Fun fact: The SRT today moves 39,000 per day. The Scarborough Subway is projected to move 31,000. That's a 21% drop in ridership compared to the SRT
All this expenditure, to lose eight thousand riders.
Anyone care to explain how this subway extension will be so wonderful for the 20% of SRT riders who will be displaced from rapid transit?
That's surprising indeed. Do you have the source? In such puzzling cases, I usually try to look at the source with detailed numbers, confirm that they are correct in the first place, and then try to understand the cause(s).
I can think of the following reasons:
1) Some riders might shift to SmartTrack / RER. Those riders would be lost to SRT as well.
2) Loss of the Lawrence East station; that could account for a few thousand daily riders.
Loss of the Ellesmere, Midland, and McCowan stations is hardly relevant for the total riders count, as all those buses will feed into STC.
Loss of riders travelling between stations other than Kennedy should not matter much, as the number of such riders is very small.
On the other hand:
a) The projected peak ridership for SSE, even the latest and lowest projection of 7,300 pphpd, is higher than that for SRT (5,000 or 5,500). The total daily ridership and the peak ridership aren't always proportional, but usually they correlate for routes of similar length.
b) We know that SRT is unable to carry all rush-hour riders that want to use it, and therefore TTC has to run a parallel express bus, 131E. When the subway opens, obviously those riders will switch to subway.
c) Substantial residential growth and some employment growth is expected at STC by the time the subway opens; that should add a few thousand riders.
d) Natural growth occurs everywhere in the city, and some of it will occur in Scarborough in places other than STC. That should add some riders to the bus routes that feed into STC, and a large portion of those riders will transfer to the subway.
So, if you are saying that factors (1) and (2) overweight factors (a) to (d), I can't assume that it is "wrong" without having access to the source, but I can say that I am puzzled.