One major consideration is that the reverse section controlled by the AR1 must be longer than the longest train.
It is a common misconception that the AR1 will work with an analog controlled ("DC") locomotive; it will not.
The AR1 is meant to be used only in a DCC enviroment. The AR1 coordinates the phasing of the reversing section with that of the mainline (non-reversing) section of the layout. Because a Digitrax layout can be a complex enviroment with detection and transponding, etc. consult the approriate Digitrax user manuals and the Digitrax Tech Support Depot knowledge base.