So, we now have a better picture of what happened at Union on NYE:
Right at 12:30am, at peak traffic, a fight erupted on a subway train.
The response to the security incident including de-boarding all the passengers on that full Line 1 train back onto a busy platform and taking the incident train out of service.
When this happened, TTC staff terminated access to both that platform and Union (subway) station temporarily. This contributed to that backup seen in the GO concourse.
The total delay (no NB train, Union access restricted) was 10 minutes, but if that's equal to 2 -3 crush loaded trains, that's several thousand extra people.
The impact also would have been felt upstream/downstream at other Line 1 stations.
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The incident certainly explains a great deal; but I do think it's not a catch-all excuse.
Clearly, there is/was very little slack capacity in service to absorb what was a relatively minor incident. There is also next to no slack capacity in the buildings in question, particularly the TTC portion of Union Station.
This is a real issue.
A future Ontario Line might shave some TTC related crowding; but I think the TTC needs to plan for a higher level of service and to have gap trains in reserve to offset any issues that may arise.
GO needs more service as well.
I don't think there's any good solution to the capacity constraints of TTC Union, which has already been enlarged; though perhaps a review to see if there's any m2 that can be squeezed out when the WWERT work is finally done would be worthwhile.
Union itself (GO/VIA) is another problem. The South Concourse may help, but GO is going to have to get its throughput and service levels well up. This is planned of course, but theory must shift to practice sooner rather than later.
Finally, the fact that the fight and the out of service train are only really coming to light more than a day later is suggestive of fairly poor communication in which many riders were unaware of the problem; not a new story there, but one for which excuses must end, and better results must be delivered.