Why did some of the early model train manufacturers use three rails? Lionel, Marx, and Marklin used a center rail. Why? Prototype railroads don't have a center rail. Or did some of them have that? Well....
So a look into early model trains and motor technology reveals the answer. Early electric motors were often AC motors. And while later DC motors were the norm, in. 1910 such was not the case. And for several good reasons. But this opens up a problem in track design. when a train goes around a reversing section of track the polarity changes. With DC motors this is a simple fix using two DC reversing switches. But in AC the direction of the train is determined not by track polarity but by the polarity of the coil magnets in the motor. I early models this required a switch on the locomotive. Later a relay in the locomotive could reverse the direction but the AC current at the track stayed the same. So the easy fix was to run the hot leg of the AC current through a center rail and the neutral at both outside rails. Problem solved. But at the expense of a realistic track. But as these were toy trains, it didn't seem to matter. Until later when people wanted a better-looking track.