The link below takes you the RR database for ILL Railroad freqs local to Chicago. Amtrak operations are specifically 160.305 (Gates) at Union Station. There are I believe, two listed Police Mobile freqs that are no longer operational. I think these were either mobile extenders or stationary repeaters. Amtrak, BNSF, and all of the other railroads that are alive and have police or "special agents" (just a fancy word for that railroad company's police) all share the same nationwide frequency.
Railroads / Metra Scanner Frequencies and Radio Frequency Reference
Amtrak Police
Linear Mode
