If I had to guess the gap is for future expansion!
The transition from a 1910 concrete and steel viaduct to a modern steel structure is a delicate affair. Figuring the 1910 viaduct has had 111 years to settle in its ways, where a brash young upstart steel and concrete pillar will be wiggling around for a bit. A hard tie together would cause an issue for one-or-the-other or both of them.
By leaving a gap and most likely a forgiving connection should lead to harmony in there spatial relationship. When the trackage is laid there will probably be a rail expansion joint at that location.
Here are some photos I took on Friday, January 15, 2021. As you can see the new and the old will not be hard tied together.
Or, someone measured wrong!
Member of IEEE, BSRA, ERA, CERA, SLIHS, BERA, NRHS, NRHS Wisconsin, SPH&TS, SFRH&MS, RGM&HS, UPHS, NHRHTA, NE PRRT&HS and PRRT&HS
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