Philosophy #1: Full route flexibility, but two trains cannot share the center control point (CP) track. Photo shot by BNSF’s (AT&SF’s) CP CAJON (M.P. 62.8) in Cajon Pass, California.
Philosophy #2: In a full eight switch arrangement, two trains can traverse portions of the center track, but routing flexibility is limited. Photo shot at UP’s CP B182 HIGHWAY 10 (which highway crosses Highway 30 that follows the tracks) on UP’s Central Corridor triple-track line in Nebraska. The reverse counterpart crossovers are immediately behind the camera.
In all fairness, UP in Nebraska does employ at a FEW select locations half of Philosophy 1, such as on the west side of Kearney (pronounced kar-nee), Nebraska. The counterpart arrangement is several miles to the east, behind the camera.
Does anyone know what successes the railroads are having with each preference?
Do you have a philosophy preference?
Personally, I would go with the best of both worlds, and add two more crossovers to Philosophy 2 for complete flexibility. Of course, I am not foot
You, nor I , nor anybody else’s “preference” has to do with the configuration. Each interlocking is designed for the given location within the railroad’s operation: it is what the railroad either has to do or wants to do at any given point that makes the determiniation. That same diagram may or may not work anyplace else on the railroad or on any railroad anywhere else.
Interesting questions - and an opportunity for the ‘professional railroaders’ here who have to deal with such things on a daily (if not hourly basis) such as BaltACD - to share the benefit of their training, experiences, and insights. Perhaps we can obtain a better appreciation for the ‘whys and wherefores’ / advantages and disadvantages of each configuration - and other possible ones if we ask the questions a little differently, such as this - note that there might be some duplication here:
Which configuration is preferred for a ‘universal cross-over’ location, where the goal is to be able to route a train on any track to any other track ?
How often will these moves be performed simultaneously by 2 trains on different tracks - ‘in parallel’, so to speak
Boy what a bucket of worms. On the NEC in 4 track territory I have observed crossovers start at one outer track and ladder all the way to the other outer track and then reverse and ladder back out to the original track. That really takes a lot of real estate ( maybe 1/2 mile+?? ). Signaling really has to be flexible so track occupancy or potential occupancy in the interlocking limits can be accomodated. Its been too long to remember the various signaling set ups.
Another set up to reduce track space is to switch outer tracks to 2 middle tracks and then cover the 2 tracks in the middle. Diagrams are almost endless.
Then again I have seen other track applications such as KP posted.
Generally there are operating considerations on each track that are not readily apparent when looking at the individual Control Point. Do we have a industry on Track #1 that will have a local or road switcher occupying that track for a significant amount of time. Do we have Track #3 being the entry track to a outlying yard.
From a selfish Dispatching viewpoint, Option #1 is the most satisfactory, most of the time; being able to cross from any track to any track in either direction. In the freight world, parallel track crossing over at the same time would be a very infrequent operating condition, infrequent enough as to not warrant the additional expenses. From a selfish Dispatching viewpoint…ANY control point in multiple point territory should have the ability to cross trains from any track to any other track at the control point in either direction.
The equation gets more complex when there are leads to other facilities that are a part of the control point…lead to a yard, lead to a industry etc. etc. as the relationship of the crossovers to the leads will dictate specific operating practices.
I haven’t seen diagrams, but I’m fairly certain that Park (the control point between Elmhurst and Proviso) has capabilities of moving trains from any of the three tracks west of it to any of the six main lines or leads to the east of it, as well as the ability to simultaneously line up crossover moves for two trains at once (I’ve seen that done!).
Having said that, I have to state that, despite the fact that crossovers are being built practically under my nose here in Lombard, I have no idea which alternative will be used (I’m pretty sure there will be eight switches involved, but I can’t even guarantee that). My suspicions are that trains will be able to cross from Track 1 to Track 3 and vice versa at this point, because it’s far safer and more efficient to have commuter trains using platform tracks than attempting to pick up and drop off passengers while on the center track. Besides, when everything’s done that’s supposed to be done along this line, pedestrian access to the center tracks will be removed, eliminating the possibility for the scoots to stop at certain stations (Lombard included) when they’re on the center track. Not bad if an express service is designed to utilize the new flexibility that the crossovers will give, but murder to any midday or evening service!
I would say in a general situation the number one set up would be preferred. In order to go from track one to track three in the #2 there would need to be two additional switches for each direction.
I agree that special considerations will impact on which pattern of crossovers will best serve a specific location But it seems to me that having the option of allowing two trains to use crossovers at the same time, in either direction, whether or not the two trains actually passed or ran parrallel through them, would be a dispatchers plus. Just set 'em and forget 'em. Metra north out of Chicago on the UP, north of the “puzzle dwitches” (slip switches), have highly polished parrallel crossovers.
What bothers me about two trains crossing over at the same time, either opposing or side by side, is that both sets of crossovers/turnouts are within the interlocking limits and since one of the three tracks is used by both trains, could you get a signal for the double move?
If simultaneous crossover moves are permitted by the layout of the plant, this is no problem at all–and it’s a thrilling sight for me to see a pair of Diverging Clear indications next to each other at Park from time to time.
Think you could prevail on one of our photo-capable types here to get a shot of that sometime - at least the signals, and maybe if we’re really lucky, a pair of trains making that move ? Just a wish, that’s all . . . [:-^]
I hope someone can, Carl…makes me think of a Friday night in the late 50’s or early 60’s at Bound Brook, NJ. A group of us were watching the action when one pointed to the west where the signal bridge dispayed for side by side green signals! Everything was going west that night! Another similar sight was often seen at Denville where the side by side signals at the west end of the interlocking were both green meaning that track one (westbound track, on the right) would be handling either a passenger extra or, more likely, one of the evening freights from the piers; track 2 would mean that traffic had been reversed on the normal eastbound track and that probably the electric from Morristown and Hoboken would race on to Dover ahead of the track one move or #7 The Westerner would be going up 2 to pass the freight or possilby a Boonton side was gonna scoot around the freight and lead it into Port Morris from Dover. But watching the side by side green boards with trains side by side clipping them down simultaneously was a great light show that only the railroad could give us!
I have always enjoyed the “Full Interlocking” concept the most (Philosophy 1), but like mentioned above it does not matter what people like but what is needed.
This is a neat subject. I remember wondering what was the plans at CP Cajon when K.P. had posted a construction photo of the two to three track transition with multiple switches on each track.
So if we have:
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Would this be a good combination? I am sure the guy who sells switches would like it.
But Rdamon, the excercise isn’t to build a big interlocking but rather a functional one. If one switch or crossover will do, then why use two or more? An interlocking has to address a purpose and function for the railroad based on the kind of traffic, the direction of most traffic, the speed of traffic, etc. The railroad engineers (not the train drivers) design an interlocking that will allow traffic to move in the most efficient way based on so many different factors but the switch salesman’s Christmas bonus isn’t one of them.
BT CPSO 266 - You’re quite welcome - glad you enjoyed it. It’s a different way to look at these situations, and kinda fun - I don’t ever recall seeing it addressed this broadly before. By the time it gets down to my level, the decision of “We want this configuration” or the question of “See if this arrangement can be fit in that space” has
Thanks for the in depth explanation. It is kind of ironic, because I am learning about concepts (like tangent curves) in Highway Engineering right now. Actually could give you the formula for it, [(-D].
Seriously, very much appreciated, I pretty much understood the basic concepts, but you definitely added valuable information. [bow]
