First published on Christchurch Transport Blog
Transport Accident Investigation Commission (TAIC) has released its report RO-2019-105 into the derailment of a freight train in Wellington Yard on 2 July 2019. This derailment blocked the rail lines into Wellington, and consequently made it impossible for suburban passenger trains to enter or leave the Wellington Station platforms for many hours.
The findings of the report include a determination that a contributing factor in the derailment was the rebuilding of a section of curved track the previous year (2018) with a curve radius of just 71 metres, or about 3 1/2 chains in imperial measurements. Those who are versed in the knowledge of track geometry will immediately see that this is an extremely sharp curve on any corridor, where curves of even five chains radius are almost unheard of in our modern era, although in the infancy of railways in this country, they were relatively common. The most important issues raised by sharp curves are the ability of vehicles with a long rigid wheelbase (such as vehicles with bogies) to go around them, and the restrictions on speed of trains traversing them. Both of these factors can lead to derailments. Limitation on train speeds and accelerated rail wear are key factors for a progressive focus on removing sharper curves from main line tracks which has a key influence in the construction of many deviations and realignments of main line corridors. Branch lines often did not get such improvements as lower train operating speeds were tolerated a great deal more. A 71 metre radius curve should never have got built in a major freight yard in 2018, but at the time Kiwirail had no track standards governing curve radii; in fact, they introduced a standard of an absolute minimum radius of 90 metres two days before the derailment took place.
Other factors in the derailment include the discovery of various faults during a track inspection six months previously, some of which were Class 1 track faults and should have been repaired within 14 days – instead they were closed out without any work taking place; track twist close to the limits of what the wagon could handle; poor maintenance of the derailed wagon (wheel roughness). What was not addressed by the report was the challenge posed by having a derailment able to block all trains in and out of Wellington. Kiwirail has acknowledged this to some extent by suggesting the closed Kaiwharawhara Station needs to be retained for emergency use in such circumstances. Another question is whether the vulnerability of having so many sets of points close together in the entrance of Wellington yard can be mitigated. This would be quite difficult to achieve without taking a lot more land to address track spacing and so forth and would be a major expense. But issues like this have to be considered because of the severe impacts of running down the rail commuter network at such times. Maintaining the alternate station is probably the easiest to achieve for the present.