When Hornby Dublo introduced their 00 scale three rail system, one of the features exploited on their recommended layouts was the simple ability to reverse the direction of a train without the involvement of electrical switching, only track. Remember with this system, forward is always forward on the line controller. If you pick up and turn around a locomotive and then reapply power in the same direction, the locomotive will run in the opposite direction to before, in fact just as DCC systems do now.
It is quite possible to have reversing loops on two rail layouts, but it does require the use of correctly located single rail gaps and a bit of wiring. The first one requires one point, dead or alive and a turn back loop. Attached to the point a single changeover accessory switch requires to be fitted. Trains may be run around the loop in either direction depending on the setting of the point but must be stopped in the turn back loop for the point to be changed and the direction switch on the line controller to be reversed. Gaps should be located as shown and the three wires installed as on the diagram.
That's not the only way to do it. If you only have set track points, again dead or alive, without the facility of fitting an accessory switch, don't despair, there is a solution. Once again the gaps are located as shown but this time across each gap is fitted a diode, installed in the direction as shown. This solid state device conducts electricity in one direction only. As diodes are directional the slight drawback to this system is that trains can only be run around the turn back loop in one direction only. As a plus though, no wiring is required. Because of the use of diodes, it is imperative that your locomotives operate in the correct direction as mentioned in Short Circuits No. 1. The third option shows a reversing loop installed in a traditional oval continuous run layout. With the wiring shown, the reversing loop can be used but it is required that the train is stopped in the cross loop whilst the relevant points are changed and the direction switch on the line controller is reversed.
There you are, three ways to turn back.