Block signalling for mainline/industrial crossovers

[Anonymous]

I'm still in the planning/building phase, but I want to try to wire everything up right from the start.... so I have a question about how the prototype divides blocks on the main around industrial areas. Specifically, on my layout, I'll have two mainline crossovers in two separate areas. Actually, one will cross the main and the passing siding, and the in another area will cross just the main. So if I have a local switcher doing moves that will take him to the industry on the other side of the main, how do I 'protect' the crossing? Obviously the main will have to have two preceding signal blocks (one for an Approach signal and one for a Stop), but if the train on the main has already passed the first signal, and doesn't have time to stop for the second before crossing the crossover, how would the industrial switcher know there's an oncoming train? Will he have a signal on either side of the crossover giving a green or red signal? Or would he have to call the dispatcher for clearance each time he needed to cross? What's the normal prototypical practice? Regarding the wiring aspect of it, I have another question in the Layout Building forum regarding something else I want to try along the same lines as this, just doesn't qualify as a prototype question.

[ndbprr]

I don't think your scenario is any different from any other crossing. A tower either local or distant controls the signals. If you are modeling any time after the late 60's all trains would probably have radios and I suspect the industrial switcher waits every time for a clear signal. Before that time the industrial switcher probably had to contact the tower by lineside telephone.

[orsonroy]

In the rare case of an industrial siding crossing over a mainline, I'd suspect that there would be nothing more fancy than a telephone call box or a smashboard over the industrial tracks. The division timetable would have a notation that any switch job must stop at the crossing, call in to the dispatcher, and wait for clearance. They'd then be given a set amount of time to occupy the diamond (whether they were physically there or not) and perform their work.

A "smashboard" is basically a pipe gate that swings over the tracks, and locks into place. The local crew would stop, unlock the gate and swing it out of the way, move ahead, and close & lock the gate behind them.

Railroads wouldn't have wasted the money for a fully manned tower at this sort of site, nor would most spend the ca***o install fully interlocked signalling. Smashboards and a phone (or radoi these days) would be more than enough for the light traffic.

[Anonymous]

Sounds like I'll be radio'ing it in. I'm using a track plan for an industrial area based on one I found in a Kalmbach track plan book, and where I have crossings, they dropped the track under the main and had the main over a bridge. While the idea would work better overall, I prefer the crossings, and having the added challenge of working around mainline traffic. I've designed a double track concrete manufacturing/distribution plant that will see concrete covered hoppers out, and aggragate open hoppers in, but there's only a single track crossing so I'll most likely be fouling the main quite a bit as I move cars in and out. I like complexity, can you tell? lol And I just got a brain fart... I think when I play with the track plan again, I may design it as a complete double track main so I can run trains in both directions continuously.... Just a thought.

[ndbprr]

A couple of comments:
1. Inland Steel Co. in East Chicago, IN. has a track that goes from plant one to plant two under the four tracks of the old NYC and EJ&E and below water level in the Calumet River next door. When not in use by trains it is used by vehicular traffic and there are traffic lights at both ends. very steep entry and exit and a scary place to travel through. Did it once and won't do it again. fell much better goping around and watching trains. In adiition the IHB crosses all four tracks to access the yard serving Inland. The crossing is controlled from Hunt tower at the Calumet river about one mile west.
2. Whoever is second to the crossing pays for the tower and it crews even though it may be operated by the first railroad. So it is not inconcievable to consider the option if the industry was second.

[nobullchitbids]

I agree that a lightly trafficked crossing probably would use no more than a gate, which technically is not a "smashboard," and authorization by telephone or radio. If, however, the crossing is in CTC territory, a distant tower operator would be empowered to lock out the entire main for the time the switcher was authorized to foul it.

The question suggests, however, that the crossing is in a more heavily used area, since what was asked is how a railroad would prevent a false yellow or false green. The short answer is that a controlling tower has time-delay mechanisms built into its interlockings so that these false signals cannot occur. In other words, let us assume that we are concerned with protecting an eastbound hotshot proceeding through a plant with a north-south crossing which actually is interlocked and signaled, perhaps with dwarfs. The real railroad could handle this in a couple of ways:

1. It could stop all traffic through the plant, while the switcher was authorized to be there, by double-redding the main, then (and only then) clearing the switcher. To prevent the situation described, where the eastbound is upon its approach signal too late to stop at the next one, a time delay built into the interlocking prevents the switcher from being cleared until after the delay expires.

2. Obviously, because of the need for such delays, continually clearing the main, then the spur, then the main, &c., can lock up the plant for significant periods of time, during which neither direction can move. To avoid this problem, the prototype would use a "call-on" signal, which can be the third head down on the mast or a dwarf. The "call-on" would authorize the hotshot to proceed through the plant at dead slow, prepared to stop at the first sign of obstruction. A typical "call-on" indication is red-over-red-over-yellow on a mast or just yellow (or lunar white) on the dwarf (with red requiring full stop).

The prototype also typically would use additional devices to protect the crossing, such as interlocked derails keyed to insure that inappropriate cross-traffic went down on the ties long before it cornfielded in the diamond. It also might install (real) smashboards on the signals -- wooden slats obstructing the right-of-way on double- or triple-red and designed to break when any locomotive or car runs the red light (we KNOW you did it!).

Modeling a full interlocking is difficult but not impossible. I have done this using Wescott's Twin-T detector and the display system described in the October 1964 MR, with interlockings accomplished by grounding the DUs via the SPDTs of the switch machine or a DPDT on the panel for a crossing. Time delays can be installed by using a draining capacitor wired to transistors to keep the ground closed for a predetermined time, so that the entire plant will stay red for a realistic interval, and derails can be installed using switch machines activated by a transistor amplifier (it is important not to pull too much current through the DUs). The DU unit described in the article requires independent leads to the lamps, which can oblige an unsightly addition to a signal mast or bridge unit sporting multiple heads, so I poked around, looking for a DU where three of the lamps' leads were grounded, and I found one in a MR article written about a year or so earlier and designed by Howard Vogt. This looks promising, but I have not yet tried it and do believe it would need to be modified.

[billso]

An automatic interlocking is another common solution to this situation. An example was "NP Crossing" at Great Northern's Interbay Yard in Seattle. The NP ran parallel to the GN's main, and an industrial spur branched off and crossed the GN main and a couple GN yard tracks in order to reach Port of Seattle and Navy piers. There was no interlocking tower or operator. Signals were normally green for the GN main. When an NP crew wanted to cross they'd initiate a timer (either via a button or by throwing the switch, not sure which but both were found in this type of installation). The timer was interlocked with GN's signalling system. If there were no trains in approaching blocks the GN signals would go red, then the NP would get a clear signal once the timer ran down. The timer was in case a GN train got a red signal in its face just as it was approaching or passing the home block.

It's the same reason all railroad rulebooks require waiting 3-minute or 5-minutes after throwing any manual switch on the mainline. Gives an approaching train time to stop in the face of a sudden red signal.

--- Bill Sornsin

[MStLfan]

ndbprr,
Do you have pictures of the situation at Inland Steel? I am very curious about it.
greetings from Rotterdam in the Netherlands
Marc Immeker

[ndbprr]

Unfortunately I do not. It is a very complex area. CSX is the south most track followed by four CR(NYC) trackas followed by the EJ&E line to South Chicago. All tracks run east west and parallel from the Little Calumet River crossing about 1/2 mile west. The CSx track turns due south to go to an IHB yard and the IHB forms the other leg of the wye to cross all the other tracks and service the steel mill. The Inland track under it all starts parallel to all the otyhers insode the fence and turns once it is below grade. As I remember there are a couple of turns in the tunnel also before coming up parallel to the all the tracks on the other side. You should be able to see it all on Terraserver with an East Chicago search. Start with the river. LTV is on the west side and Inland Blast Furnace Row is on the right side and then go about 1/2 mile east.

[ndbprr]

http://terraserver.microsoft.com/image.aspx?T=1&S=10&Z=16&X=2313&Y=23059&W=1&qs=%7ceast+chicago%7cIN%7c

This URL will show you Inland Plant #2 on the north side of the tracks and Plant #1 is to the bottom. An IHB coal train is crossing all the tracks to the right into their yard. the yard in the picture is inside Inland steel co. The track under what appears to be catenary bridges in Plant #1 is where the track comes back up to ground level. Norm Bell

[MStLfan]

Thanks ndbprr, it looks fascinating to me.
But that tunnel could be scary indeed.

[ndbprr]

Now that I have been looking at it there are two entrances to the tunnel in Plant #1. the second one and the one you drive into is by the turntable a little further left and down from the picture right along the river so there must be a switch in there too. Thebiggest engine Inland uses is an SW heavily rebuilt so the turntable is more than adequate and I have never seen it used