The IC generally used 161.190 on the mainline from Chicago to New Orleans and 160.920 on branches and secondary lines, like the Iowa Division and the lines to Springfield.
The former ICG/Alton Route line thru Logan County (the one along I-55) uses 161.280. It is currently owned by UP but most of the trains that run on it are Amtrak, there is only a peddler freight or two that run on it on a regular basis.