With all due respect, I understand what you're trying to say, but many drivers that park at Finch Station don't use Yonge Street to get there. To distill future or even existing numbers based on Bus Ridership and vehicles along Yonge Proper doesn't give the full picture. The catchment at Finch Station extends to Bathurst and Bayview vehicles that come south and use Hilda, Willodale and Finch to get there along with Yonge Street. Even despite this, not all vehicles on Yonge or any other corridor are all destined for Finch Station either.
For day one numbers, there isn't a large area that you can based numbers on and becomes a guessing game as how many new riders would use the new line that day or week.
As for car numbers, its a guessing game unless you run every plate through the system to find out where they live. How many of those car currently using the Finch lots is unknown by me and I chose the high number. Some could be for local business since it could be cheaper to use TTC lots than other places.
Over time for future number, you can arrive at X numbers assuming a lot of things.
Other than World on Yonge, nothing has been built between Steeles and RHC to add numbers to ridership numbers based on old data. You can add new data for hwy 7 and north Yonge.
The number I used for opening day is based on the time frame that the line was supposed to open and is out of date since we have no idea when the line will open today. At the same time, how long does it take to get development off the ground to meet future demands??
There is more development north of RHC today than south to the point it reinforce the need to take the line north of RHC when the line gets built. There is a lot more development on Hwy 7 than before, with a good chunk using the GO Stouffville Line than the Yonge Line.
In fact I did a 30 year outlook for both Hurontario and Yonge and it was only around 25 that Yonge ridership pass Hurontario given the fact it has less area to build density. The last time I did ridership numbers some years ago, Hurontario was still beating Yonge Numbers 2:1 and it only getting an LRT. The Yonge number was based on 8% growth yearly.
The Town of Richmond Hill wants a tunnel for transit through the downtown area, since Yonge will not handle transit like it should and will be a lot slower than it is today due to increase in traffic.