By the time a southbound YUS subway train gets to Eglinton during crush hour, it's already packed. The Crosstown is going to make that situation much, much worse. Without removing some of the load further down the line, people transferring from the BD line could be waiting 5 or more cars just to get on. A DRL (Don Mills/Eglinton plan) would take a lot of the load off the Crosstown and YUS from commuters intending to get to the core. All the people in the new development in Leaside could take a short trip *East* to a subway they wouldn't need to transfer from in order to get downtown. The Crosstown would be in a better position to serve its intended purpose as a northern east-west corridor, rather than just another feeder for the YUS.
There are two factors to consider.
Do enough people coming south on Yonge get off at Bloor to open up space for people coming west on the B-D to get on. This relies on a whole bunch of people getting off Yonge at Bloor, and then a whole bunch of people getting onto Yonge from Bloor. This will have a much worse dwell time at the Y-B station and thus the capacity of Yonge will drop.
OR
Does balancing out the transfers at 2 stations (instead of all transfers at one station) allow for shorter dwell time at Y-B, which will allow more trains through and increase capacity on the Yonge line.
Roughly 25 to 30 trains per hour use Yonge. This is about a 130 second frequency. For every 5 seconds that the critical station dwell time can be reduced, one extra train can fit on the Yonge line (5 seconds x 27.5 trains = 137 seconds). Each train is an extra 1000 passengers - probably more with the new trains.
Looking at the
DRTES (Exhibit 4-3) in 2031, with the Yonge extension (and Eglinton in-median LRT), there will be 34,000 passengers coming south approaching Bloor. South of Bloor, there will be 39,200 passengers. Thus, the capacity of the line will be 39,200. If you can get half of the 9,200 WB to SB passengers (say 4,000) to transfer at Eglinton instead of Y-B, then there will be 38,000 passengers coming south approaching Bloor and the 39,200 south of Bloor. But because there are 4,000 fewer passengers transfering on at Y-B, the dwell can be reduced by 5 or 10 seconds and the capacity of the line would go up by 2 or 3 thousand to 41,500. I do not have all the numbers available to me (the Y-E station needs to be designed for the required number of transfers - but since it is a centre platform it should be easy enough to add side platforms and have a Spanish 3 platform solution), but it looks like the convenient Eglinton line would have the Yonge subway at 92% capacity (38,000 / 41,500) just north of Bloor and 94% capacity (39,200 / 41,500)just south of Bloor. The inconvenient median LRT on Eglinton would have the Yonge subway at 87% capacity (34,000 / 39,000) just north of Bloor and 100% capacity (39,000 / 39,000) just south of Bloor.
Which one is better - the one at capacity for 1 km south of Bloor, or the one that is close to capacity for maybe 5 km.
In the above, some passengers may continue on Eglinton to Spadina and transfer there. Thus, if Yonge starts getting close to capacity, there is a relief valve. With the less convenient in-median LRT, all passengers would be taking B-D and there is no such redundancy. Once the DRL gets built to Eglinton, this will no longer be as big a concern since Eglinton riders would transfer to the DRL instead of taking the Yonge line.