I was reading one of my OLD issues of Trains the other day (I sure love those old issues and I’m glad I kept them)…and in one issue from 1975 or 1976 there was a really good article on slack. The article stated that the optimal speed for coupling cars is 4 mph (keep in mind that was over 30 years ago…maybe its a different number now)… any slower than that and you wouldn’t have enough force to couple…and any faster…like 6 or 7 mph…you get into damage to cars and cargo. So how accurately can one control train speed, especially at such slow speeds?
Any slower than 4 mph and they wont couple is absolutely false. Not sure where they came up with that one. 4mph is pretty much an ideal coupling speed though as it reduces your chances of tearing something up.
A good engineer can control his train and pretty much make it go whatever speed he/she wants, weather it’s on the mainline or in a yard switching cars. After a while it becomes second nature.
I’ve been running a lot of trains lately, I enjoy the challenge of switching and controlling large heavy trains. One spot I switch is a yard that is almost entirely on a 1.5% grade. It takes some planning to not allow the train to control you . I also have to drag a 9000 ton-7000 foot train through US customs at 5 mph, quite a challenge because 15 car lengths from the customs office the grade starts downhill at about 1.3%.
Randy
Some hump pushers were equipped with a speed control that could maintain a given speed within 0.5 MPH while pushing a cut.
As with any job, the person doing can do it or get another job. Speed control is important so an engineer has to know how to handle a locomotive and a locomotive with any kind of train under acny circusmstance at any time. I have run locomotives, steam and diesel, but I would never say I was an engineer because I never handled a train.
Coupling I understand can be done at any speed. When to fast, you first damage the contents then the car itself. When too slow, the knuckles may not close and pin may not drop, so you gotta do it again. And again. An engineer has to know his locomotive, his track, and his cars. You’ve got to trust the acumen and skill of the engineer to do it or else.
Watching engineers rerailing cars and engines gives on a appreciation for a ENGINEER’s ability to control speed in a manner that almost defies discription.
A longish video demonstrates the point…
The 4MPH speed limit on coupling may date back to the early 20th Century and probably came from observations that coupling at higher speeds seemed to cause significant damage to the lading. Enforcement was pushed by the railroads’ freight claims departments. Those working in that area would also develop and instruct shippers as to the proper methods for blocking and bracing loads. I don’t know when they first came into use, but shippers experience chronic damage to their loads would sometimes put impact recorders in cars. They could help determine if damage was due to insufficient blocking and bracing or bad handling by the railroad.
In most operations, the train or engine speed is left to the skill of the engineer, but locomotives can be equiped to automaticly control the train movement at a very low speed. I have seened these use for “in motion” coal unit train loading. Perhaps there are other uses.
Many older locomotives may not have had a speedometer, certainly I know that older subway equipment never had them. Locomotive engineers used to time their trains with a stop watch between mileposts. On subway trains, you just had to know what you were doing, because speedometer or not, the company was still out there with their own stopwatches and later radar guns.
On the R1s to R9s you could tell the speed by the musical pitch of the bull gear, if one could tell tones in the first place.
ROAR
“Slack - difficulties and problems of slack”
by Hilton, George W., from Trains, February 1976, p. 22
(Magazine Index keywords: coupler operation slack )
Fairly lengthy article, as I recall.
I believe author Hilton - who was slightly out of his native element, as he’s an economics professor, not an engineering type - was referring to 4 MPH as being the optimum coupling speed for a free-rolling car as in a hump yard or a ‘kicked’ car in a flat switching yard, not for a coupled locomotive and string of cars moving against a standing car, etc.
Norfolk Southern has a ‘gradation’ of tolerances on maximum speeds before the engineer is in violation and penalties may be imposed, and I think that speaks to the subject. I don’t have a copy in front of me, but it’s something like +/- 2 MPH for speeds up to 20 MPH, and then roughly +/- 6% of the max. speed up to 50 MPH, then a flat +/- 3 MPH above that.
- Paul North.
The only rail non tranist equipment I knew of without speedometers were the DL&W MU’s. Everything else on the railroad, with very few exceptions…perhaps by the individual unit rather than whole class. Where there were no speedometers were probably in switching duties or where there were governors.
Very — I’ve watched passengers cars coupled and uncoupled to / from live trains with the stationary car never moving as the couplers drop into coupled position. There have been several articles about how various trains switched at night would never jostle the sleeping passengers.
We knew who the good hump engineers were, because they could maintain a steady speed when shoving a cut of cars over the hill (keep in mind that the tonnage they were shoving became progressively lighter).
As a Car Retarder Operator, I was among the first to really appreciate remote-control operation of the hump engines, because remotes maintained a steady speed. Once the remotes took over, it wasn’t hard at all to know when an engineer was doing the shoving on an extra job or something–none of them were as good as the remote operators.
Humping speeds are often measured in tenths of a mile per hour. It’s very exacting. I don’t remember what the precise speeds were, but I certainly knew when they were strayed from!
Speaking as someone that probably does near 50-100 couplings a night, generally, the gentler you do a coupling, the more likely the pins will drop. You hit em at 3-4 mph (maximum allowable safe coupling speed), half the time one of the pins won’t drop. Stretch em, and try again at a slower 1-2mph speed, and you get instant pin droppage.
Plus I enjoy a perfect eggshell coupling. Much better than a birdie coupling.
Now if you could only convince your conductor that cars are not 30 ft. long.
Had an engineer come in one time to recouple the engine to the rest of the train after the runaround we do at each end of our trips. He was very proud of the fact that he hardly made contact with the standing car. Problem was, it was so gentle that the pin didn’t drop at all.
I backed him up and had him come in a tad harder the next try.
And then there are the engineers that really like to plant 'em… [:S]
Outside of switching, maintaining a given speed is a matter of knowing your train and the profile.
My usual territory includes up to 1% grades, some 5.5 degree curves, and a couple of permanent slow orders. From the highest point to the lowest is a 200’ drop over six miles, but it’s not a constant grade.
I try to hold a consistent speed, but it’s not always easy - particularly because few of our locomotives have dynamics, so it’s all done with brakes and throttle. Sometimes you can get lucky in certain sections and be able to ride a set for a fair distance, and sometimes it’s all you can do not to p*** away your air.
“birdie coupling” ?
Probably 1.0 to 1.3 MPH or so for single pin-puller who walks holding up the cut lever at about 2.0 to 2.5 MPH - half that speed gives him/ her enough time to get back to the starting point just as the next typical-length car’s coupler arrives. If there are 2 pin-pullers, then the humping speed can double to 2.0 to 2.5 MPH or so, and they can take turns, each getting the alternate cars.
[:-,] Much faster than that, and then pin-puller will have to start jogging to keep up with the speed of the cut being humped (but running is against the safety rules most places). And, you’ll then need a total of at least 3 and maybe 4 persons - pin-puller and 2 more walking back after their jog, plus 1 resting up for the next sprint ! [swg]
- Paul North.
One of those couplings that you look up at the birdies instead of the carnage about to unfold in front of you…
I gotta summarize this to see if I understand it.
The speed control of a locomotive is just a nine position switch; 0 for Off, and positions (or “notches”) 1 thru 8 for eight distinct throttle values. There is no “notch 3.67” for some speed inbetween whatever speed is produced by notch 3 and notch 4.
But these throttle positions are not settings for a specific speed. The actual speed will vary, based on the resistance of the train to movement, things like grade, curvature and wind resistance will slow the train from the “free wheeling” speed that the locomotive by itself might do given the no load speed of the electric motor at a given voltage supplied to it and the gearing between it and the wheels and the wheel diameter. The voltage supplied is controlled by the speed of the Diesel engine driving the generator and it is the speed of the Diesel that is controlled by the throttle.
But, because the throttle has finite positions and no intermediate positions it seems the Engineer would have to constantly adjust the throttle between two positions to maintain a specific speed if that speed was not attainable at just one notch. And maintaining a particular speed at one notch seems pretty much an imposibility given the variances in rolling resistance of the train (grade, curvature, and wind, etc.).
I know that inertia will dampen any rapid change in speed, but (given my possibly erroneous understanding above) on average, how often does the Engineer have to adjust the throttle to maintain any particular speed? And, to reiterate the original poster’s question, how close can the Engineer hold the train to the desired speed?
Yep. Skill of the engineer and/or the accuracy and ability of the onboard computers.