Difference between "Double Track" and "Two Main Tracks"

[spokyone]

How are the 3 tracks used/signalled coming from Powder River Basin?

[MP173]

Official statement....I am not a dispatcher, nor a railroader, so my opinions are subject to review and correction, because there is a great possibility of incorrectness.

However, I listen in on my local railroad operations and often on the Fostoria, Oh web feed.  There is an example of center sidings at Fostoria on the ex C&O north/side mainline which is 2MT thru Fostoria.  Center sidings are both north and south of the B&O mainline and are used for flexibility in movement of trains to and from the C&O/B&O routes.  I would recommend Trains, October 2001 as a primer if listening in on Fostoria, as it contains an excellent overview plus a map.  Interesting how the local tower operator uses his sidings, crossovers, and wyes to keep the traffic flowing.

I am really interested in knowing how a company will determine if capacity increases either thru more MT or advanced signalling will be approved in a capex model.  No doubt there must be an internal rate of return which must be surpassed, but what types of models are used to determine if these projects are completed?

ed

[Anonymous]

How are the 3 tracks used/signalled coming from Powder River Basin?

All of the main tracks on the coal line are CTC, and by definition a train can move on signal indication in either direction on any of the tracks.  In practice it works out that way too.

S. Hadid

[Anonymous]

I am really interested in knowing how a company will determine if capacity increases either thru more MT or advanced signalling will be approved in a capex model.  No doubt there must be an internal rate of return which must be surpassed, but what types of models are used to determine if these projects are completed?

ed

You're asking about what I do for a living, most days. 

There are several consultants that provide traffic modeling and capacity studies for the railroad industry.  The process is iterative as one first hypothesizes a given traffic level, train type, hp/ton ratios, priorities, and a given fixed plant layout that includes proposed locations of crossovers, turnout sizes, siding lengths, signal aspect progressions, and other features that affect capacity such as location and type of grade crossings, curvature, and gradients.  Thought is also given to maintenance provisions and the effects of traffic and terrain on maintenance, such as curve rail wear, rail corrugation on ascending grades, accessibility of the main track to maintainers, etc. Then a computer simulation is run and the results studied. 

Because freight traffic is irregular and there are events that are unpredictable such as weather, grade-crossing collisions, mechanical failures, etc., the model only shows you the results of each scenario that is posited.  In the real world of railroading no two days are alike.  And the locations of track features you might want to add, such as crossovers and sidings, are highly cost-dependent upon terrain features.  So there is very much less flexibility and choice than you would like.

The end result requires experience and judgement to look at the proposed track arrangement and method of operation, and conclude that it will reasonably support the proposed traffic.  The computer model is not a substitute for experience and professional judgement.  In fact, you had better have a very good understanding of what you're doing even to set up the information you feed into the computer model, or the results are garbage. 

At the end, the cost of building the capital improvements are compared to the projected revenue stream and the project is ranked on the railroad's capital projects list.  But if you're looking for a computer model that will tell you that a new $1.2m 40-mph crossover at Smallsville is more attractive than a $2.2m 10,000' siding at Bigtown, you will look in vain.  Fortunately there's a huge experience base -- about 175 years worth -- of what works and what doesn't, and most of the time we get it reasonably right.  Railroading is an old game and most of the truth was figured out and very closely understood by the 1890s.  And one of the truths is that network operations are extremely complex, extremely vulnerable to small things having big effects, and that it is not reducible to simple nostrums or computer models.

S. Hadid 

[nbrodar]

I've never seen the term DT (Double Track) or 2MT (2 Main Track) in my timetables.  My current (NORAC) TTs list the the tracks as Rule 251 (signaled in one direction) or Rule 261 (signaled in both directions), with track numbers, ie 1 Main, 2 Main.

So, after 8 years as a professional railroad, I was unaware of the difference between DT and 2MT.

Nick

[Anonymous]

I've never seen the term DT (Double Track) or 2MT (2 Main Track) in my timetables.  My current (NORAC) TTs list the the tracks as Rule 251 (signaled in one direction) or Rule 261 (signaled in both directions), with track numbers, ie 1 Main, 2 Main.

So, after 8 years as a professional railroad, I was unaware of the difference between DT and 2MT.

Nick

2MT and double-track are the terms used in GCOR.  GCOR railroads formerly used Rules 251 and 261 for the same thing, as NORAC does still.  The original question asked the difference between 2MT and double-track, it did not ask the difference between Rule 251 and Rule 261, so none of us that answered saw any need to add that.

After my 25 years in the railroad business, I still use "251 territory" in everyday conversation, and many of the people I work with do so also.

S. Hadid 

[MP173]

Mr. Hadid:

Now that sounds like an interesting job!

Now you have really whet my appetite.  Lets say one of the large carriers has a list of capex projects and a budget....nothing different than any other business, or personal situation.  Surely there will be a number of projects with costs associated with those projects.  Somewhere there will be a estimated ROI for each project, based on best financial info available.

Typically, how is the decision made on which projects are completed?  You have outlined the computer simulation which is developed, plus the necessary "personal experience" which is even more important.  Does each division superintendent then "sell" his needs, in other words does this get extremely political, or does the VP Operations and CFO basically go thru and rank these projects? 

Much was made about Rob Krebs decisions to expand the physcial plant and the lack of business that came....until he had retired.  How does one project growth into the equation?  Do most carriers have economists on staff?  Was the explosion of import containers adequately forecast and planned for (doesnt seem so).  How is the infrastructure requirements of the railroads tied into other system's requirements such as the port's abilities?

Here in Chicago/NW Indiana we are looking at big projects which are no the planning boards including the CREATE project, plus both NS and CSX are looking at big intermodal yards in NW Indiana. 

The entire planning and implementation of these projects is fascinating and seems to signal an upcoming era of financial strength for the industry.

Times, they are a changin, or so it seems.

ed

[CNW 6000]

1435mm

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.  (snip-bold emphasis mine)

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%.

(snip)

Interesting notes on capacity.  What would the capacity of single track CTC w/'average' siding spacing be?  What of single track with operation methods other than CTC?

[Railway Man]

"An average siding spacing" is not a term that has any sort of firm meaning, but in a very broad sense, you could use the following for this scenario, based on my network operations and planning experience, and the experience of those I work for:

• North American railroad, freight only (or at most a single pair of Amtrak intercity trains daily
• Maximum Amtrak speed 79 mph
• Average freight train speed range, 40-50 mph
• No trains with hp/ton ratios below 0.8
• No grades in excess of 0.8%
• All sidings as long as the typical long train plus 400'
• Very few sidings with grade crossings that cannot be blocked for long periods of time
• Average siding spacing of 10 miles; no gaps of more than 16 miles
• No significant switching directly from the main track or a controlled siding
• No permanent speed restrictions between endpoints worse than 40 mph
• Only two Form As (temporary speed restrictions) at any one time, and none longer than 0.5 mile in length
• No Form Bs that can't be operated through at maximum authorized track speed
• Warm weather operation, no heat restrictions, no work windows
• No persistent maintenance issues anywhere
• No terminals en route
• Ability of the terminals at either end to suck up whatever the main line throws at them
• No traffic peaking issues
• No anything else

Given all those caveats, you could use as a rule of thumb:

1. Single track, TWC or DTC, with or without ABS: 15-35 trains per day (upper end of range assumes a spring switch at one end of every siding, or DTMF switch machines)
2. Single track, CTC: 25-50 trains per day (assumes all sidings are controlled sidings)
3. Double track, ABS: 60-100 trains per day (assumes no overtake events outside of terminals)
4. Double track, CTC: 90-130 trains per day (assumes no overtake events outside of terminals)

These ranges are BEST CASE ranges.  Add a maintenance window to an ABS double-track railroad of 8 hours duration, and daily capacity might instantly drop to 30 trains.  Put several persistent 10-mph, 5 mile-long speed restriction into a single-track TWC railroad and daily capacity might be 10 trains.  Railroads have to be maintained, and weather happens, so these numbers are not something you can expect to realize every day.

Note that ABS may not add effective capacity under TWC or DTC rules on single track, in fact, in some cases it subtracts capacity today, because older ABS systems can be so unreliable or track conditions so poor that it seems that every signal is a red signal and trains operate for block after block after block at restricted speed.  Under timetable and train-order rules, that was different, and in double-track "251" territory, ABS is a capacity increaser.

I am sure someone can come up with examples of lines that at one time or another have exceeded or fallen below this range.  I can think of some single track CTC line segments that have semi-regularly handled 70 trains per day, and some single-track TWC/DTC lines that cannot on a good day handle 10 trains.  So these should be treated as reasonable averages, not the exceptions of which forum posters are exquisitely fond.

RWM