Wouldn't it be more useful to add another E/W line if ever OL is at capacity... say on College?The difference is that the OL will be able to reach 90 second frequencies and the TR tech will only be able to do 120.
30k PPHD is also not a low capacity line, at all. It's much higher than what line 1 delivers in terms of capacity today. It's just not what a TR train can achieve when fully maxed out, which is very, very high capacity.
For the OL to overload at 30k PPHD it would have to be in the top 3 busiest subway lines on the continent. It's a ton of capacity.
The question isn't if the TR could deliver more passenger space, it obviously can, it's a question of scaling the build to what is actually realistically needed. Metrolinx could just as easily spec the line out to accommodate 200m long OL metro trains and be able to run the line at 60,000 PPHD - but why would it need to? The line will be at 50% of design capacity at opening day. It's not a binary choice, it's choosing a level of capacity that's actually needed. There is a reason Metrolinx isn't even planning on running 100m trains for the first 20-30 years.
Many here seem to think that they should be building the line with TR trains for the additional capacity, but it's not really needed. And that's the whole point of this discussion, building that extra capacity would increase project costs massively for capacity that won't be required, maybe, until 2 generations from now. There are simply too many variables between then and now for that to be an assured investment.