I know it sounds dangerous, but, haven't anyone thought of electrifying by just using the two rails as conductors, one rail per pole? So no need of third rail o

I know it sounds dangerous, but, haven't anyone thought of electrifying by just using the two rails as conductors, one rail per pole? So no need of third rail or catenary. I suppose the expense would be isolating all the axels! This is the method used by model railroads by the way.