[eternallyme]

Both of the main RIRO highways (11 and 35/115) are too congested anyway for them to be of any use these days. Even if they are only replaced by a 4-lane freeway, it would be quite valuable, although 11 from Barrie to Orillia would need to be 6 lanes right away.

I think the next widenings need to be to the east of the GTA, particularly from Kingston to Cobourg. The first place to start could be through Belleville (although the fact that there are three interchanges in close proximity warrants a design change), and through Trenton (there are three interchanges not as close but traffic increases somewhat).

Through Belleville, there are two choices: an 8-lane cross section around the Highway 62 and 37 interchanges (to help with the weaving) or a 10-lane cross section with C-D roads (3+2 on each side) to serve the two interchanges. That requires new bridges on the Moira River but would isolate the weaving from the through traffic completely. Through Trenton, a normal 6-lane cross-section would be sufficient though.

After those are done, the gaps can be filled in for a continuous 6-lane corridor from Kingston to Cobourg (and 6+ lanes from at least west of London, perhaps Windsor, all the way to Kingston).