With the introduction of the FCC narrowbanding requirements in 2013, the American Association of Railroads AAR) has officially adopted the NXDN digital standard for future endeavours.  As a result, in the coming years many railroads will begin the migration to this mode, primarily for secondary operations.  The common road channels will likely remain analog for sometime to come; however, these analog frequencies have also become subject of the FCC narrowbanding mandate in order to make room for the additional channels required for digital operations.  The original AAR channels 07-97 have been converted from analog FM 15.0 kHz channel spacing to narrowband analog FM (a.k.a. NFM) 7.5 kHz channel spacing and renamed the channels to 007-097.  This change allowed for the creation of AAR channels 107-197, which also share the 7.5 kHz channel spacing and AAR channels 307-497, which are 6.25 kHz spacing.  Both groups of channels fit in between the original AAR channels of 007-097.  AAR channels 107-197 can be utilized for either analog or digital operations whereas AAR channels 307-497 are digital only operations; however, the AAR has recommended that railroads continue to utilize AAR channels 007-097 in analog for common road operation and to not utilize channels 107-197 and rather migrate directly to using the newer NXDN digital format on channels 307-487 for secondary operations.  AAR has also set the standard NXDN digital operation mode to what is known as "NXDN-VN" or "Very Narrow" or "NXDN 4800" using the 6.25 kHz spacing.