It's surprising when you realize just how late in history it was still a pain in the ass trying to cross the Don Valley. In 1958, north of Bloor, there would have been, what... Laird? Some little street down in the valley called Park Road that really didn't go anywhere (and might have been out of action after Hazel; not sure), a one lane bridge at Pottery Road, a bridge not much wider at Don Mills Road, Eglinton Extension probably just freshly opened, a windy road down and back to a one-lane bridge at Lawrence. It wasn't till you got up to around York Mills and the valley got shallower that it the bridges got more reliable. That's in the east... The West Don's a different story because a lot of its crossings seem to be north-south and for some reason, York County and Metro took those more seriously. It's like nobody cared about Scarborough.
Ah... I think I've hit the nail on the head.