Diamond crossing protection - any particular method?

[jhugart]

While readig in Model Railroad Planning for Realistic Operation, I noted a statement about crossings: Apparently, unless they have the right kind of signalling system, trains are required to come to a full stop before proceeding across (kind of like a 4-way stop sign).

The right kind of signalling wasn't explained, but it did mention that the junior railroad (presumably, that means the one which built the second, crossing track over the existing ROW) bears the responsibility in perpetuity for managing the crossing.

How exactly does this work in practice? What happens when a road crosses its own line?

[CSSHEGEWISCH]

The signals involved at a crossing are interlocking, it is impossible to clear more than one train at a time over a given stretch of track. If no route selection is involved, the interlocking may be unmanned and automated.

Probably the best-known non-interlocked crossing is Brighton Park in Chicago. All trains must come to a complete stop (required by state statute) and be flagged through the crossing by a watchman posted there.

[tomikawaTT]

Very old (1880 on) practice was to have a gate-type signal that could be swung across either one of the tracks at a crossing. It was usually across the track of the junior road and could only be moved by someone who had switch keys. If a junior road train needed to use the crossing, the train would stop, the head-end brakeman would unlock the gate, swing it across the track of the senior road, then lock it in place. The train would have to stop (or proceed at less than walking speed) to allow the rear-end brakeman to restore the gate to its original position before the train could proceed. Senior road trains would not have to stop unless there was a junior road train actually occupying the diamond.

Later, the same idea was behind the 'smashboard,' kind of a cross between a crossing gate and a semaphore signal. If somebody overran a smashboard, the evidence would be scattered all over the right-of-way.

Busy crossings were among the first facilities to be fitted with interlocking. Originally rod-connected hand (forearm, upper body and leg) operated levers moved signals and (if present) turnout points, working through an arrangement of sliding bars and dogs which permitted only one signal at a time to show anything but absolute stop. Later the workings were converted to electrical operation, then CTC. The basic rule remains, at a signal-equipped crossing, only one signal at a time can be cleared. At a totally unsignalled crossing, the train must be brought to a full stop and a man must be placed on the ground to indicate, by flag or lantern signal, that it is safe to proceed.

One midwest state, with technologically-challenged legislators, actually passed a law which read, "If two trains arrive simultaneously at a place where their tracks cross one another, neither may proceed until the other is completely out of sight."

[tjsmrinfo]

also at diamonds there may be an interlocking tower along with signals FACING the direction of travel on all 4 sides, so a single main North-South line will have a signal on the engineers side facing north for a southbound.

a signal facing south for a northbound etc. i'll try to find some pics either prototype or model to post here.

hope this helps


tom

[dknelson]

Here is a smashboard evidently in current use.
http://www.rrpicturearchives.net/showPicture.aspx?id=15511

Dave Nelson

[CSSHEGEWISCH]

Smashboards are relatively rare and have generally been used to protect movable bridges.

[wjstix]

An interlocking signal also looks different from a regular block signal in that it has at least two heads, one above the other. In the case of a diamond crossing, one head would be a "dummy" head which would only show one aspect - red. The other would at least be able to show green or red. Usually the dummy would be the lower head, so the signal could show clear (green over red) or stop (red over red).

A two headed signals are used to avoid confusion with single head block signals, which (depending on the railroad etc.) are often "permissive", meaning a train can proceed thru the red signal slowly prepared to stop. An interlocking signal is "absolute" meaning you have to stop and not go past the signal until you are given a clear signal.

[jimrice4449]

Actually absolute signals are marked by not having a number plate, at least that's been the case on all three RRs I've worked on. I know of at least one interlocked Jct (Battleground where the SP & GN crossed just south of Klamath Falls) that had four single head semaphores protecting the jct. Generally an absolute semaphore will also have a different shaped or colored blade than a regular block signal. The confusion over multiple heads migh be because they're also used to indicate track aligned for a divergent route.

[wjstix]

I guess the bottom line would be to research the railroad you're modelling, or if you're freelancing, research the prototype railroads in the area you're modelling to see how they handle it. Each railroad had it 's own rulebook which covered things like this - how signals are identified as far as permissive or absolute etc.

I would say that a two (or three) headed signal, with all the signals lined up one above the other, is ALWAYS an interlocking signal and not a block signal, but that a signal with one head is USUALLY a block signal - but could be an interlocking signal, depending on location, the railroad that erected it, markings on it, and so on.

(I think too, in recent years, with radio and remote dispatching etc. that more interlockings are controlled with single headed signals than would be the case years ago.)

[csxengineer98]

none of you touched apon something i have seen at a dimond...
a STOP sign...just like a 4 way intersection... but for railroad tracks.. i saw it outside of youngstown OH..on a little industral branch that is unsignaled.. it basily has a sign that reads STOP at the clearnece for each direction of traval... so.a train comes up.. stops..and if the way is clear...they go...
csx engineer

[Anonymous]

I actually saw one of these used when I was a teenager at a rural diamond at Maxwellborn. Alabama. The main was the Seaboard it ran on through to Atlanta), and Southern was the branch line (ended a few miles up the road in Piedmont, AL). Late one afternoon, I was out for a drive, and saw the Southern local coming up the line. A crewman got off the train, unlocked a control box, and pushed a button. He had to wait for a bit, then the gate unlocked to where it swung 90 degrees to unblock the Southern and block the Seaboard. They pulled past, then reversed the process on the other side. There were two 90 degree gates either side of the diamond to block both sides, if memory serves me right. I may have a picture buried somewhere. Both lines are long gone now.

Years later, an in-law who worked for Southern gave me a timetable, and in it was the procedure for this crossing. The main thing was that there was a safety timer to ensure the gates could not be opened until the other line was sure to be clear, as well as a lockout on the blocks either side of the diamond to not allow the gates to swing until clear.