On Wednesday, February 27, the TTC presented a report on the derailment at Kennedy on February 4.
My comments here are a paraphase of the narration at the Commission Meeting.
The derailment happened late at night on a train leaving Kennedy westbound. The front truck of the last car in the train derailed with the car moving about a foot off of the rails. As it was dragged about 300 feet through the crossover, the track, signals and other plant in the tunnel were damaged. Getting the train back on the track and out of the tunnel, plus repairs sufficient to allow operations to resume, took a day and a half. Since then, a 15 kph speed restriction on the crossover was needed for safety as the track fastening to the tunnel floor was returned to good condition for regular operations.
This work is expected to complete on February 29 (Friday).
Page 3 shows the normal configuration of an H6 truck. For those unfamiliar with subway car design, a brief explanation. There are two axles and two motors on each truck with the motors mounted at right angles to the axles. The link between the motor and the gearbox is supported by the torque arm assembly (light blue). This link is flexible and the torque arm can pivot on the truck as we will see in following drawings.
In the event this link fails, the supporting torque arm is supposed to be caught by the safety pin (yellow).
Page 4 shows the initial failure of the torque arm link which allowed the entire assembly to drop down onto the safety pin. Where this happened is unknown, but presumably somewhere on the last eastbound trip toward Kennedy.
Page 5 shows the second failure where the safety pin fell out somewhere between Sherbourne and Castle Frank. This allowed the torque arm to fall to the trackbed. From that point on, the assembly started to break apart losing bits and pieces as the train proceeded east. However, note that the torque arm is in a “trailing” position where it can bouce along without snagging on equipment at track level.
Page 6 shows the problem as the train reversed at Kennedy. Now the gearbox is facing into the direction of travel, and when it reaches the crossover, it snags on the rails. The assembly pivots around and lifts the truck clear of the track so that is now dragging along the tunnel about a foot away from the rails. Meanwhile, the other gearbox runs into a restraining rail and pivots 180 degrees from its standard position. The centre pin holding the car into the truck sheared off and the carbody moved about two feet from its normal position relative to the truck.
Page 7 shows the comparison between a new torque arm link and the one that failed. Page 8 shows a photograph of the torque arm itself and the mark made when it fell onto the safety pin. Page 9 shows how the safety pin and its retaining system failed.
Page 10 shows how the assembly has been redesigned. This change has been retrofitted on the entire H6 fleet (the only cars using this truck design). Note how the new restraining plate locks the safety pin into place.
Page 11 shows the new design for the torque arm link. This has been modified to strengthen the part and to eliminate possible wear points that could lead to failure. Replacement parts are now on order and will be retrofitted to all cars.
Pages 13 and 14 contrast the design of the torque arms and their safety pins on the H6 and T1 cars showing the improved design on the T1.
I have already commented at length on how the TTC managed service following this accident and won’t rehash that discussion here. The TTC was extraordinarily lucky that this failure occured late at night in a location and manner where there was no injury, and where the temporary loss of a station did not block the entire line.
I have left this item open for comments, but do not intend to engage in a discussion about car design or maintenance as this is well beyond the technical competence of most of us and I do not want to engage in speculation about such a serious matter.