I’m going preface the following by saying that I realize that there are a number of variables involved with any guessmate so I will try to limit those as best I can.
I was operating a 13-car freight train on my temporary layout this afternoon using two different locomotives: An EMD FTA-B (2,500 HP) and a USRA 2-8-2 Mike. With my NCE Power Cab and some programmed momentum, I used the incremental buttons to slowly bring each one up to speed when the thought occurred to me: “How long would a xx-car train take to reach a given speed?”
So, limiting the locomotives to the aforementioned and using an identical load of cars for each one - in ballark figures:
How long would it “reasonably” take for a 50-car train of 40’ boxcars to get up to 60 MPH from a dead start?
What would the time difference be pulling empty vs fully-loaded cars?
Let me also preface this by adding that the weather conditions are 68 degrees and dry and the track is level and straight.
I hope that helps and that the variables have been limited to reasonable terms. If not, I will try and narrow them down further.
I have my favorite place to watch CN trains, it’s a siding named Midway. I watched SB trains depart, from a stop, many times.
It doesn’t seem to matter if it’s a stack train, or manifest, and using Google maps and the measuring distance feature, by the time the lead loco is about 1800 ft. down the line, it’s moving at 30mph +, and accelerating rapidly.
By the time the DPU passes me, it’s moving at it’s usual track speed of about 48-50 mph., according to the transmission from the nearby defect detector.
This doesn’t have much to do with your scenario Tom, just thought I add what I see.
Interesting question. Some benchmark values for 0 - 60 mph acceleration (unfortunately only marginally relevant to your question):
Bugatti Veyron 2.3 s
Boeing 777 < 6 s
High-speed train 20 - 30 s
VIA passenger train ~ 80 s
Southern Pacific GS-4 with excursion train ~ 5 min
In the video about the GS-4, they did not show the whole train. Thus, I do not know about the tonnage involved. However, I think your hypothetical train would fall into this range.
There are in fact actual answers apart from sarcasm to this kind of question.
One way to get to an approximation that does not involve calculus is to get a drawbar/speed diagram for the power from someone like Ed, plug the numbers for your train consist into the Davis formula to get train resistance, and quickly look at acceleration between a few sets of speed points, say 5mph apart. This will get you within a few seconds of the true ‘smoothed curve’ of acceleration while acknowledging that the diesel ‘part’ will help acceleration down low and the steam engine proportionally more as it gets up toward the peak of its horsepower curve. Note that the corresponding acceleration profile will be very far from linear, with initial acceleration being comparatively slow (limited by the steam-engine cyclic and diesel traction-motor restrictions) and higher speed being more quickly reached.
I have, not counting double track, yards, and industrial sidings, more that a couple hundred feet of track, but none of it is suited for high speeds. I believe the highest posted limit is 45mph, and most trains would be hard-pressed to achieve it before reaching an area with lower posted speeds.
There’s not much in the way of hypothetical performance when grades and curves limit both speed and tonnage. I run some fairly heavy trains, with multiple locomotives, and the hope is that they’ll get from point A to point B without stalling or having to double a hill or two. I find that challenge more interesting than speed, but that’s just a personal preference.
No Henry, I do not have that much space on my layout. I’m talking about REAL CN trains, starting from a full stop, and getting the green light to proceed.
Number of cars. Weight (loads or empties). Grade. Number of engines and what KIND of engines you have. All kinds of variables.
I had SEOP’s (Selkirk-Oak Point) southbound on the Hudson line, 130+ cars, just about 100% loads, 13,000+ tons, with 3 B23-7’s for power (2,200 each). The Hudson line is about as flat as a table top, but you could barely get track speed (50mph) from them after 10-15 miles with a train like that, if at all.
On the other hand, coming home from a run with WNCH-99 (Danbury stone train), 4 engines (usually B-23’s), 40 empties, South Norwalk to New Haven you could zip right along.
Mikes approximation is probably about right for a mainline train. The limits are the weight of the train, the horsepower of the motive power, track curvature etc. as OldEngineman pointed out.
My own layout is a 4x8 so that 1800 feet is about a lap by which time I am doing 30-40 smph. I similarly allow a lap for braking - I’m on DC with inertia throttles with braking control.
What you have to consider is what LOOKS right on YOUR LAYOUT and operating scheme for YOU but well done for asking. Most of us cannot hope to operate in aircraft hangars and have the space for running but a reasonable attempt at trying to emulate what you see will pass for realism … which is what you are trying to achieve,
As Overmod points out there are formulas for train resistance and of course, ruling grade and curvature, temperature and weather conditions all playing a role in getting the train moving.
Another variable I might add is simply —just how quickly does the operating railroad want that train to get over the division and at what risk is there if it doesn’t?
A great deal of operating “lessons” were learned in North America during the high-traffic times of WWII. After the War, of course, equipment was beat, track maintenance was deferred to varying degrees and the railroads were beginning to “see the light” of the coming Diesel age. Some roads, the PRR notably, didn’t have the capital to sink into major steam locomotive repairs.
My point is, some roads were moving thousands of carloads a day along with some spots of high-density passenger traffic. The locomotive assignments (the Power Desk) knew what the requirements of each day’s train was and would try to match power to the train if at all possible.
Mostly this was a redundant task as the makeup of most trains, no matter if a loaded coal drag or a fast mail and express train or even a limited such as the Century, was fairly stable so particular locomotives could be reliably assigned.
The shop forces, engine crews, dispatchers and operators could pretty much know how things were going to play-out during their “trick”. There was redundancy in the trackage for the most part as well with higher speed passenger and mail trains usually run on specified tracks (usually the inner pair) and the slower freight on another. Both the Pennsy and the New York Central could boast a four-track main for nearly their entire routes between Chicago and New York.
This reduced “some” of the risk of, say a poorly steaming engine or a particularly heavy train from delaying the faster trains or “plugging-up” the railroad wit
Plot illustrates train speed vs time (minutes) at max HP of 2500. Train tonnage is 1750T, 35 50T cars. Max usable HP is limited by max tractive effort at low speeds based on loco weight of 247,200 lb and at higher speeds based on Armstrong’s full car resitance chart. This is for level track and full cars.
the number of cars was reduced to 35 in order to reach ~60 mph, at which point train resistance roughly equals tractive effort.
horsepower is 32572 (pounds-force) lbF * ft / min. Drawbar force is HP / speed (ft/sec). while HP may be constant (assumed), the drawbar force dimishes with speed.
i’m sure there are other factors affecting the outcome
Rolling resistance, tonnage trailing, weakest coupler in the bunch, condition of the track, posted limits or work areas where there’s a slow order, meets when the siding one will take is exactly one car longer than your consist without fowling, reports of a bad axle might cause a pucker,…
Tom, it’s a great question, and from the answers it would appear to warrant an entire disseration, or at least a thread. [:)]
I think you must be like me when it comes to running our toys. I set all locomotives to anywhere from 50% of the range for CVs 3 and 4 and on up to about 90%. Northern types with modest trains of 8-12 cars would get the low value, while my Y6-b, I1-sa and 2-10-2 gets the higher value. My practice is to twist my encoder knob right up to my top speed for the track and tonnage and watch everything unfold via digital magic. [8D] My 4-8-4 will take maybe 20 feet and 40 seconds to reach 79 scale mph from a standing start, and my Mallet will lift its tonnage over the same distance, but take 90 seconds, and end at 40 mph.
Without doing any math I was going to say that 50 cars, 2500 tons, would likely not hit 60 mph with that motive power, but would be able to go 45 or 50 mph and get there in about 10 minutes.
The B&O used two Mike’s on 3500 ton trains leaving Baltimore. The ruling grade to Brunswick is about 1.3%. Speeds around 50 were typical from what I have been told.
I don’t care for throttle momentum that has long settings. My Aristo throttles do have a “ramp up” time even when set on 0 momentum, but that is pretty quick, maybe 2-4 seconds from zero to full throttle.
Even on a big layout, our distances are too short for anythi
I know nothing about the physics of this topic, so I will stay out of that part.
I do watch trains in Atlanta and a couple of other places in Georgia.
When NORFOLK SOUTHERN assembles a train in Atlanta, and it leaves the facility, it has a severe speed restriction for the first part of the trip. Then it gets to speed up to 35-40 MPH for a while. Once it clears Buford, it can ramp up to serious speed and tool on down the line.
My question would be how often do train crews really get to open the throttle and accellerate a train at maximum capability? I would imagine this would not be the encouraged way to run a train unless upcoming terrain would make maximum accelleration preferable.
and while i would be interested in what the best approach is, i’m also interested in why. So I specifically asked why max acceleration wouldn’t be best approach.
max drawbar force and hence acceleration is at lowest speed and would be the point that a coupler might break as Ed illustrated and could be limited if necessary (max HP < value below some speed).
i had been told that at least for an automobile, the best fuel efficiency is by maximizing acceleration to get to top gear as quickly as possible. So I’d be curious to know if the most efficient HP for a diesel locomotive varies with speed.
That is untrue. Rapid accelleration results in terrible economy.
This might be true in a foreign country with small cars that have 1.3 liter engines, but with our over-powered American cars, nope.
If you have a manual transmission, and accellerate slowly, and skip the last gear down to get to top gear, you will see a fuel efficiency increase in stop and go traffic. It is a lot of work, and accelleration will suffer. Not worth it.
