by AndyW » Wed Nov 20, 2019 9:54 am
Hope you don't mind me tagging onto this thread as my first post. I'm a Brit who's been watching the Fostoria railcams quite a bit over the last few weeks, partly because it's a busy location and partly because there are signals in view.
I'm fairly new to US signalling practise, and although I've done some background reading it's always interesting to see the reality on the ground. Like the original poster I've also seen red over lunar at the CSX/NS diamond for a westbound train which was close behind another one. I assume the route has already been set for the second train and the signalling system is clearing the signals in rear of the first train automatically as that train clears the blocks ahead.
With this in mind I'm curious about how far the first train must go before the signal in rear will clear to red over lunar? Obviously for yellow over red the first train must clear the whole block ahead, but how does it work for red over lunar?
I also have a second question, which might relate to the first one. Does US signalling have the concept of what in Britain we'd call an "overlap"? In other words does the whole of a train not just have to clear a signal before a second train is allowed to approach that signal, but the first train have to clear a specific distance *beyond* a signal before a second train is allowed to approach that signal?
Part of the reason I ask this is because the westbound signals at the CSX/NS diamond seem pretty close to the actual crossing itself, and thus there doesn't seem to be much distance (or overlap) between the signals themselves and what we'd call the "fouling point", i.e. the point at which a train slipping past a red signal could potentially cause a collision. I've not actually seen a train approach any of the westbound signals at red, so I'm wondering whether this is even allowed at Fostoria?
And are the numerous road crossings a factor in the signalling design here, i.e. would the system be designed to hold trains further back rather than have them stand near the junction and block the road(s) for some unpredictable amount of time?