In the document ( https://www.toronto.ca/legdocs/mmis/2022/ie/bgrd/backgroundfile-225843.pdf ) that justifies the cost increases for the engineering firm, the part that concerns me is this:
In February 2022, at the 90% review stage, Canadian Pacific Railway requested the City change the bridge superstructure type to one that maximizes flexibility for the railway's future operational needs, rather than limiting their ability to re-align tracks at this crossing with a through plate girder design.
Does this mean that CPR wants to add some additional capability (tracks and traffic) to the bridge? There was already a design change in 2014 to add an additional track for Metrolinx.
Not necessary capability or capacity per se.
The original design would have required all tracks to be parallel to each other, as the plate girders providing structural support would stick up past the top of the rail. By changing the design to one where all of the structural elements are below the track level, tracks can be installed at any angle CP feels that they require, or even allow them to place switches on the bridge.
Also of note, according to this document, the TTC is no longer requesting provisions for streetcar tracks.
The City issued a Request for Proposal for the detailed engineering design of the new bridge, including provisions for dedicated streetcar tracks in 2011. This Request for Proposal was retracted upon confirmation from the Toronto Transit Commission that there were no longer plans for future streetcars at this location.
This only slightly affects the design of the bridge as a whole. The slab that ties the bridge footings below the road can be made thinner and installed closer to the surface of the ground.