Tonnage pulling

Rough estimate   1 horse power per ton.  A  3000  horse powered engine can pull about 3000  tons  on a grade with   moderate grades.

@ rrman  It has been quite awhile, but from what I can remember, the formula for calculating the tonnage pulled depended on the number of tons each powered axle on a locomotive was capable of pulling. On the NYS&W, CSX ran test trains and determined no more than twenty four axles on- line at one time was optimum power for pulling a loaded stack train without breaking a coupler. I can't remember exactly how many platforms the train had or the tonnage. I do remember it was at least a mile long. 

Thanks Greg and Paul.  I thought that maybe there was a rule of thumb or a multiplier to get a ballpark figure, so as to not over/under do it.

When NYS&W ran the worn out Alcos and SD45s on stack trains and extra unit always came in handy. I can remember getting a shove up to Smoke Rise from Butler by the local job on more than one occasion.

Yeah, all of the above. You forgot ambient temperature, localized rail conditions, curvature, tunnels, sand, ruling grade %, length of ruling grade, speed entering ruling grade, and a few other I forget......

Perhaps the most important is any drawbar pull anywhere in the train that exceeds about 360,000 lb. of buff force, as the knuckle goes.........sometimes several.....

and that is why some railroads use mid train slaves, some use pushers, etc.

Wyhog,

I believe that the present MCB couplers will accept a continuous force of about 360,000 lb. Any buff force, positive or negative, above that number then would risk a coupler knuckle. I understand that buff normally occurs in DB, but buff can also be localized anywhere in the train when either in traction or braking, and is most common on profiles where some of the train is "going uphill" and other cars are "going downhill". Buff forces above the level of the yield of a coupler knuckle pin or knuckle would most likely occur with helpers. The earliest computer based train application programs treated the train as a "point", and of course there were "undesirable" consequences as a result.

So you are correct with your post.

RR's generally set tonnage rating of locomotives at their minimum continuious speed. This was about 12MPH with 1st generation power geared for 65MPH (most road freight units)  At this speed a locomotive is capable of maximum horsepower --AND-- adhesion.  Take the weight of the unit & figure an adhesion rate of .15 (Bad Slippery Rail) to .24 (Excellent dry sanded rail) and that is the Tractive Effort the locomotive is capable of achieving. Note: these adhesion figures apply to DC traction motors only, AC motors are capable of higher adhesion levels because they are synchronous between their individual pairs and thus not so prone to slip as individual DC traction motors.

Knuckle strengths give above of 350/360K are accurate.  40 years ago we had standards on Southern Railway of no more than 18 traction motors at any one location in a train (20 traction motors with F-Units) to limit distructive draft forces in the head 1/3 of heavy trains.  Even with these limits in force, at minimum continuious speed it was absoutely necessary, to keep a train together, when cresting sever ruling grades to reduce the throttle one and sometimes two notches.  This had the effect of reducing the tractive effort as gravity caused the head of the train to accelerate without excceding draft drawbar forces that were already at peak levels. The skill was to balance increased gravity with reduced tractive effort...if done correctly the speedometer would not gain a single MPH as the head 1/3 of the train crested the grade.  This technique was the difference between getting 10 out of 10 trains over a mountain instead of 7 out of 10 and tying up a mainline while the other three crews cleaned up their scrap iron. 

The subject of train handling in mountainous territory could fill a book. These guys have my respect. I have read trip reports that referenced "cycle braking" on undulating profiles and the method used to find out what worked...a lot of trial and error. I remember one trip report, on a RR now gone, in hauling coal over a rolling profile and the brake cycling used. When the author of that report ask..."how in the h*** did you figure that out?" The Road Foreman said that they broke up a lot of trains, and the record was a train that broke into seven sections. He also added that "the one broken into seven sections also threw the caboose stove through the back door of the caboose and onto the roadbed....."

Further my previous post: when considering what a locomotive will pull (tonnage rating) you must consider adhesion (how much weight of the locomotive can be transferred into pulling power) and horsepower.  Horsepower is a measure of how fast work can be done: thus a constant 3000HP SD-40 is capable of doing a lot of work at slow speed or a little work at high speed.  Adhesion is greatest at starting and slow speeds and then tapers to a constant value somewhere around 25MPH. The adhesion curve & the horsepower curve intersect at about 12/13MPH (an over simplification of fact) and it is at this point the locomotive can produce its maximum effort.

Using HP/ton is a measure of how fast an engine can pull a given load.  This measure is used by some western roads in assigning horsepower to trains because they want to make a speed better than minimimum continuious speed on grades.  This means the locomotive is not pulling its maximum tonnage rating and is considered wasteful horsepower by some eastern (read heavy coal)properties who set tonnage at the minimimum continuious speed.

HP/T or Tonnage Rating for locomotive is calculated for ruling grade ( single steepest grade on division) not entire division.

The US Dept of Transportation cites 22.5 mph for average freight train speed in 1997. Wasn't the average in WW I something like 16 mph?  Recall a guest editorial in Trains many years ago, where the author mused "Why run the wheels off a train, just to sit in a siding for several hours?"      Guess that's the dilema for our railroads - insufficient physical plant to achieve maximum efficiency. Wyhog's solution is the less then perfect solution: plenty of horsepower to get trains to sidings as quickly as possible!

There's   old rail road joke.. I spent 40 years with the railroad, 30  on the mainline and 10 sitting in the siding waiting for other trains. 

An application study that is done with the assistance of RR operating people can answer some of these questions but not all, and here is where operating experience counts. For example, by cycling the power in an optimum fashion, the capital expenditure for a quantity of new locos can be reduced, with fewer units ordered. How many crews are used and how many "outlaw"  has to be considered. The physical plant, including reverse signaling on multi track, location of siding and crossovers, etc. has to be included. The average speed of freight trains has not significantly improved in probably 60 years. In the old days, it was the HP assigned to the train. (Dieselization slowed down this "system" because diesels could haul a lot more tonnage than steam could, but they usually ran slower with these much greater train lengths. The lengths were sometimes limited by length of sidings and not the power.) The slowest train slows down everyone else. Today, it is congestion.

 The lengths were sometimes limited by length of sidings and not the power.) The slowest train slows down everyone else. Today, it is congestion.

This one made me smile a little.  The railroad I worked for would run about 4 express trains on the block of one another after midnight each day heading  west out of Toronto. All of them were over siding capacity . If  you were east bound on a heavy drag you usually ended up in a siding for the works.   Every now and then someone would slip up and  a east bound would end up being  over siding capacity as well.  Zig -Zaging with a full crew back then was bad enough. I can't imagine what the crews do now.   Anyway talk about delay.