Eastern Railroad Discussion > UP/CSX question at St. Elmo Illinois

I went train watching with a friend today and we stopped in St. Elmo, Illinois. We watched two UP stacks trains exit the CSX to go south. However, right close to where the double main lines go back to single track, there was a siding (or line)that veered off to the north off the north main. Any idea on what that line is/was?

If I interpret your description correctly you are referring to the former CEI main. After crossing the PRR double track at St. Elmo, the CEI swung east and paralleled the Pennsy for 5 miles to Altamont, where it then swung north towards Chicago. When the run through service between CR and MP was established in the early 80's, the capital improvements that you saw were made. The two CR tracks and the CEI track were reconfigured into a three track corridor under the control of the CR dispatcher to facilitate the interchange of trains and for a time being, crew change, until the labor agreements were in place for the CR crews to run into Salem. One caveat, it's been a long time since I've been to St. Elmo, things could have changed.

The tracks there (S to N) are known as the Single Main, South Controlled Siding, and North Controlled Siding. UP crews must carry CSX bulletins for that little stretch of track, and their trains are called by their CSX Z number scheme. Z is for foreign trains.