All,
Not that I would do it, there is not a problem of running your Neutral (AC term) or ground (a misnomer with AC) out and then back to the same lug on your transformer as it is the "same potential". Likewise with your Hot (AC Term) lead. Now this is for Lionel TMCC/Legacy setups. I am not into DCS but they tend to talk a spider leg approach and not a single buss (as opposed to a bus which is a multi passenger vehicle) around the layout.
Regarding running two Busses in opposite direction and terminating as I describe below, I am not sure of the merit. Running electricity through the track has the limitations of resistance through the track connectors and other forms of resistance due to the track. When you have resistance you have a voltage drop because of the inherent resistance of the track. Hence when you connect your power to the track near the transformer, your Locomotive runs fine at the point of power entrance and runs very slowly at the extreme distances from the power input point. Yes a buss wire also has resistance but it is infinitely small without a lecture on the formulae for calculation. But needles to say the gauge of the wire has a great deal to do with resistance of the wire. For my buss wires, both Hot and Nuetral, I use 14 gauge stranded. If you want less voltage drop then you can use 12 gauge but the affect of doing so unless you have a huge layout is of limited return for the additional cost of the wire.
Now as I said I don't think I would run it back to the same lug on the transformer. I ran my loop and then applied a crimped lug to the end and put a screw through the lug into wood just so it was not dangling.
Sorry for the verbose answer but I thought the extra verbiage was necessary based on some of the replies I read.
