Well let's ballpark it
Amtrak Superliner cars weigh 74 tons
http://en.wikipedia.org/wiki/Superliner_(railcar)
17 of them would be 1332 tons
add maybe 200 tons for a diesel electric locomotive
though they can easily be twice that
http://en.wikipedia.org/wiki/GE_AC6000CW
and we're around 1500 tons.
40 mph is 58.7ft/sec, call it 60
so on 1% grade the 1500 ton train is dropping at rate of 0.6 ft/sec
which is 1500tons X 2000 lbs/ton X 0,6 ft/sec = 1.8e6 ft-lbs/sec ,
divide by 550 ft-lbs.sec / hp = 3272 hp
rolling resistance of rail wheels should be in range of 0.002X load,
http://en.wikipedia.org/wiki/Rolling_resistance
3 tons for this train
so we'll subtract that work
3 tons X 2000lbs/ton X 60 ft/sec = 3.6e5 ft-lbs/sec ,
divide by 550 = 654 hp
subtract that from 3272
leaving 2618 hp, or 1953 kilowatts available .
Interesting.
Remember that railcar couplers are not rigid but have a little bit of travel called "slack action".
Back in the dark ages when i rode locomotives the engineers preferred to keep the train stretched out so as to avoid that "clunk" when the couplers moved,
If you let the train compress when starting downhill, the last car gets a "whack" because the front of the train is already moving slower than the rear when the slack gets all used up, so the last car must decelerate quickly. It's like cracking a whip. You'll hear it in slow moving trains in switchyards or at crossings, a loud crash that progresses down the row of cars when engineer reverses direction .
So, in order to give his passengers a comfortable ride the engineer might waste a bit of that kinetic energy in order to keep the couplers in tension .
He'd apply the train brakes which are separate from the locomotive brakes,
Train Slack When running a long train, slack enters into the equation when talking about train control. The old saying goes, "either you control slack or it controls you."When two cars are coupled, there is not a rigid connection there. There is space within the coupler which closes when you pull on the car, and opens when the train in front of the car is going slower than the car is. Many modern cars also have cushion couplers (of different names). When the car is coupled, or slack is run in, the coupler has a shock absorber to avoid damage to the freight, or discomfort to the passengers. These couplers add to the amount of slack in the train...On short trains, like your typical 5-10 car local freight, slack isn't much of a concern. On passenger trains, and long freights, it is something you have to always consider.
A hard "run out" of slack will break your train. The coupler or draft gear will break, and your run will be over until you fix it. This is not a good time to find out you're on bad terms with your co-workers... A hard "run-in" of slack, at best, will make you feel like the locomotive was rear ended by a train, and at worst will cause cars to derail. ...
.....
Using Locomotive or Dynamic Brakes: When train make-up and road characteristics require slack to be bunched, reduce power gradually to allow slack to drift in. Continue to bunch slack by gradual use of dynamic or independent brake.
A quick or heavy application or the independent or dynamic brake will reduce the speed of the [front of the - jh] train more rapidly than the rear. This will result in a slack run-in which can be quite severe. This can cause a rapid heavy buff loading on the rear units of the consist and could cause them to jackknife.
To avoid sliding wheels, dynamic and independent brakes can't be used at the same time. When train brake and dynamic brake are used at the same time, press / to release the locomotive brake. The standard range dynamic brake develops its maximum retarding force between 6 and 23 MPH. Dynamic brakes must always be applied and released gradually.
...
http://www.ovsrails.com/OVSTI/AdvancedTrainManual.html
