Sorry for the double post but to get back on topic, it looks like crews are finally working on the second bridge on Wells-Wentworth, this time under the Freeport Sub track.
For the first bridge below the St Charles Air Line, the railroads were willing to re-route all trains for months so the bridge could be built without active rail traffic. However, this is not the case for the Freeport Sub. Since freight trains and potentially Amtrak will need to operate continuously, crews are building a temporary "shoofly" bridge that will allow them to excavate around and underneath the track even as trains pass overhead.
Bridge spans for the shoofly:
Site is prepped for bridge installation:
Steel piles driven between/around the tracks to support the bridge spans: