TC failure classifications
High / Low / Negligible per NR/L3/SIG/10047 Mod 03 — determines FMS risk level, response and sign-back requirements.
High
- SCWO — controlling an auto signal
- SCWO — controlling a signal working in auto / ARS
- SCWO — controlling a controlled signal not working in auto / ARS
- SCWO — controlling a level crossing (except ABCL/AOCL or TMO with driver indication)
- Showing clear where a TC interrupter is broken
- TCOD — 'occupied' TC clearing following correct application of TCOD
- SCWO — route locking maintained yet indication showing clear (USR not timed out) — poster only; the 2026 guidance rates this Low
Low
- SCWO — indication-only failure, interlocking functioned correctly
- SCWO — controlling ABCL, AOCL or TMO level crossings only
- TC operating but drop shunt >0.2Ω below the minimum permissible for that asset
Negligible
- SCWO — short duration and the interlocking has not responded (under 300 ms)
- SCWO — under 1 s 'striking out' across a track-section boundary while the abutting forward track is occupied
- SCWO — under 1 s 'striking in' across a track-section boundary while the abutting rear track is occupied
- SCWO — reported after protection special working is in place
- SCWO — line not used for some time and protected by TS11 (rusty rails)
Hazard index
| Failure mode | RIDDOR | Hazard | Rating | Class |
|---|---|---|---|---|
| SCWO — automatic signal | Yes | Potential unsafe wrong-side condition (false clear) | H9 | High |
| SCWO — signal working in auto / ARS | Yes | Potential unsafe wrong-side condition (false clear) | H7 | High |
| SCWO — controlled signal not in auto | Yes | Potential unsafe wrong-side condition (false clear) | H6 | High |
| Showing clear with TC interrupter broken | Yes | Potential unsafe wrong-side condition (false clear) | H4 | High |
| TCOD — occupied circuit clearing after a correct TCOD | Yes | Potential unsafe wrong-side condition (false clear) | H4 | High |
| SCWO — controlling a level crossing (except ABCL/AOCL/TMO) | Yes | Potential unsafe wrong-side condition (false clear) | H4 | High |
| SCWO — route locking maintained, USR not timed out | No | Limited / protected wrong-side condition | L2 | Low |
| SCWO — ABCL/AOCL/TMO crossing only | No | Limited / protected wrong-side condition | L2 | Low |
| Drop shunt ≥0.2Ω below minimum | No | Limited / protected wrong-side condition | L2 | Low |
| SCWO — indication-only circuit | No | Limited / protected wrong-side condition | L1 | Low |
| SCWO — under 300ms | No | No credible hazard | N0 | Negligible |
| SCWO — sequencing controls effective (SSI8003-82) | No | No credible hazard | N0 | Negligible |
| SCWO — <1s striking out/in at TC boundary with abutting circuit occupied | No | No credible hazard | N0 | Negligible |
| SCWO — after TS11 special block imposed | No | No credible hazard | N0 | Negligible |
| Rusty rails — TS11 arrangements | No | No credible hazard | N0 | Negligible |
Classification per NR/L3/SIG/10047 Mod 03 §10.1 (section 4 of the EM RE(S) Autumn Working Guidance 2026). High classifications are RIDDOR-reportable.
Where RCM has identified railhead contamination effects of any duration and it is positively proved the interlocking did not respond, the event is NOT a wrong-side failure (Appendix A flow chart). Track-section boundary transitions under 1 s with the abutting TC still occupied are Negligible (clause 3.13) but should be actioned as an early warning.
Discrepancy carried into 2026: the 'Classifications of TC failures East Midlands' poster rates 'SCWO — route locking maintained, USR not timed out' as HIGH, whereas section 4 of the 2026 guidance lists it under Low risk (protected, see Appendix A 3.7 & 3.8). Treat as the higher classification until route S&T confirms.