At 1,200 people per train, even 15 minute 2WAD does not empty a 30,000 seat venue very fast. Subway helps a lot, but that's 1,000 riders every two minutes at very optimistic headways. Building Line 4 west from Yonge will help.
A 12-car GO Train
has 1800 seats, and a crush load of about 3000 people. So the post-concert train service (every 10 minutes) has a capacity of 18 000 people per hour, which is about the same as each direction of the subway (given that it takes a couple minutes to fill up each subway train, so the best headway is about 4 minutes).
During the first half-hour after the concert, the capacity is approximately:
3x 3000 people - SB GO Train (every 10 minutes)
7.5x 1000 people - NB subway (every 4 minutes)
7.5x 1000 people - SB subway (every 4 minutes)
Total: 24 000 people carried in 30 minutes
It doesn't matter that the GO trains can't single-handedly empty the stadium because most people are not heading to Union anyway. The limitation to the GO trains seems to be demand rather than capacity. The vast majority of people leaving the event head into the subway, presumably because they're going somewhere other than downtown. Thousands of people also head
northbound on the subway to get back to the park-and-ride lots:
Finch W: 347 spaces
Pioneer Village: 1881 spaces
Hwy 407: 550 spaces
VMC: 900 spaces
Total: 3678
Based on the photos from the Stray Kids concert, the GO trains were departing only about 1/3 full, and when the last train departed there were still thousands of people who hadn't reached the station yet. By some accounts it took over an hour to walk the 1.3 km from the stadium to the station, which is exactly what I'd expect with such large crowds. I find it insane that they decided to build the stadium so far from the station considering they force everyone to take transit and there's no reasonable walking route from Sheppard West, but that's a separate issue.
GO Transit claims that there are onward connections at Union for the Kitchener, Lakeshore East, Lakeshore West and Stouffville lines, but if you check the updated schedules the last Kitchener train still departs Union before the first train from the concert arrives.
Maybe if they actually scheduled extra connecting trains at Union they'd have an easier time convincing people to take the GO train at Downsview Park.
I know of no plans to add staging points to the Barrie line that would allow extra GO trains to be added, as happens at Union on major event nights.
There is a staging point on the Barrie line at the site of the former York U station. That's where two of the three extra GO trains are stored. My guess is the third train runs north in front of the 22:54 departure from Union and sits in the second track north of Snider diamond (the last southbound train has already passed at that point). They could potentially add more extra trains by storing them in the siding north of Maple.
