I'm just re-posting what I wrote on SSP:
I don't know if this has ever been noted on this thread (the search feature doesn't let me go back far enough based on the words I was looking for) so apologies if I'm stating the obvious here.
I don't know why I had never realized this sooner, but it had always confused me why the original functional design for the extension noted that the frequency of the Trillium Line would be 8-10 minutes which of course was back in 2015 and then the next time a report was published that mentioned the frequency (I believe it was 2017) suddenly we had a hard 12-minute frequency limit. I had always wondered why this decision ended up being made, and people like roger1818 have suggested that the 12 minute frequency is an attempt to under-promise and over-deliver but while I was reading some documents today it struck me. The original functional design was planned under the assumption that the Trillium Line expansion project would be successful, and in 2015 when that project utterly flopped the functional design was updated to account for that. So no unfortunately, barring a miracle (which will be quite unlikely with the lowest scoring bid), I definitively don't think this could be a case of under-promising.
But wait! There's more. In the set of documents that were accidentally released on Dropbox from a number of months ago there are some meeting notes from the consulting meetings that happened during the planning of the extension. From a meeting in May of 2015 there is this quote:
Yeah, "recent experiences". The decision to go with 80m trains was made following the failure of the expansion project and as we know now has had the effect of turning this from a project that planned to meet the ridership of 2031 into a project that is expected to last until 2048 because of the higher capacity that the longer trains will provide.
Well okay, at least we'll have the capacity we need even if it was ultimately at the expense of frequency. But, although there aren't any meeting notes in the documents from after May 2015, I think the decision to settle on double length trains had some important implications to the effectiveness of the airport spur as well. From the original planning presentations, it was shown that the selected operating model was a mix of branch and direct operations from both Bowesville and the Airport to Bayview that would change depending on demand. Frequency North of South Keys would be 8 minutes, and worst case (using the direct to Bayview from both extension stations option) would see a frequency of 16 minutes to both Bowesville and the Airport. Fine for the airport, not fantastic for Riverside South (though this would obviously not have been used in peak periods) but certainly a lot better than the 24 minute frequencies we'd have if this were done under today's plan. Obviously changing the frequency of the mainline would have negatively impacted the effectiveness of this plan, but at least you'd still be able to run trains direct to the airport during events at the EY Centre right? Well no, because the current design for the Airport Stir still only includes platforms for single-length (41m) trains so you couldn't run direct trains without sacrificing capacity on the main line, which depending on the scenario, may not be ideal.
Now I guess there'd really never be a case, even under a really busy event at the EY Centre, for there to be a need to use 80m trains on the Airport Spur. I don't really have any passenger metrics to back up the idea that the effectiveness of the spur will really be impacted. I can only assume and trust that the planners took that into consideration when they decided to limit the airport spur's platforms. That said, there's an easy fix. Just extend the platforms to the full 75m and leave them totally empty. You'd have the nice part of the station with shelters and covers for the short trains and still have the full platform available if you ever needed to run a large train out there. Maybe that's why the passing track on the spur was extended so much? Ha, wishful thinking.
Obviously this project has been way too far in planning to be changed, but the failure of the expansion project really f****d the plans for the Trillium Line. Would it be too much to say that the expansion project is the single worst [transit] project ever undertaken by the city, or does that still belong to the N-S LRT plan?
I agree with lrt's friend that the limitations of the frequency will limit the attractiveness of the Trillium Line to anyone who doesn't live right by it or in an area where it's the only rapid transit option. I think 8 minutes was the sweet spot between really high frequency like the Confederation Line (overkill) and the old 15 minute frequencies. A really common thing that happens (and I've done this myself) is that people will take either the 7 or 10 from Carleton to get downtown instead of using the "rapid" rail transit option(s in future) to get downtown which, among other things, limits the carrying capacity of those bus routes for local passengers. This happens because people might have just missed the train and it's just not worth walking all the way to the northbound platform for a train that will come in 12 minutes when in the same time two buses on either of those routes will arrive.
But anyawy, the Trillium Line desperately needs more capacity and like I mentioned the thing is already under construction and it's too late to change anything. I'll take what I can get, even though I probably won't be here when it re-opens. Bummer.