... case, locomotive wheels are wider than wagon wheels. If the raised portion is set to suit locomotive wheels it will have no effect on wagon wheels. If it is set to suit wagon wheels, locomotive wheels would jam on it. That's why self-guarding frogs are not used in the UK. I must confess that this extra check rail is invisible to me. If derailments frequently occur at the entry to a switch, this would be controlled by means of a conventional check rail. Here's an example of that: 2_150732_540000000.jpg Pic thanks to Adrian Marks of this parish, originally posted on RMweb, see: http://www.rmweb.co.uk/forum/viewtopic.php?p =129570#p129570 regards, Martin. posted: 15 Nov 2014 17:31 from: DerekStuart Simon I know what you mean about the other rail- there is a protrusion about parallel with the "lower" end of the mystery rail. But I don't think it's a second checkrail. The example Martin shows is of course inside and you can understand its purpose. I ...