire responsibility for train safety rests on the LP.
Exit
Manually: Isolation switch to Service and EM / MR cocks to Open.
13. Isolation (IS) – DMI screen

Types of transitions

Automatic
System initiated – track conditions or signals
Manual
Loco Pilot initiated – operational needs
Emergency
System failures / critical situations
Mode transitions – Version 3.2
Mode transitions – Version 3.2
Mode transitions – Version 4.0
Mode transitions – Version 4.0
  • When LP responsibility increases through automatic transition, Kavach seeks acknowledgement; if not given, brakes are applied (none at standstill).
  • During transition, supervision is at least that of the least restrictive state; current mode is always shown on LP-OCIP.

7. Version 3.2 vs 4.0 & over-speed action

#Version 3.2Version 4.0
1Train-configuration selection prompts at start of mission are different
2SR can be selected manuallySR cannot be selected manually except at start of mission
3After 2 tags (direction + connectivity) → LSAfter 2 tags → OS mode
42 consecutive tags missed → SR3 consecutive tags missed → SR
5–P_Trip must be followed by OVRD → On-Sight or Reverse
6On-Sight speed always restricted to 15 km/h (configurable)On-Sight speed can be unrestricted, up to MPS
7–Override can be operated on approach of Last Stop / IB signal on run, without stopping
Speed above permittedAction – Ver 3.2Action – Ver 4.0
+2 km/hOver-speed alarm
+5 km/hNormal service brake
+7 / +8 km/h+7 Full service brake+8 Full service brake
+9 / +10 km/h+9 Emergency brake+10 Emergency brake

8. SOS generation & reception

Generation

Manual SOS: in an emergency press SOS + COMMON together on LP-OCIP.

Unusual stoppage SOS: if train stops in block section despite line clear, Kavach asks LP to press ACK/CANCEL within 15 s. If not, SOS is broadcast and brakes applied. To cancel a broadcast SOS press ACK/CANCEL + COMMON together.

Reception & normalisation

Trains approaching the SOS source (within 3000 m of originating station) apply brakes to standstill, then run at max 30 km/h until they pass the source. Normal speed is restored when:

  • SOS is cancelled by the source, or
  • train is > 1500 m away from the source, or
  • no SOS received from source for > 3 minutes.

9. Do's & Don'ts

✔ Do's
  1. Check intactness of Onboard Kavach, LP-OCIP and BIU before switching ON; report broken seal to TLC/PRC.
  2. Read and understand the user manual thoroughly.
  3. Acknowledge LP-OCIP alerts immediately, within the specified time.
  4. Select train configuration (Goods / Formation / Light Engine) and operating modes properly.
  5. Switch ON: required MCBs ON · Isolation switch Service/Normal · EM & MR cocks Open (where applicable).
  6. Switch OFF: Isolation switch to Isolation · close EM & MR cocks · all MCBs OFF.
  7. Handle LP-OCIP with care.
  8. Inform TLC/PRC whenever Onboard Kavach is defective so Railway/OEM staff can attend early.
  9. Follow G & SR provisions and operational requirements issued by Railways.
✘ Don'ts
  1. Don't attempt any repair work.
  2. Don't switch OFF power to Onboard Kavach while it is functioning.
  3. Don't remove modules, connectors, radio modems or antenna connections while Kavach is functioning.
  4. Don't isolate Onboard Kavach while the train is in movement.