Thanks, Lakche, for the link to the MTO stuff; it is helping me figure out why the Cyrville Road Bridge is being designed the way it is.
At the Open House, I was curious to see that the bridge was being lengthened only over the east-bound side of the 417/OR174. There will be space for an extra, future, lane as they move that abutment south, but the piers in the bridge center are to remain in the same location (which is reasonable since they are in the median of the 417/OR174) and the north piers are to replace the north abutment – in the same location. Thus, there will not be any extra room to add an additional west-bound lane in the future. A new abutment will be added to the north, creating a third span, but it is only to bridge the new extended St. Laurent off-ramp.
To illustrate this issue:
The critical points are the yellow notes: The distance between the central piers and the new north piers will be the same as the current distance from the central piers to the north abutment; this will only allow the current 2x OR174 + 2x 417 lanes.
The City could widen the 174 to 10-lanes in each direction, but the MTO is only allowing two lanes to enter the 417. ‘The Split’ will forever-more be a bottle-neck from the east. This is the MTO plan – basically throttle the flow from the OR174 so that the 417 only needs 4 west-bound lanes.