Give this a thought
As a 2-way radio shop, and though I dont have any RR customers (class 1 all have their own radio techs), I still keep up on what other industries are doing. The FCC narrowband mandate required railroads to tune their radios to use less bandwidth so they could have more channels available (something they dont need) but also so co-channel interference would be reduced (something they did need). This mandate also affected all Part 90 Land Mobile radio users operating on frequencies between 150-174mHz, and 450-512mHz, including Police and Fire departments, farmers, taxi companies, warehouses, etc.
Many of the radios in use by railroads during the transition time leading up to the switch were so old they didnt have they narrowband option built in, which meant a large number of their radios needed replaced. While the mandate only required a switch from wideband Analog to narrowband Analog, many businesses and public safety agencies saw the added benefit to switching straight from wideband analog to digital. The AAR (Association of American Railroads), in trying to forward think to possible future changes, recommended that member railroads upgrade to radios that can work on both narrowband analog AND digital channels, all done through programming of the individual radio. The difference in price between an analog only radio, and one that will do both is not that much.
Also, railroads had to modify their FCC licenses to permit the narrowband operation, and knowing that someday in the future they could decide to switch to digital, many modified their license to permit digital as well.
The benefits to class 1 railroads to switch to digital is:
Better audio (normal FM has static when a signal is weak; digital has no static, if the radio can hear even a smudge of the weak signal, the audio is nearly crystal clear)
Better co-channel interference rejection
Data can be sent over the voice channels (think about track warrants, permits, or bulletins being digitally transmitted over the air to train crews to a computer display, without any additional data infrastructure, or LTE network).
Look at the track record of the FCC over the last 40-50 years. Wideband used to be REALLY wide band! Then newer technology permitted narrower transmissions. By the 1980's, it was made even narrower, and by late 1990's "narrowband" started becoming the way to pack more channels into a smaller spectrum. We are a RF spectrum hungry society, and as time goes on we will need more efficient radios to allow more users to use the same amount of RF space. The only way to do that is now with digital modulation.
To the OPs original concern. The digital mode that railroads have adopted is call NXDN. I have heard some encrypted NXDN transmissions is a few big cities around the midwest. Most likely these were RR police agents, but of course I couldnt know for sure. I do know railroads have been testing NXDN in yards and on road channels, but are probably several years away from daily road channel use. If I had to guess based on things Ive heard or read, CSX is the closest to rolling out digital on a road channel. I have an NXDN radio ( I have my own radio shop, remember 
, and love it. But a normal consumer grade scanner Im sure would suit you just fine for now. Then if you start hearing the digital hash noise on railroad channels, it might be time to upgrade yourself.
Good luck
Steven
