Midtown Urbanist
Superstar
There are many options for Don Mills, besides tunneling.Maybe when the DRL crosses the Don River at Millwood, it should stay elevated to Seneca College.
That's about 14km. The difference between $400M/km for underground vs. $125M/km for elevated amounts to $3.5B.
This is likely the option of choosing between extension to Eglinton, or extension to Finch+.
Similar thing happened in the West end. If the Spadina line would not have been built in the median of Allen, it would likely still be terminated at Eglinton today.
We can cut-and-cover, we can elevate, heck we can even have it trenched.
I have the feeling the only option that would be studied is tunneled however.