TTC operates some bus routes for other agencies(you probably know a few already), but the other agencies don't operate buses for TTC. For example, once a TTC bus goes into Mississauga, it is now a Miway bus. On the other hand, Miway buses go into Toronto because not because they want to serve residents there but because they need to connect to the subway, and so they do not serve TTC riders(a Miway bus heading to Islington can't pick up riders in Toronto, and a Miway bus returning can't drop off passengers in Toronto).
I referred to this kind of situation as being similar to cabotage rules.
For those who don't know what I mean when I speak of cabotage, in the traditional since, it usually refers to transportation of goods or passengers between two points in country A while the transport operator is in country B.
Cabotage rules are the reason for instance why United Airlines can't run a flight from Pearson to Montreal.
Similarly, cross border trucking works the same way, if I was a trucker, I can't move anything between two points within the US. I could pick up a load in Mississauga and have multiple drop offs of the same load at different points in the US, like suppose I drop half the load off in Detroit and the other half off in Chicago. Under no circumstances could I bring a load from Detroit to Chicago. On the way back I could indeed have multiple pickups, but these pickups must be headed for Canada, I can't again pick something up in Chicago and drop it off in Detroit, but I could in theory pick something up in Chicago and pick more stuff up in Detroit as long as it's headed to Canada.
The idea is the same with passengers, Qantas runs a flight from New York JFK to Sydney with a stopover in LAX. One cannot buy a ticket for the NY to LA portion of that trip because it violates cabotage. On the way to Sydney, the plane can pick up more passengers in LA but NO ONE can get off in LA, similarly on the return trip, passengers can be dropped off in LA but no new passengers may board to go to NYC.
This is also why the Amtrak run from NY to Toronto runs as a VIA train on the Canadian portion of the trip, with a Canadian crew, because of the multiple stops, unlike the Amtrak routes into Montreal or Vancouver where those places are the ONLY Canadian stops on the route, thus the American Amtrak crew stays onboard to Montreal and Vancouver.
I know it's different, but how MiWay and YRT (and possibly Brampton) behave when they enter Toronto mirrors the cabotage rules. Oddly enough, the TTC doesn't have any routes other than the 192 Airpirt which follow "cabotage rules" into the suburbs, I mean, the 58 Malton could easily operate as the only non Toronto stop being the Westwood Mall, or perhaps a hypothetical route to Vaughan Mills which followed similar "cabotage" restrictions. In the hypothetical 58 Malton scenario, only one fare would be paid at the Westwood Mall and the bus would go directly into Toronto's boundary before its first passenger could be discharged.
