You'll generally want to aboid looping your bus on itself, especially with DCC. The primary reason is that doing so can potentially corrupt the DCC signal, especially for longer loops. Think of a DCC signal (basically an electrical pulse) leaving the command station and traveling simultaneously along both sides of the loop. Now if a decoder is anywhere along that loop other than at the exact furthest point, it'll actually receive the same DCC signal (i.e. command) twice, but at slightly different times. Once over the shorter side of the loop, and again over the longer side, a minute fraction of time later. The longer the loop, the longer the fraction of time, the higher the chance that the DCC pulse will step on itself and one or more zeroes will turn into ones or viceversa, corrupting the signal.
