This is North America. ATC has been around since the 1960's, but outside of North America. ATC is only a relative newcomer in North America.
Same with high speed or bullet trains, still waiting for that. Can't have high speed trains when there are level crossings. We have too many level crossings in North America.
Er, not sure how level crossings and bullet trains are remotely relevant.
Anyway, I looked it up and since 1960, there have been 8 new-build grade-separated metro systems in North America: Montreal (1966), SF BART (1972), Washington (1976), Atlanta (1979), Baltimore (1983), Miami (1984), Vancouver (1985) and LA (1993). All 8 have had some flavour of communications-based train control system from the start --- different degrees of automation and human operation, absolutely, but somewhere on the spectrum beyond 100% human beings looking at coloured lights. I don't know why certain posters feel the need to simply make their own facts up other than it giving them a chance to make a flippant remark.
Obviously, when building extensions onto an existing, older, metro system, there are good reasons you're less likely to see ATC pop up that probably apply everywhere in the world -- both technical reasons (commonality of fleet and signal systems and staff training) and political reasons (less likely to get automation in place when there's an existing train operators union).
But in any event, what I'm saying is that in 1995 ATC was a mature technology, well-known to transit professionals in Toronto, and was certainly a viable option for Sheppard.
Can anyone who was following the transit debates of the day recall whether there was any thought given to ATC or was it just taken as a given that slightly newer versions of the 1950s glowing lights would be installed in the tunnels?