On the whole, is it always better to have as flat a grade as possible? For example, is it better to have a 1/2% grade for 2 miles, or a 1% grade for 1 mile on a freight rail line?
Murphy,
It is generally desirable to have the lowest possible ruling grade. The ruling grade is the steepest a train and power combination will encounter subject to two conditions. One, the grade has to be longer than the train. Two, it excludes helper territory.
The condition of starting with all of the train on the grade is the most difficult for both locomotives and draft gears. In practice most ruling grades have a slow speed begining, or are several miles long.
Think of DC motored diesels with minimum continuous speeds and associated maximum amperage limits. The amp limits can safely be exceeded for a few minutes, but if the railroad makes a habit of exceeding the amp limit, they will find themselves repairing an inordinate number of traction motors and suffering too many trains stalling on the ruling grade due to motors failing at the most inconvenient times.
In the context of your question as asked, with today’s trains it is probably 6 of one and half a dozen of the other. Assuming no speed restriction at the bottom, the 1% is short enough to be a “momentum grade”, that is capable of being taken by using the momentum of the train to carry it much of the way up the grade. You did not tell us what the ruling grade on the line segment is, but a one mile 1% grade is unlikely to be the ruling grade. A ten mile long 1% grade could well be the ruling grade.
You did not ask, but long uniform grades are preferable to short up and short down grades in succession. These undulating grades are difficult to impossible to control slack action on. The rear end is constantly running in or running out due to the action of gravity on the rear end of the train. Think of a succession of 1500-2000 foot long up and down grades of 1% and running a 6000-8000 foot train over them. Back in the day, the guys in the caboose sat down and hung on while traversing such territory.
Mac
That’s better! at least some of us older folks with poor vision can see it! [X-)]
Two further comments on Mac’s excellent explanation:
- Vertical curves: Using Murphy’s example literally - and assuming level track at each end of the grade - a 1% grade would require a 2,000 ft. long vertical curve at the bottom, and a 1,000 ft. long one at the top (per AREMA recommendations for rate of change of grade to not exceed 0.05% per 100 ft. in sags, and 0.10% per 100 ft. at summits). As a result, the ‘pure’ 1% grade in between those vertical curves would be only 3,780 ft. or about 0.7 mile long (1 mile = 5,280 ft. - 1/2 of 2,000 ft. - 1/2 of 1,000 ft.). For the 1/2 % grade scenario, those vertical curves would be half as long - 1,000 and 500 ft., respectively - so the straight grade would be about 9,810 ft. or 1.85 miles long (2 x 5,280 = 10,560 - 750 ft.).
- The originally proposed Pennsylvania Railroad alignment would have had a steady moderate grade from Harrisburg to the summit just west of Altoona (I forget the exact percentage, but this article says 0.852%: http://en.wikipedia.org/wiki/Horseshoe_Curve_(Pennsylvania)#Construction ). However (following quote is from Wikipedia, but it tracks the Barnard, Roberts & Co. book on this subject): "The line was surveyed by J. Edgar Thomson, who had built the Georgia Railroad. His operating experience led him to lay out not a line with a steady grade all the way to Harrisburg to the summit of the mountains, but rather a nearly water-level line from Harrisburg to Altoona, where a steeper grade (but still less than that of the B&O) began for a comparatively short as
The wikepedia quote that Paul provided is completely incorrect as to the location of the bottom of Charles L. Schlatter’s east slope 0.85% survey of 1839. The base was actually near Alexandria, many miles from Harrisburg. See Charles R. Roberts,
Further previous post.
It is about 150 miles from Harrisburg to the summit. From Harrisburg to Altoona the ruling grade is .4%. Thomson’s choice was 125 miles at .4% plus 30 miles at .85% or 140 miles at .4% plus 11 miles at 1.7%. First cost of the low grade route would have been higher. It would have required more curves and probably taken longer to build. The longer distance at .85% than I previously figured is due to the fact that the route as built climbs at .4% so the difference is .45% or 23.5 feet per mile. The distances are for illustrative purposes only, I did not figure them closely. The .4% ruling grade does not extend for the entire distance between Harrisburg and Altoona.
Mac
Mac & Paul- Thanks for the input. It kind of clears up some of those things I wonder, when I see a rail line, and wonder why the heck they built it that way. I never thought about the ruling grade being loner than the train itself. There is a branch line near me, that is probably from the 1880’s. It goes up and down, following the prairie. The last few years, BNSF has started moving unit grain trains from an elevator at the end of the line. Running a mile long grainer run the roller coaster built for 4-4-0 with a dozen cars must be like a carnival ride.
During the summer months, I write a long, weekly, blog sort of thing about car racing at a local racetrack. I finally figured out, that if I printed it in a little bigger font size, I could see it better to proof read. Some clown always complains that it’s too hard for him to read with the big font. I tell him to try reading small font with progressive bifocals. [|(]
The reason(s) rail lines were built the way they were in the 19th and first half of 20th century(s) were primarily due to the constraints of money, plus construction techniques and equipment.limited what could be done.
The comments about undulating grades and resulting slack action were not that significant until speeds were increased and trains became longer and heavier. Currently, and for the past 50 years, the emphasis has been to construct, or reconstruct, rail lines to minimize slack action since locomotive power is a much more flexible than in the steam age.
The Santa Fe 44 mile line change in the Arizona mountains between Williams and Crookton was completed in December 1960. Westward decending gradient from Williams Jct. is a continous 1.00 % for 31 miles where it then encounters an acending gradient of 0.88 %. A 10,000 foot verticle curve was constructed which resulted in a rate of change in the sag of 0.018. This is one reason the BNSF Transcon is so very efficient in modern operations with 10,000 foot or greater length of trains.
The why do you post is such a small font here?
Murphy, did you ever try proofreading a negative? Back when my company was making and selling LCD watches, I was responsible for seeing that the watches were boxed for sale, and whenever a new module was produced, it needed a new instruction book. I would be sent a negative of the book (about 4 point type) which I would send to a local printer–after I read it to check for spelling and grammatical errors, sent it back with notes about the errors–and then read the corrected negative. It was hard enough with ordinary bifocals.
Well… I’m not consciously typing small… I assume that the font is small, because the system defaults to small, and I don’t think to blow it up? I dunno. Is there a setting on my preferences, that will change the size of print automatically, when I post something?
The other thing, is that my posts on the racing forum can get pre
I always set the size to 3 (12pt), which proves pretty readable, I think. Of course, I also change the font and color, but that’s another story.
As to grades - we have a couple on our line to deal with - Purgatory and Big Moose. Purgatory is shorter but slightly steeper, with some variations (that slight increase near the top will get you on slick rail!). Big Moose hill is about five solid miles of 1%+, but with the curves (there is very little tangent track on the hill) it would probably be compensated higher. I believe the Central used helpers there on occasion, at least in steam days. I know it, too can be a real challenge.
Speaking of vertical curves:
The grade is around 1% on both approaches…
Seems to me the default font size is #3 (12pt). Somehow on your system that has been changed to font size #1 (8pt). I have searched all over the various “settings” features of the web site interface that I can get to and I cannot find any place wherein one can alter that setting.
I am wondering if there is some method of when posting a message the system remembers the last font set by the user. I am going to try an experiment here of setting the font to something other than #3 (12pt) and then post and see if it remembers it for the next posting.
This is in font size #1 (8pt)… and now to click the “Post” button.
And I return to the default font size of #3 (12pt) so it does not remember it on my system.
I might suggest that you clear the cookies in your system just in case that is where the default is altered, though I have no idea how your system would have changed it and stored it in a cookie. Please note, that it is difficult with the usual tools available to the general user to clear just one cookie or just those associated with one web site, and many web sites remember passwords and whether the user was logged-in or out when they last left the site, so if you clear all the cookies on your system, you might have to remember what your passwords were for each of the sites that you are used to just going to and finding you are already logged in.
Another possibility is that if you were to clear your browser’s cache it might correct the situation. How to do that depends on which brand and revision of browser you are using).
Thanks for the advice, but, I’m not computer literate. .
Murphy, I have to remember to make the changes before I begin a reply, or else highlight what I have written and then make the changes. I change the font first (I prefer Times New Roman), and then change the size to 4 (14 point). This size is much easier for me to read than the 12 point. Just click on the font and choose the typeface you like, and click on the size, and choose one that you can read easily.
I haven’t asked for help from a grandchild yet, but, every now and then, a daughter helps me.
I certainly understand… that is why I mentioned the possible problems with the advice.
I am (supposed to be) a computer guru and I regularly bring my computer to its knees or make it go floozy and have to spend a lot of time figuring what I done did to screw it up. It is all too easy to do and often the fix is all too hidden… mainly because I have no idea what I did accidently… even the deliberate alterations I do are sometimes hard to figure out how to undo.
I understand that it is not something that you want, but that doesn’t make it any easier for those of us whose eyes are not what they never were to begin with to read the tiny text. I have tried a dozen things in the testing forum to see if I can cause my system to store a new default and have not been able to do so. I have tried several settings in the various user alterable items in my Profile and Settings areas and none of them have any effect. There has got to be a “simple” fix for you, but maybe it is too simple for us complex humanoids to understand. I will stop muddying this thread with this and contact you via messaging on the site if I ever figure out what can be done… but, please, DON’T HOLD YER BREATH! [+o(]
Semper,
If all else fails hit control+. That will increase the whole page and make small type more readable.
Just take a little air and use some throttle.
Oh, wait, the big roads discourage that, all dynamics these days.
We have a line that resembles a roller coaster. Lots of ups and downs, momentum grades, built prior to the Civil War. Sometimes we go with 2 tons-hp, and get the trains in. On the biggest hill, a long enough train will have the rear end pushing a bit as the head end is going up. Otherwise, speed drops quite a bit with say a 40-60 car train (30 mph down to 15-20). 80-plus cars and the rear end helps push.