PTC Stop Target Where the Wayside Signal Is Clear
CP 88 was cut over six days ago with a new intermediate signal. Since then, eastbound trains receive an onboard PTC stop target about 1,600 ft west of the signal even though the signal displays Clear and the dispatcher's display shows three clear blocks ahead. One crew made a penalty brake application; another cut PTC out without permission and ran 58 mph to the next terminal. The wayside interface unit at the CP was reused from the old installation, and its address was changed during the cutover. The dispatcher tells you, "The signal system is fine, so it has to be the PTC - tell the crews to cut it out until your next test cycle." The next eastbound train is 15 minutes away.
1. Which authority governs here, and can you direct crews to cut PTC out? Explain the reasoning.
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The wayside signal indication is the train's authority. PTC is a safety overlay that enforces that authority and adds protection; it is not a substitute for the signal system, and the signal system is not validated by PTC agreeing with it.
When a Clear signal and an onboard stop target disagree, you do not know which one is wrong. It could be the signal aspect, the coding, the WIU input or address, the PTC track database, or the onboard equipment. Because you cannot yet tell, the safe posture is to treat the more restrictive information as governing and to protect the territory until the mismatch is resolved.
You cannot tell crews to cut PTC out as a workaround. Cutting out PTC is a defined operating action with its own authority, notification, speed and reporting requirements under the PTC operating rules and 49 CFR Part 236 Subpart I, and it is not a signal maintainer's instruction to give over the radio. What you can do is tell the dispatcher the signal system is being verified and that the crew must follow the applicable PTC failure procedure rather than run past a stop target on someone's assurance.
2. Give your troubleshooting sequence at CP 88 to find where the mismatch originates.
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Work backward from the signal to the onboard system.
- Confirm the signal itself: observe the actual aspect, and verify the control machine indication and the coded output for that signal. Confirm nothing is flickering or intermittent.
- At the WIU, verify the inputs that represent the new intermediate signal's aspects - which relay or code contacts feed which WIU terminal - and compare to the as-built wiring for the cutover.
- Verify the WIU's identity on the network: the reused unit's address was changed, and a duplicate or mispointed address is a strong suspect for a stop target appearing where the signal is clear. Check whether the back office is associating this WIU's reports with the correct location.
- Have the PTC group pull the back-office log for the affected trains and compare reported aspects against actual aspects at the time of each event.
- Confirm the new signal's location and aspects exist correctly in the PTC track database. Do not edit the database in the field; a database change is a configuration change requiring the PTC group's process and verification.
- Verify with a test train, or with a locomotive in the affected direction, before releasing normal operation.
3. What has to be reported and recorded, including the crew that cut PTC out without permission, and what conditions do you insist on before normal operation resumes?
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Report and record:
- The mismatch itself, with times, train symbols, signal aspects observed, and onboard indications - this is a PTC system anomaly and, if the signal system turns out to be at fault, a signal failure as well. Route it through the railroad's Part 236/PTC reporting process and the normal signal failure reporting.
- The penalty brake application, including whether it was caused by the mismatch or by an incorrect onboard response.
- The unauthorized PTC cut-out: that goes to the dispatcher and to operating management, not just into your notebook. Running 58 mph with PTC cut out without authority is a rules violation with its own reporting path, and your record of what the crew reported is evidence.
- Your WIU and signal test results, including the as-found condition and the corrective action.
Conditions before normal operation: signal aspects verified, WIU inputs and addressing verified, back-office log agreeing with actual aspects, and a successful verification run in each affected direction. Until those are met, the territory operates under the applicable failure procedure with the more restrictive information governing - not on the assumption that "it has to be the PTC."