After watching many rail cams, I have wondered about this: How do railroads determine how many engines to a specific train? I know that there is a ratio of horsepower to weight in tons that the trains consist weights. But how does the grade of the route play into this? If the train route has a section of 2% grade is there a formula to tell railroads how much more horsepower is needed? Is this something that data concerning the number and weight of cars needed to be moved and the specific route is entered into a computer program and then the computer responds with the required horsepower? Then are engines assigned by horsepower rating? Does weather affect the amount of horsepower needed? This leads to the following question - How is the placement of DPUs determined? This is something that railroads do and get right daily and it would be interesting to learn more about how they do it.
DPUs are usually added in yard if to little power is added in the head end of if it may be needed in the rear end I think
Welcome to the forum, RobMat!
Your question is interesting. We have some forum members who are also engineers, so I hope they will answer!
For larger railroads (particularly the Class i’s), they will have charts or tables or spreadsheet formulas that help them make sure they have sufficient power to get over the road. Most districts have a “ruling grade”, which is the usually the most difficult location for a train to get through, and tables/ charts will be built around that particular location. There can be modifiers that might cause extra power to be added in certain circumstances (i.e. inclement weather).
On smaller operations and short lines, it is more likely based on the institutional knowledge (experience) of the operating folks making their best guess on what is needed. I run tourist trains on a segment of a short line and the train that can make it up the hill with one locomotive in some conditions might need two or three on the right conditions (wet weather in the middle of leaf drop season). Also, on short lines, doubling a hill is not uncommon practice when insufficient power is available. I’m sure the Class 1’s try to avoid doubling hills at all costs on account of the disruption to traffic those cause.
Also, in some places, it is not just the power to climb the hill that is considered - the availability and positioning of dynamic brakes can factor in as well. This can include limitations on the number of dynamic brakes cut in, as too much dynamic braking concentrated in a single consist can put excess stress on the rail structure.
Normally, I go in and my engine numbers are written on our paperwork. I sometimes get a little say or a choice, or if there’s plenty of power available and they want me to do heavy switching with just a pair of GPs, I will ask for something with more wheels.
I have a rule - NEVER refuse more power. Better to have it than not need it… blah blah blah.
Welcome on board, RobMat.
David
The critical element in powering a train is ‘Trailing Tonnage’. Trailing tonnage must be held under the value that exceeds the breaking point of coupler knuckles.
All carriers have tonnage charts for the various kinds of locomotives they possess for operation on the various territories the carrier operates. Needless to say, ‘flat land’ territories allow a engine to haul more tonnage than that same engine can haul on territories with grades. Motive power performs two functions in moving trains, power to climb grades and dynamic braking to control trains descending grades.
Class 1 carriers will establish power plans for the scheduled trains of their merchandise networks, that take into consideration the normal traffic on those scheduled trains as well as the ruling grade between the scheduled end points of the train.
Bulk commodity trains (coal, grain, oil, ore, coke etc.) normally have defined train sizes and will get assigned power based on those sizes as well as the ruling grade between origin and destination.
The following is a 20+ year old tonnage chart for the territory I worked - the days before DPU.
The chart can be expanded to be readable - abbreviations are the company’s designations for end points.
SD40s on Coal Trains??? Even GP40-2s??
I believe that BaltACD’s chart shows what each unit should be able to move over the territory at a speed that would not overheat the traction motors, around 12mph for non AC units. I know from experience that it takes about five horsepower per ton to move a train up Sandpatch at the maximum authorized speed for the track. Rarely is that much power assigned since it would have a train grossly overpowered for most of its trip.
Mark Vinski
That was the newest power available at one time. It worked fine.
I do not know how they place the DPUs but I suspect part of the reason they are used it to reduce the stress on couplers on extremely long trains. Also I have never figured out why with very long trains and just head end power they do not pull the cars off the tracks on long curves.
They do - when you have long, light cars near the head end of a long heavy train operating in an area of curvature - it is called a ‘Stringline’ derailment. - the derailed cars will be to the inside of the curve.
CSX has restrictions about long, light cars on the head end - and some yardmasters fail to follow it.
DPU’s get placed in trains based upon the trailing tonnage within the train.
Thanks. Can happen on model railroads too.
Thanks to everyone for all the good information. So I understand the mechanics of the process I would have to assume that when the train crew shows up for the shift or run someone else has already computed the necessary horsepower and assigned the engines for the crew to use. What I am hearing - do I have it correct the person who put together the trains (title unknown) obtains the manifest of cars showing tonnage and route that the train will travel. He / She calculates the horsepower needed to accomplish the task and then assigns engines from the available roster. DPU are part of the necessary horsepower needed and are placed in the train based on the tonnage and length at a point to eliminate coupler damage. Two questions - 1 - When the maximum horsepower is needed for a small segment of a longer trip does one engine simply get towed until needed are all engines run at a lower rpms, 2 - The calculations seem a bit complicated, do they still use charts or spreadsheets today or this the operation handled by a computer program?
This is an old version of UP’s system special instructions. There have been some changes, but it’s good enough for discussion purposes. Train make up is in Item 5. Within is also the formula for placing manned helpers or distributed power consists in trains.
UP assigns power by Tons per Equivalent Powered Axle. Item 4 gives the EPA and EDBA (dynamic brake) values. It doesn’t have specific TPA requirements for routes, just maximum restrictions for train types. The lower the TPA, the more power required. In my area, Z train Intermodals usually are in the 250 TPA range. Eastbound manifests can be 500 or 600 TPA, westbounds (because of a grade) usually are 430 TPA.
Weather and other conditions can affect operations, they aren’t always taken into account. On that westbound grade, I’ve had trains slightly underpowered, but had no problems in good weather. I’ve also stalled on that grade slightly overpowered in rainy conditions with a temporary 15 mph at the bottom. We couldn’t get our normal run for the hill.
Jeff
Local rail conditions can make a huge difference in pulling power. One fall day I had 100 empty coal hoppers going east from Cleveland on the ex NYC Water Level Route destined for New Castle, Pa. With the wet leaves on the rail, I could barely make 40 mph with 2 4400 hp ac units.
I was thinking that I’d never make it up the grade from Ashtabula, but the leaves there had fallen earlier and blown away, so I had no trouble on the hill.
Some newer units have an air jet system designed to blow leaves, snow, water, etc. off of the rail to improve traction.
Mark
Two questions - 1 - When the maximum horsepower is needed for a small segment of a longer trip does one engine simply get towed until needed are all engines run at a lower rpms, 2 - The calculations seem a bit complicated, do they still use charts or spreadsheets today or this the operation handled by a computer program?
Unless there are manned helper districts - trains are powered to be able operate over the ruling grade without a helper.
The program applications Yardmasters use to switch and build trains provide the Yardmaster a running total of how many loads, empties, tonnage and feet each track in the yard contains. If, say, tracks #1 and #9 are to be the outbound train - adding the totals of each track will provide the loads, empties, tons and length of the train. With those totals Locomotive Management will assign the power for the train. Locomotive Management, on Class 1 carriers have the first and last ‘say’ on power assignment - as they are looking at myriad of issues that Yardmasters and local personnel have no idea about (Quarterly Inspections, Horsepower Hours of ‘Foreign’ engines, Special needs etc.)
On CSX when I was still working - Normal power for all Scheduled Manifest trains was two units Dash-8’s or larger. Normal power for Bulk Commodity trains was two units of the AC persuasion. Intermodals would get three units Dash-8’s or larger. SD40’s & 50’s were used for manned helpers. Four axle locomotives were used for Locals and Yard engines. The effort was to leave Yard and Local power at its use point for most of the 92 day Inspection period. Locomotive Management is responsible for having the engines fueled and serviced with both fixed and vendor fueling operations. When crews get on their trains and communicate with the Train Dispatcher - they will give the fuel status for each engine in the consist. Scheduled trains are also used to pick up and/or distribute power that is or has been shopped.
Needless to say, personnel that are working specific jobs all know what the standards are for the size of trains and power they require as they deal with these constraints every day they work.
Does the length of the train have any effect? A train of coal car empties might be 3 times as long as a loaded coal train of the same trailing weight. But going up a grade with lots of curvature, the longer train might be going thru 3 times the amount of curvature. Would that train need more horsepower even though it’s the same weight?
On CSX - Coal trains are ‘assembled’ at a marshalling location (on my territory the locations were Grafton, WV and Newell, PA. Trains were assembled to be the number of cars the Shipper (Mine) desires to load to the particular Consignee. Power is attached at the marshalling yard and takes the train to the mine and loads it and the moves the train to destination, gets the train dumped and returns the empties to the marshalling yard - or other location as directed by personnel in the Coal Traffic Department. When I retired there were two normal size coal trains - 100 cars and 135 cars. It was rare to double empties together - a high number of the cars used in coal transportation are owned by the utilities that are the Consignees for the loads.
In the real world, when there was a engine failure on a train on the territory, the first place to look was at a empty coal train as most of them could make their destination on a single unit and thus they could give up a unit to the disabled train with minimal consequence.