Who makes the decision as to the number of Diesels needed for a consist? Is it based on gross tonage?
Norm
At a Class I railroad, the decision is made by the power dispatcher at the railroad’s dispatching office. At a very small railroad, the decision might be made by the engineer of the train. In between there is a variety of methods.
The first requirement is provide enough power to get over the route without stalling. The second requirement is provide enough power to meet the service requirement. Class I and regional railroads operate almost all trains according to a service plan that describes how many horsepower per ton each train is to have: trains with higher levels of service get a higher horsepower per ton, e.g., a coal train might get 0.8 hp/ton while a premium-service intermodal train might get 4.5 hp/ton. Assuming there’s enough power available, that’s what the train gets.
RWM
most generally when i get my paperwork for the train i have that day if i dont have enough power i call the yardmaster or trainmaster and they either fing more power or cut the tonnage so i can pull it. there is one other thing they try and do is make sure it has enough power to get all the way off the division, once that happens they dont care if the south end has enough power that becomes thier problem( yep pass the buck). On certain trains they make set outs and pick ups and everyone watches the tonnage from the clerks to the dispatchers and the crew, If you slip down due to over tonage The first person in line for disapline is the crew starting with the condutor then the engineer and on up the line.
I assume that the current method is the same as it has been since diesels were first used. The builder provides a series of graphs to the railroad that indicate tractive effort and tonnage for various percentages of grades. The railroad then generates a tonnage rating for the lcocmotive for each division or branch on which it could operate. All employees who need this information are given copies and the horsepower assigned is based on this information. But there are some caveats. A section may have an uphill grade the entire way in one direction and be downhill in the other so more HP is needed to go up then come down hence more engines needed in one direction then another. So you may see some engines just coasting along to be returned to the direction they are really needed. Some dispatchers will overload a lashup figuring there is a cushion in the tables and the engines are really capable of pulling more than the table say’s. Other times a train may have to double a hill because the sufficient power wasn’t available or there is really only one serious location requiring more power and it is easier and cheaper to have fewer engines take the time to pull up the hill what they are capable of and rejoin the train for continuation of the journey. The Iowa Interstate encounters a pretty serious hill going east from Joliet illinois to Blue Island around New Lenox coupled with a Metra station right at the base of the hill that they have to avoid blocking access across the tracks makes them sometimes have to stop or slow down considerably until the people have all crossed over before climbing out of the valley. Every engineer I have talked to complains they are underpowered but they do always make it without doubling the hill. I guess it is similar to getting on the interstate with a Yugo or a Ferrari. in one case you have to pedal with all you have so you don’t get run over and the other you barely have to touch the acceler
From my vantage point working as an Assitant Chief Dispatcher (ACD), the various locomotives we have are rated based on their horsepower and the route. For instance an SD40-2 can pull a lot more tonnage on the flat water-level route than through a region with several ruling grades such as we see in hilly and mountain regions. Some trains are profiled to run across the system and can be consisted from orignation to make the entire trip with the same consist. Other trains may have to add or cut power as they make an intermediate terminal. Most of those decisions are made by the Power Bureau at HQ. I’m allowed to make suggestions and even variations as long as I keep the “power people” in the loop.
With as busy as RR’s are lately there is almost always a shortage of power. I may end of having 300 Avons sitting in E. St. Louis with only 2 SD-40’s to pull them. The tonnage for the 300 cars may be 20,000 and the SD40’s may only be able to handle 10,000 tons of that. And of course the tonnage ratings are based off units in good working condition. You learn really quick not to push trains to the limit. When possible I like to leave a little bit of working room because you never know when an engine may not be loading properly, etc. And setting out on the line of road just creates all kinds of new problems such as blocked sidings, etc.
And even though an intermodal train may not be very heavy we always leave the premium units aside for those trains so that they make track speed no matter what grade they encounter as they are on tight schedules, and keeping UPS and CO. happy is priority #1!
There is the matter of Coupler strength.
You have to stop adding engines after a certain level of force is reached on the couplers.
There is the Terrain. A mountain requires X horses to LIFT the train up and OVER the height. The amount of work that can be done in a X amount of time depends on availible power. I can lift 40 ton with a 350 big cam 4 20 years ago on a 4 mile grade of about 5% at 18 mph and however long it takes me to get to the top. 10 years ago that same weight can be carried over the hill with better transmission but same horsepower at 32 mph. When I stopped, the 500 Detroit could run at 45 up and over in a few minutes.
Technology plays a part, the “Good” engines will haul the important trains the rest get what they get. You dont want to put top of line units drinking X dollars in fuel sufficient to wipe out a revenue from the train it’s trying to pull. Not worth the effort. Now if the units went onto a high dollar train and is profitable… yay!
Another consideration is the amount of power needed to maintain a speed. You might not want a train to lug down too much and stall or find yourself unable to generate retard braking on dynamics on the downgrade.
And finally, a scheduled time train requires more horses to finish the trip in a short time. All other trains get what they can.
In the 50’s I see photos of railroads adding engines… 5, 7 or more until the train moved. It may have taken everything a yard has in the roundhouse but they moved it out.