You might do better listening to the closest yard frequencies. Often (not always), yard operations use a repeater which might be easier for you to hear. Check the listings.
Better yet, just set the scanner to search 160.215 to 161.565 MHz in 15 kHz steps. It's always possible that there's stuff out there which isn't in the database, so If anything is there to be heard that will probably be the best way to find it. Alternatively, as JoshuaHufford suggested, program the basic 97 AAR frequencies in a bank all by themselves and start scanning. The AAR channels are listed on the Nationwide page under Railroads.
The advantage to programming the individual frequencies is that you can put them in a bank using the corresponding AAR channel numbers, for example (using the first bank) channel 07 would be 160.215, channel 08 would be 160.230, channel 72 would be 161.190, and so on. This makes it very easy to recall a frequency quickly (if you hear someone say "go to 14" all you have to do is hit MAN 1 4 MAN and you're there).
If you're using a computer to program the radio either way will work, but if you're doing it by hand, the search method is probably a bit faster than entering 97 frequencies by hand.