In looking at employee timetables, for a given section of the railroad, I've found where the timetable will show sections as single track, sections as double track (DT) and other sections as two main tracks (2MT). What would the difference be between double track and 2 main tracks?
I'm guessing that one might be restricted to directional / current of traffic running vs. the other may be signalled in both directions, but that's just taking a guess.
Any help would be appreciated.Thx,
Stack
You guessed right...double track means two tracks that see traffic in both directions,although some do have a "normal direction" of traffic movement depending on that railroads operating rules...two main tracks are often, but not always, run on a directional basis...main one for westward movement, main two for eastward movement.(or north and south, depends on the railroads preference and terminology)
Mainline tracks under CTC and ABS have their own set of paticular rules in the GCOR.
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Double track implies that they are operated using a "current of traffic" method. The rule varies by rule book, but its sometimes referred to as rule 251 territory (or rule 9.14 if you use the modern GCOR). Trains operate in the same direction on one track and the other direction on the other track. It may only be signaled in one direction on each track.
Two main tracks are operated in either direction on either track. They are signalled in either direction on either track.
Typically double track is operated with ABS signalling and train orders (or track warrants) and two main tracks is operated with CTC signalling.
Dave H.
Dave H. Painted side goes up. My website : wnbranch.com
Both mains and double track have crossovers, and specific rules as to how, when and who can use them.
One of the "rules" about main line crossovers requires the crossover to be restored or lined for the normal movement of traffic at all times, except when in use for the crossover, and requires the crew, if the switches are not controled by the dispatcher, to verbally confirm the switches are restored for normal traffic.
The same rule applies to sideings, you have to line back, and verbally inform the dispatcher or control operator that you have done so.
Shepard Texas, and the SC chlorine disaster are prime examples of what happens when this rule is not followed.
One of the additions to the rule now requires the locks on main lines switches to not lock unless the key is inserted, nor will they release the key untill the lock is closed.
You cant forget to lock the lock, unless your willing to forget your keys too.
What's confusing you?
D.E. Husman's post is accurate.
1435mm wrote:What's confusing you?D.E. Husman's post is accurate.
Maybe it is just me, but Ed's (first) post and Husman's post seem to be contradictory. I notice that you were thoughtful enough to clarify that it is Husman's post that is accurate. Thank you.
Murphy Siding wrote: Is it possible, that double track has crossovers, to allow for bi-directional running? Double track would be two, parallel tracks, where a train can't be switched from one track to the other?
Double track can indeed have crossovers but they are hand-throw and if a train uses the crossover it is now running against the current of traffic on the wrong track, and thus has no signal protection.
If you see crossovers in double-track that are signaled, they are not crossovers in double-track at all, but is CTC or an interlocking and it is multiple main track.
People do get confused by this stuff. It usually stems from people using definitions that are imprecise while the railroad industry uses definitions that are highly specific and limited, e.g., they see two parallel main tracks and think "aha, that must be double track." Well, it could be Double Track and it could be Two Main Tracks. To know which it is you need to either look at the employee timetable and see what it tells you; or, if you know something about signaling and Methods of Operation, you can study it and figure out which it is.
Rules of thumb:
1. Look at the intermediate signals (the ones with number plates). If the track is signaled in both directions with numberplated signals, it's two main tracks.
2. If the intermediate signals are one direction only on each track, it's double-track.
3. If there is two tracks that both appear to be mains, and neither is signaled, it could be dark double track. This is quite rare, however.
Double-track often begins and ends in control points that are, within their limits, short sections of multiple main tracks. Control points have to be signaled at all entrances, thus there will be a signal facing the "wrong way" on one of the double tracks. You can tell a controlled signal because it has no number plate.
S. Hadid
Datafever wrote: 1435mm wrote:What's confusing you?D.E. Husman's post is accurate. Maybe it is just me, but Ed's (first) post and Husman's post seem to be contradictory. I notice that you were thoughtful enough to clarify that it is Husman's post that is accurate. Thank you.
I'm copying Ed's post because I can't think through too many things at once:
"You guessed right...double track means two tracks that see traffic in both directions,although some do have a "normal direction" of traffic movement depending on that railroads operating rules...two main tracks are often, but not always, run on a directional basis...main one for westward movement, main two for eastward movement.(or north and south, depends on the railroads preference and terminology)
Mainline tracks under CTC and ABS have their own set of paticular rules in the GCOR."
I think the first sentence is indeed unclear, in part. Double Track is a Method of Operation (a term of art) that is "current of traffic," either right-hand or left-hand, always, unless trains are running against current of traffic (which is an unusual condition). Two Main Tracks is a different Method of Operation where either track is regularly used in either direction. It is true, as Ed points out, that one track tends to be mostly eastward/northward and the other mostly westward/southward, but that is more due to the limitations of crossovers (too far apart and/or too slow) and train density patterns than because the railroad "has" to operate that way. On a well-engineered 2MT plant with a good dispatcher, you'll see lots of weaving of fast trains around slow using the crossovers. A poor dispatcher will run it as if it was double track and make no use of the plant's flexibility.
For what it's worth, most of us typically use "double track" in meetings and discussions to discuss construction of 2MT, because it rolls off the tongue faster, even though we all know it's technically and correctly 2MT. In formal documents we try to use the correct nomenclature, and in the employee timetable, it will assuredly appear the correct way!
Brian (IA) http://blhanel.rrpicturearchives.net.
Thanks very much for the replies and information folks. I appreciate it much,
- - Stack
To expand slightly - Back when ICG had two sets of tracks through central Illinois, it was apparently "double track." I saw several instances where the station agent at Rantoul would hand up orders to a northbound which would then use the crossovers just north of the station to switch to the southbound track. When I asked the agent about it, he said that there was trackwork on the northbound track so they had to issue orders so the northbounds could use the southbound track.
I don't recall that the track was signalled in both directions.
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tree68 wrote: To expand slightly - Back when ICG had two sets of tracks through central Illinois, it was apparently "double track." I saw several instances where the station agent at Rantoul would hand up orders to a northbound which would then use the crossovers just north of the station to switch to the southbound track. When I asked the agent about it, he said that there was trackwork on the northbound track so they had to issue orders so the northbounds could use the southbound track.I don't recall that the track was signalled in both directions.
It probably was not - just in the direction of the current of traffic.
The SP had several Double Track situations, the busiest was between Sacramento and the Bay Area. Right had running. Signaled for right had running only. Should movements be necessary against the current of traffic, a whole gob of orders needed to be put out to everybody and entrance into that section of track that was being operated against the current was required to be flagged (Rule 99) an each entrance or corssover (if not at an interlocking or an open TO) and Rule 251 applied, or controlled switches and signals lined and locked for the move. Trains operating against the current of traffic almost always were restricted to Restricted Speed because they had no signal protection.
blhanel wrote:Would UP's on-going improvements to the Iowa transcon be correctly described as converting it from double-track to two main tracks?
Yes. When ever a new portion of CTC is cut in, the general order revising the time table changes the Rule 6.3 column from DT - ATC to CTC 2MT - ATC.
Now if you read thru the special instructions for a particular subdivision, the Clinton Subdivn for example, there is a listing in part SI-04 MAIN TRACK DESIGNATIONS. It has Two Main Tracks: MP 2.1 to MP 202.2. That's the entire subdivision including parts under DT and 2MT in the 6.3 column. Confused yet?
The Rule 6.3 column is for Main Track Authority. It tells what method of operation is used on the track(s), how a train or engine can be authorized to use the main track(s). The SI-04 tells you how many multiple main tracks there are and between what locations they are considered main tracks, but doesn't give what authority is used. The reason you need to know is that there are rules that apply to operating on main tracks and some that apply to other than main tracks. You could have a stretch of multiple tracks that look to all intents to be main tracks, but technically are one single main and one auxiliary track.
Jeff
kenneo wrote: tree68 wrote: To expand slightly - Back when ICG had two sets of tracks through central Illinois, it was apparently "double track." I saw several instances where the station agent at Rantoul would hand up orders to a northbound which would then use the crossovers just north of the station to switch to the southbound track. When I asked the agent about it, he said that there was trackwork on the northbound track so they had to issue orders so the northbounds could use the southbound track.I don't recall that the track was signalled in both directions.It probably was not - just in the direction of the current of traffic. The SP had several Double Track situations, the busiest was between Sacramento and the Bay Area. Right had running. Signaled for right had running only. Should movements be necessary against the current of traffic, a whole gob of orders needed to be put out to everybody and entrance into that section of track that was being operated against the current was required to be flagged (Rule 99) an each entrance or corssover (if not at an interlocking or an open TO) and Rule 251 applied, or controlled switches and signals lined and locked for the move. Trains operating against the current of traffic almost always were restricted to Restricted Speed because they had no signal protection.
Freight trains operating against the current of traffic can run up to 49 MPH.
Here's an example of a Rock Island (Uniform Code) Form D-R train order. It was issued on The RI's east/west main line in eastern Iowa. Specifically that part of Subdivision 4 between Missouri Division Jct and West Liberty that was two main track Rules 450 - 453 territory.
TRAIN ORDER No. 210 Oct 26 1979
To C&E EXTRA 4515 WEST
At DURANT
EXTRA 4515 WEST HAS RIGHT OVER OPPOSING TRAINS ON EASTWARD TRACK
FROM CROSSOVER MP 201 POLE 25 TO CROSSOVER MP 208 POLE 3
DAL
Made Complete 953AM (signature of ) Goodwin Operator
Eastward trains would have received this order at West Liberty, Iowa. Eastward trains would have to stop short of the crossover at MP208 Pole 3, near Wilton, Iowa and wait for Extra 4515 West to clear unless they had already met it operating back with the current of traffic west of 208+3.
Doublestack wrote:In looking at employee timetables, for a given section of the railroad, I've found where the timetable will show sections as single track, sections as double track (DT) and other sections as two main tracks (2MT). What would the difference be between double track and 2 main tracks? I'm guessing that one might be restricted to directional / current of traffic running vs. the other may be signalled in both directions, but that's just taking a guess. Any help would be appreciated.Thx,Stack
A more important set of differences are capacity and cost.
Capacity: 2MT CTC is typically good for 70-75 trains per day average capacity, whereas double track is typically good for 45-50 trains per day average capacity. The difference lies principally in track maintenance restrictions. When engineering has track & time with 2MT CTC the railroad only loses to revenue service the section of main track between the nearest control points, which is typically 10 miles or less in U.S. practice, and trains running on the single track that remains in service can continue to run on signal indication at maximum authorized track speed, with following moves also proceeding on signal indication at maximum authorized track speed.
With double track the distance between control points is usually much longer -- often as much as 100 miles -- and while there might be hand-throw crossovers or center sidings with a spring switch at one end subdividing that distance into 10-20 mile segments, the crossovers and center sidings are typically hand-throw, if signaled typically nothing more favorable than a lunar, and thus restricted to 20 mph or less. One-half of the trains will be running against the current-of-traffic and cannot proceed on signal indication and require a verbal authority, and following moves against the current-of-traffic are greatly limited in frequency because they have no signal protection against preceeding moves (no flag protection). Trains running against the current of traffic are restricted to 49 mph (freight). (Theoretically when single-tracking occurred the railroad could run as manual block and the 49-mph limit would no longer apply, but that introduces some new limitations on capacity. I don't know of anyone that has ever tried this.)
The 70 trains per day average for 2MT CTC is based on 60% of theoretical capacity. Some people in network planning and traffic modeling, particularly some of the people selling their expertise in those areas, tout a capacity of 75% of theoretical is attainable, presumably if you adopt their operating methods. In our long experience 60% has proven the sustainable upper limit. Above that level the network becomes fragile. While one might briefly sustain a higher number, inevitably weather, mechanical, or other outside factors soon intrude. Because the network has little freedom to adapt to the unforseen, congestion if not gridlock rapidly ripples outward from the point of injury and trains can no longer be accepted at the network entrances ... and capacity goes to 0%.
Cost. No one has installed very much double-track ABS in about 50 years, but if one was to do so today the expenditure for signaling and control points might be about 50% as much as would be spent for 2MT CTC, assuming that 2MT CTC would include a universal or split crossover with four #20 or #24 movable-point frog turnouts every 10 miles, and double-track ABS would include two #14 or #15 handthrow crossovers every 20 miles, and control points every 100 miles or so (at the crew changes). In rough terms the difference is about $1 million per mile. That of course is on top of the $1 million per mile for each track exclusive of turnouts, bridges, drainage structures, earthwork, subballast, grade crossing warning devices, grade separations, ABS, etc.
kenneo wrote:Trains operating against the current of traffic almost always were restricted to Restricted Speed because they had no signal protection.
Hopefully that's not true now, is it? In the past Amtrak on the SP was allowed the usual 59 mph on such "unsignalled" track.
Hell I'm kinda embarassed to admit it, but I didn't even realize that there was a difference (pretty scary).
I guess that's because we only have one section of railroad in my territory that's double main (now that I know the difference). We (including the TTD) have always called it the "double track", though at times we call it "double parking". It runs between Dallas and Ft. Worth.
timz wrote: kenneo wrote:Trains operating against the current of traffic almost always were restricted to Restricted Speed because they had no signal protection.Hopefully that's not true now, is it? In the past Amtrak on the SP was allowed the usual 59 mph on such "unsignalled" track.
Those were the days when the SP had their own rule book. Pre FRA. I think the line is now CTC 2MT. The restriction had to do with a couple of nasty head-ons and San Francisco wanted the trains to be able to stop prior to any smash.
SP had their own rule book and did not change over to the Uniform Code until the late 1980's when the FRA forced them to. Changed all sorts of things we had done.
For instance, prior to the UC, if you wanted to run against the current of traffic and the track was signaled only one direction with the current, you had to obtain the Chief Train Dispatchers authority.
Our TO signals were always at stop to prevent trains from getting past you. The trick dispatcher had to authorize any other indication. Changed with the FRA and the UC.
Are you saying 59 mph against the current is no longer allowed anywhere in the US?
(By the way, SP's 1996 timetable shows 59 against the current on the Cal-P.)
"prior to the UC, if you wanted to run against the current of traffic [on the SP] and the track was signaled only one direction with the current, you had to obtain the Chief Train Dispatchers authority."
In what form?
Data,
Mr Hadid and Mr Hausman have the more definitve answers...
Run out the Hardy toll road if you ever get down here...UP's Palestine sub...beautiful, and almost brand new double main all the way to Old Spring...and they have almost no choice but to run it on a directional basis.
During the SP/UP "meltdown" they discovered the hard way that when you park inbound trains on both side of a double main, it causes more problems that you can imagine!
One dispatcher error, and one train parked in the wrong block destroyed the ability to zig zag around the parked trains...so now, almost all inbounds arrive on one track, and outbounds leave on the other.
But for the most part, it works the way Mr Hausman and Mr Hadid say.
One of the best uses of double mains is to allow one train to over take another, hence the signaling and power crossovers, this allows the dispatcher to run say, a hot intermodal around a train that has died on the hours of service, or a lower priority train that is in the way.
Datafever wrote: 1435mm wrote: What's confusing you?D.E. Husman's post is accurate. Maybe it is just me, but Ed's (first) post and Husman's post seem to be contradictory. I notice that you were thoughtful enough to clarify that it is Husman's post that is accurate. Thank you.
1435mm wrote: What's confusing you?D.E. Husman's post is accurate.
Thank you for the clarification, Ed.
Another question (I hope that this wasn't answered already and my eyes just glossed over it) - do both DT and 2MT have sidings in the same way that a single main line would have?
Datafever wrote:Thank you for the clarification, Ed. Another question (I hope that this wasn't answered already and my eyes just glossed over it) - do both DT and 2MT have sidings in the same way that a single main line would have?
It wasn't asked or answered already, so you didn't miss it.
On a 1MT line the primary purpose of a sidings is to meet opposing trains. Siding spacing and length absolutely, positively, determines the capacity of the single track line. The running time between sidings that will fit the trains you are trying to meet is the ultimate limit on the capacity of the line, period.
You can use a siding in 1MT territory for overtakes, but only if there's a lot of spare capacity.
On a double-track or 2MT line, train meets are handled by the other track. Because double-track lines had very limited ability to use the other track for wrong-way moves, sidings were necessary if one was to have any overtakes outside of terminals, at least without really making a mess out of traffic on the opposing track. Back in the era when these double-track lines were engineered there were a lot of passenger trains on these lines, and the sidings were critically important so that freights could run against the schedule of a 1st Class train and not delay it or themselves.
2MT territory has complete flexibility of which track is used for which direction, so the imperative for sidings needed in double-track territory can be greatly diminished, at least if traffic is not so high that running a train "wrong main" to do an overtake can be done without inflicting serious damage on the schedule adherence of trains coming the other way. If, for example, the crossovers are 10 miles apart, the overtaking train is going to use up the other main track for at least 20 minutes during which any opposing traffic that wants to enter that 10 mile stretch is going to stop, while following trains bunch up behind it. The overtake if not done right can easily be a net loss, because it bunches fast trains behind slow on the other main, which creates needs for more overtakes, which in turn creates more need for overtakes on the track you were trying to unbunch in the first place!
Sidings in 2MT territory are also used for, block swaps, storage, terminal hold-outs, and the like, and are useful when one track is given away to maintenance-of-way because trains can meet there. (Same applied to double-track, too). If it's a controlled siding, all the better.
Some ABS double-track roads seemed to prefer outside sidings, in the West notably the Santa Fe, and some seemed to prefer center sidings, in the West notably the UP Overland Route. Generally the leaving switch (remember this is current of traffic, directional running) was a spring switch.
Single-track CTC railroads that are converted to 2MT, such as large portions of the BNSF Transcon and UP Sunset Route during the last few years, retain some of the old sidings -- if they're on the opposite side of the existing main track from where the new main track goes; otherwise they're usually retired. They're nice-to-haves from an operating department perspective, and provide another place to get the track inspector or track machines out of the way so trains can run.
But you don't absolutely have to have sidings in double-track or 2MT territory. If you think about it, one of the main tracks between crossovers in 2MT territory is in effect a "siding."
There's a lot of discussion in the business about the value, use, location, and need for sidings in 2MT territory. And if they're to be retained, there's discussion about how the turnouts should be arranged. BNSF has built some lately with nested turnouts, which in effect gives one three main tracks for the length of the siding. But that's expensive and there's debate over whether the flexibility gained is worth the money spent. Building a 10,000' outside siding in 2MT territory, from scratch, is a $2-3 million proposition. And it's difficult to demonstrate in advance how that expense will repay itself. One philosophy is that if you really need that much capacity, you might as well build a third main track. It's not an easy thing to figure out.
Thanks for the response, Ed. You mention both outside and inside sidings. Do the inside sidings normally connect to both of the main lines?
I could see that one of the main uses of sidings with DT/2MT would be for overtakes, particularly if they frequently need to happen in the same general location.
By general (if not book) definition a center siding is connected to both main lines, i.e., if you say "center siding" to someone, they would recognize you're talking about a siding that lies between the two main lines connected to both, usually with an equilateral turnout on the siding itself leading to hand-throw main line turnouts, and spring switches on the two leaving turnouts off the main tracks. There are some instances where there is a siding between the double track that is connected to only one of them, but almost invariably this occurs in a location where the two main tracks are widely separated for reasons of local topography.
Note that a center siding has a dual function; it's also the crossover between the main tracks.
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