train weights

To figure horsepower requirements is the scale weight of loads and the lite weight of all cars totaled to get the tonnage of the train?

Generally, yes.

The gradient (profile) of the route involved has to be considered when figuring the hp requirements. Also, the type of train and the desired average speed.

On today's Class I's, and many smaller railroads, the weight of each carload is immediately available - the tare weight through UMLER and the lading weight through ISS. Simply entering the car numbers will yield an accurate weight of the train. In those instances where the rate is not made on weight, but on a per car basis, it is assumed the shipper loaded the car to its load limit, or in some cases, an average of that commodity over the scales at major hump yards.

Some systems are sophisticated enough to assign available power to the train weight. One less job for the Trainmaster.

Just to add a bit to what third rail said... railroads are doing what they can to discourage weighing cars. Scales are expensive to install and service, and are time consuming to use, even those that are weigh-in-motion. A lot of product moves on a Shippers Weight Agreement (SWA) that is a sort of gentlemen's agreement between between shipper and railroad that states that the shipper will load X tons in their equipment. Quite a few large shippers actually invest in their own scales. they use the weights for billing purposes with their customers.

Just to add a bit to what third rail said... railroads are doing what they can to discourage weighing cars. Scales are expensive to install and service, and are time consuming to use, even those that are weigh-in-motion. A lot of product moves on a Shippers Weight Agreement (SWA) that is a sort of gentlemen's agreement between between shipper and railroad that states that the shipper will load X tons in their equipment. Quite a few large shippers actually invest in their own scales. they use the weights for billing purposes with their customers.

How much horsepower is needed per ton of train, per 1 degree of grade for something like a coaldrag.

According to my copy of "The Railroad - What it Is, What it Does"
by John Armstrong, you need roughly 2 hp/ton to go 30 mph on
a 1% grade, more than 1 hp/ton to go 20 mph, and less than
1 hp/ton to go 10 mph, on the same grade.

But you'll start pulling knuckles if all of your power is on the head
end and your train weighs more than about 10,500 tons on a 1%
grade - so you either limit to 10,500 tons and provide two or three
4,000+ hp units, or you use DPUs to push-pull a heavier train.
Coal trains can be 18,000 tons or more in some territories.

UP and BNSF often pull PRB coal trains with one or two 4,400 hp
units while pushing with one more similar remote unit. BNSF
runs some coal trains across Iowa with only one unit at each end.
I'm not sure what the ruling grades are on these routes.

- Ed Kyle

Yes. In the case of the Southern Pacific their formula was 3.5 horsepower to trailing ton.