Design flaw could allow positive train control systems to be disabled, FRA warns | 2021-11-19


Washington – The Federal Railroad Administration has issued a safety advisory to railroads and railroad employees regarding a recently identified interface design issue that relates to how the positive control systems of trains interface with the braking systems of locomotives and cabin cars.

PTC systems are slowdown and emergency stop mechanisms designed to help prevent train accidents and derailments caused by human error.

According to a notice published in September 2 Federal Register, the problem allows a train crew member to bypass a PTC application by manually shutting off the pilot valve / brake lever – commonly known as the cut-off valve – before the PTC system engages the brakes.

“This interface design issue poses a significant safety risk by allowing a PTC system to be disabled and unable to engage the brakes to prevent a train-to-train collision, excessive speed derailment, incursion into an established work area or the movement of a train by a switch left in the wrong position ”, indicates the notice.

Railways are to immediately remind crew members that circumvention of a TPC application is punishable by civil penalty or disqualification for the responsible locomotive engineer / conductor. FRA also encourages railways to:

  • Audit the designs of PTC systems implemented on all types of locomotives and cabin cars.
  • Evaluate to what extent the design of a PTC system could be circumvented by a crew member.
  • Develop and implement a plan to mitigate and / or correct the design problem.
  • Provide FRA with a timetable for carrying out the identified actions.


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