Report on signal failure at Grønland Metro Station on 2 March 2020
Railway report 2021/02
On Monday 2 March 2020 at 13.38, a signal error occurred at Grønland Metro Station in Oslo, Norway. Relay 155LO for green light control was incorrectly stuck in the attracted positioning indicating to other systems that it is clear. This caused the main signal T155 to go dark, while the Automatic Train Protection (ATP) equipment onboard the train showed M (drive 50 km/h) and the information to the traffic manager displayed green light. This incident had no direct consequences, but a similar fault elsewhere in the signaling system could have led to a metro train running into the back of another metro train at up to 70 km/h.
The reason why there was no correspondence between the main signal, ATP and the information to the traffic manager is related to the fact that there are different conditions that are used to display a “green” signal. In this case, the main signal became dark because the conditions of the sources that the signal checks were not present to give the green light. The conditions for the ATP and information to the traffic manager to display “green” were not the same as the main signal, and these two systems therefore showed incorrect information.
The investigation has revealed that LO relays (PN-150BL) were used in a way that they are not designed for, which means that over time a contact has been damaged and failed. It may have been a design error in the signaling system from the original implementation in the 1960s, but due to lack of documentation, this has not been possible to determine. However, it has been found shortcomings in Oslo Metro’s system for controlling component properties in 2005, when all LO relays were replaced. In addition, it has been revealed that the maintenance regime for this relay has been inadequate and lacked important prerequisites for detecting damage and defects.
The Norwegian Safety Investigation Authority issues two safety recommendations in this investigation. They concern that Oslo Metro must have a process for replacement and maintenance that ensures that all components of the signaling system can withstand the load they are subjected to, and that ATP and information to the train dispatcher reflect the signal image of the main signals.
Photo: NSIA and Oslo Metro
Published 02.03.2021
Safety recommendation
Safety Recommendation Rail 2021/02T
On Monday 2 March 2020 at 1338, a signal error occurred at Grønland Metro station in Oslo. A safety relay failed when it over time was exposed to a higher load than it was designed for. The investigation has revealed deficiencies in Oslo Metros process for replacement and maintenance of components in the signalling system.
The Norwegian Safety Investigation Authority recommends that the Norwegian Railway Authority follow up that Oslo Metro has a process that ensures that all components in the signalling system can withstand the load to which they are exposed.
Safety Recommendation Rail 2021/03T
On Monday 2 March 2020 at 1338, a safety relay failed and caused a signal error at the Grønland Metro station in Oslo. The error led to different information being given in the main signal, the automatic train protection (ATP) and the information to the traffic manager. Even though the main signal was dark, the ATP and information to the traffic manager displayed “green”.
The Norwegian Safety Investigation Authority recommends that the Norwegian Railway Authority ask Oslo Metro to ensure that ATP and information to the traffic manager reflects the signal image of the main signals.
Facts
| Location | Grønland metro station |
| Occurrence date | 02.03.2020 |
| Type of Transportation | Metro |
| Type of occurrence | Wrong side signaling |
| Rolling Stock | Multippel Unit (MU) |