Yesterday I wrote a post about the Metro train collision in Washington, D.C. More information on the accident has been released today, so we can use this information to update the (visual Cause Map (visual root cause analysis). (The PDF, which can be opened by clicking on “Download PDF” shows these changes.)First, the injury count has increased to at least 80, so we update the outline. Also, we have discovered that the lead car in the train was a “B” car. (Metro cars are put in pairs, with the lead car ordinarily being an “A” car.) While this might be a cause of the accident, we don’t yet have enough information to link it on our Cause Map. Instead, we can add it to the outline as a “difference”.
Additionally, more information has come to light about the lack of retrofitting or replacement of the old cars, which were not considered crashworthy by NTSB. The reason given for not retrofitting or replacing the cars is because it would be too expensive, as Metro is without dedicated funds (the only major transit system in the country to operate this way).
Investigators have discovered that the operator had successfully engaged the emergency brake. Our previous information, obtained from the unofficial testimony of passengers on the train, was that there was no attempt to stop or slow the train. Now that new evidence contradicts the old evidence, we can remove “No attempt to stop/slow train” as a cause. Instead, the cause for “Train rear-ended stopped train” is “Striking train did not stop”.
One of the causes for “striking train did not stop” is that the emergency brake was ineffective. It was ineffective because it was pulled too late, because the operator was not aware of the stopped train, or because the braking system was not functioning, or both. The causes for “operator unaware of stopped train” have not changed (yet) since our previous version. However, it has been released that the crash happened on a curve, which is a possible cause for the operator being unable to see the other train. Right now there is no evidence to show that the operator was otherwise distracted.
As far as “brake system not functioning”, we now have evidence that the first two cars of the striking train were two months overdue for brake maintenance. We’ll add that as a cause.
We have moved ineffective mechanical override as a cause for the train not stopping. This sytem should have automatically sensed that the two trains were getting too close and stopped the train. One of the causes we had previously was that the operator had overridden the mechanical override, due to operating in manual mode. The investigation has shown that this was not the case, so we can cross out this cause. (We do not delete it from the map so that we know it’s been considered.)
Another potential cause of the ineffective mechanical override is sensor failure. The Metro General Manager has stated that there is no indication of sensor failure; however, there is no evidence that they were functioning properly so we leave it on our map while we wait for more information.
One other new piece of information has been presented. The speed limit at the location of the accident was 59 m.p.h. We’ll add that as a cause of “train moving at considerable speed.” (We still don’t know how fast the train was actually moving, as the train was not equipped with a data recorder.)
Click on “download PDF” to see how the changes were incorporated into the visual root cause analysis (Cause Map). The Cause Map continues to change throughout an investigation.
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