Automatic Signaling
Automatic Signaling – Railway GK Capsule
1. What is Automatic Signaling?
Automatic Signaling is a train protection system in which signals operate automatically based on track occupancy and train movement, without manual intervention from a station master or leverman.
It is the highest grade of fixed-block signaling on Indian Railways and is synonymous with Automatic Block Signaling (ABS).
2. Technical Core
| Parameter | Specification (Indian Railways) |
|---|---|
| Block System | Automatic Block (ABS) |
| Track Circuit | 50 V DC / AC track circuits (FIAT/GEE make) |
| Signal Aspect | 4-aspect colour-light (MACL) |
| Braking Distance | 1.2 km (max) between successive signals |
| Gradient Compensation | ±0.4 % allowed without special braking table |
| Overlap | 120 m beyond the stop signal |
| Signal Spacing | 1 km ± 200 m on plain territory |
| Axle Counter Provision | Provided as back-up in electrified sections |
| Fail-Safe Principle | “Right-side failure” – signals fail to RED |
| Maximum Permitted Speed | 160 km/h (Rajdhani corridor) |
| Train Detection | Track circuit + TPR drop |
| Remote Health Monitoring | T-IPIS (TMS) & REMMLOT microprocessor loggers |
3. Historical Milestones
| Year | Event |
|---|---|
| 1928 | First automatic signal commissioned on Bombay–Poona section (GIPR) – 5 km |
| 1957 | All-electric 25 kV section (Howrah–Burdwan) provided with 50 V DC track-circuited ABS |
| 1986 | Centralised Traffic Control (CTC) introduced on Delhi–Ambala |
| 1998 | Rajdhani corridor (NDLS–CNB–MGS) upgraded to 160 km/h ABS with 1 km spacing |
| 2003 | FIAT make jointless track circuit imported from Italy |
| 2012 | RDSO standardises “Auto Signalling 2012” manual |
| 2018 | Ghat-section ABS commissioned on Karjat–Lonavala (58 km) – steepest 1:37 gradient |
| 2022 | “Automatic Signaling with Kavach” pilot on Secunderabad–Wadi (165 km) – first overlay of ATP over ABS |
4. Sub-Systems of Automatic Signaling
- Track Circuit – detects presence of train; 50 V DC immunity ≥ 10 Ω-km.
- Signal Unit – LED cluster colour-light, 110 V DC, 10 mcd luminous intensity.
- Relay Interlocking – Q-style plug-in relays (QRJ, QSPA, QBCA).
- Power Supply – 110 V DC battery float-charged; 30 min back-up.
- Cable Network – 0.9 mm × 4 quad P-44 signalling cable, screened.
- Block Interface – last signal of one station controls first signal of next – “No-need to close block” principle.
5. Operating Rules (GR&SR)
- GR 8.09 – Automatic territory is “absolute block”; driver need not obtain “line-clear”.
- SR 7.14 – “Proceed” aspect in automatic territory does not guarantee track clear up to next station; only up to next signal.
- Caution Order – Permanent speed restriction of 30 km/h for track-machines in ABS section.
- Tokenless – No physical “staff” or “token” required; tokenless block instruments provided only for ** emergencies**.
6. Advantages & Limitations
Advantages
✓ Line capacity ↑ 15–20 % (minimum 2½ min headway).
✓ No station staff required to clear signals.
✓ Permits “skip-stopping” & “green-wave” running.
Limitations
✗ Costly – ₹ 2.5 crore per route km (2023 estimate).
✗ Not economical for single-line or low-density sections (density < 5 trains/day).
✗ Susceptible to ballast resistance drop in monsoon.
7. Current Status (2024)
- Route Km equipped: 6,840 Rkm (≈ 10 % of IR network)
- Zonal leaders: WR (1,450 km), CR (1,200 km), NR (1,100 km)
- Upcoming corridors:
– Vadodara–Ahmedabad (3rd line) – 2025
– Howrah–Kharagpur (4th line) – under ABS + Kavach - RDSO mandate: All 160 km/h routes must have ABS + Kavach by 2030.
8. Quick-Fire Facts (Memory Hooks)
- “Red-Yellow-Green-Yellow” – 4-aspect sequence; double-yellow is “caution” not “attention”.
- “120 m” – overlap length; “1 km” – signal spacing; “50 V” – track circuit voltage.
- “1928 Bombay–Poona” – first ABS; “2022 Secunderabad–Wadi” – first Kavach overlay.
- “No need to close block” – hallmark difference from “absolute block” in manual territory.
BETA
