Paul,
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, .
Seriously, very much appreciated, I pretty much understood the basic concepts, but you definitely added valuable information.
30 29 OB OB 1 2
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|xxxxxxxxx| Signal bridge
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----|-|-|---
----|-|-|--- Poplar Avenue
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|/|/|
|xxxxxxx| Signal bridge
----|-|-|--- Haven St.
1 2 3
This is how Park, the control point east of the station at Elmhurst, works. As you can see, any train from any of the six tracks to the east (top of the page) can move to any of the three tracks to the west, and vice versa. The eastbound signal bridge is just to the east of Haven Street. A westbound signal bridge governs the two outside tracks only; the other four tracks each has its own pole-mounted set of signals.
At the top of the diagram, 30 Main and the 29 connector ("New 29") go to Yard 9, the two "outbound" tracks go to Global 2 and the Proviso departure tracks, and Tracks 1 and 2 go around the yard, for commuter trains and through freights. A third main line is also supposed to be built around the yard, but I don't know yet how this control point will be affected. The mainline crossovers are good for 40 miles per hour (30 for freights).
Carl
Railroader Emeritus (practiced railroading for 46 years--and in 2010 I finally got it right!)
CAACSCOCOM--I don't want to behave improperly, so I just won't behave at all. (SM)
K. P. Harrier [snip] 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.
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 usually already been made.
K.P.'s 1st photo that I've quoted above illustrates a couple of the constraints. At first, I was going to use to just refer to the 'S'-curve problem, as follows: Consider a train movement going from either outer track all the way over to the other outer track. As that train traverses the middle track, it is going to encounter an S'-curve, which is formed by the 2 turnouts in the middle track that it is using being pointed in opposite directions but being of the opposite 'hand' - they're either all Left-Hand turnouts, or all Right-Hand turnouts - trace the route and you'll see what I mean. S-curves should have a tangent of at least 100 ft. and up to as long as 500 ft. between them - mainly depending on the prevailing speed, of course - to avoid bad coupler angles and coupler-car-track interactions that could cause a derailment of some kind. So the Points of the Switches of those opposing turnouts are spaced that distance apart to prevent that problem - see the above photo. But that uses up several hundred feet of track and lengthens the whole interlocking without adding any more functionality. So, the question should be asked - "Can we do anything else useful within that distance ?" Well, the answer is yes - and again, see the above photo. What's been done is to insert one of the turnouts for the other crossover 'chain' into that otherwise 'wasted' distance as a 'trailing point' switch, which doesn't harm the first crossover at all - other than making life complicated for the signal people. As a result, the overall length of this form of crossover' is just a little over half the length of the entire 'universal' crossover as shown in K.P.'s 3rd photo of the UP at Kearney, Nebraska, x 2.
But another factor that K.P.'s 1st photo above also illustrates is the site's physical constraints on overall length of the crossover - here, it's the 2 adjoining curves - 1 is clearly at the bottom of the photo, and the other is at the top, mostly hidden behind the signal heads. A major principle of railroad track design is to avoid placing turnouts in curves or their spirals, and we can see that has been followed here. But the Points of Switches of the both the near and far 2 turnouts in the right track of the above photo are not far from the ends of the nearest curve - there's clearly no room to fit much of anything else in that short tangent distance without getting tangled up in one set of curves or the other and running afoul of that principle. So the primary reason for this arrangement may be simply that there's not enough tangent track distance here - or maybe anyplace else acceptable nearby, judging from the steep terrain in the background - for any other configuration.
Other such potential obstacles to spreading-out and installing a more flexible longer crossover configuration would be such things as piers for an overhead highway bridge between or close to existing tracks, such that the 3rd track is on the other side of the pier; a major bridge or parallel bridges that can't be easily altered to accomodate the turnouts and crossover tracks on the deck; a tunnel; a station platform between the tracks; a comparatively sharp and steep vertical curve in the tracks that can't be 'eased' out in the profile - turnouts aren't supposed to be within them, either; a major grade crossing that can;t be moved; a railroad at-grade crossing or junction turnout that likewise can't be moved easily, etc.
Then too there's that lead track coming in from the upper left that likely caused a need for the mainline tracks to have some flexibility in routing trains past it - note that if a train was occupying that lead and the left track in the bottom foreground, a train approaching on the left track from the top background could diverge to either the middle or right track without interference by the train on the lead.
- Paul North.
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.
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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:
A:
B.
Would this be a good combination? I am sure the guy who sells switches would like it.
C.
Robert
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.
I enjoyed your explanation very much Paul
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!
Carl, and others -
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 . . .
henry6 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?
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.
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.
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.
Just an outsider making an observation.
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!
Paul_D_North_Jr 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:
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:
Way above my pay grade. I just follow the lights.
But if I'm making overtime, then give me whatever creates the biggest bottleneck.
It's been fun. But it isn't much fun anymore. Signing off for now.
The opinions expressed here represent my own and not those of my employer, any other railroad, company, or person.t fun any
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.
Never too old to have a happy childhood!
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.
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 ?
Which configuration is preferred for a 'bi-directional middle track' location, where the goal is to be able to route a train running in the normal direction on either outer track to the middle track ? (only - not to the other outer track)
Which configuration is preferred for an interlocking where routing a train onto the far 'opposite' direction main line is only rarely wanted ? Is a 'trailing' cross-over an acceptable option ?
Which configuration is preferred for taking one of the tracks out of service for maintenance, etc. - where the primary goal is to be able to route a train running in the normal direction on either outer track or in either direction on the middle track, to either one of the other 2 tracks remaining in service ?
Which configuration is preferred for the most routing flexibility when there is a branch also joining at the interlocking ? See the left side of K.P.'s 1st photo above, right underneath the left-most signal heads.
It also occurs to me that maybe a 'beginner' or threshold question to be addressed first is the subsidiary one of - Which configuration of crossover is preferred in just a double-track situation ? For example, is it better to have the 'facing-point' cross-over first and then the 'trailing-point' X-over, or vice-versa ? Is that answer affected by the considerations above ?
P.S. - It occurs to me that maybe the answers for each track are at least partially driven by the configuration of the adjacent crossovers in each direction, so as to form a chain of 'passing sidings' end to end. Then again, what's the point of that ? If a train is going to leave one such 'siding' only to enter the next one on the other end of the interlocking, it might as well stay where it's at. Instead, set up the cross-overs so as to make the middle track a passing siding for the outer tracks on an alternating basis, so as to provide maximum flexibility.
Of course, this all presumes 'all other things being equal', such as no dominant grade in one direction, no unbalanced traffic flows at certain times, etc. which would favor one direction over the other. Any of that might well lead to a single preferred arrangement. - PDN.
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.
Triple-Track Crossover Philosophies (w/ Photos)
Which philosophy appeals to you?
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 footing the bill either!
----------------------------------------------------------------------------------------------------------------------------------- K.P.’s absolute “theorem” from early, early childhood that he has seen over and over and over again: Those that CAUSE a problem in the first place will act the most violently if questioned or exposed.
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