Jonathan,
Thank you for the link to the picture but, being probably very think headed, there is still something I don't understand. It seems to me that a locomotive coming from the bottom of the pic and the track curing to the left it's momentum no matter how slow it may be going will cause it to stay aligned on the right hand rail thus causing it to bypass the frog and stay on the right rail causing a NG loco to come off the inner of the three. (Sorry about the long sentence)
What am I missing? If this were true then a Mudhen would be truyly living up to it's name.