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I've asked around on this one, but haven't gotten an answer so I am trying here, too:

There is a subdivision I run on that has a ruling grade of 1.1% eastbound. The tonnage ratings for that same subdivision are less for westbound trains than they are for eastbound trains, which have to contend with the ruling grade. I would have assumed the tonnage ratings would be less for eastbounds than westbounds; that's the case for every other territory I run on.

Of all the subdivisions I operate on, this is the only one with this scenario. Can anyone explain why this may be, or if there is another piece of railroad someplace that has a similar setup?

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There is a subdivision I run on that has a ruling grade of 1.1% eastbound. The tonnage ratings for that same subdivision are less for westbound trains than they are for eastbound trains, which have to contend with the ruling grade. I would have assumed the tonnage ratings would be less for eastbounds than westbounds; that's the case for every other territory I run on.

If that is the case, common sense would say that the westbound ruling grade is steeper than the eastbound grade. Along with that, there could be sharper curves which translates to more drag going WB. This is the way it was on my district.

The rule of thumb we used was that every degree of curvature was equal to 0.1% of grade. So a 10 degree curve was equal to a 1% grade. It depends on how old your railroad is. More modern railroads were compensated for curvature. On a compensated railroad, if a train is going up a 1% grade and enters a 5 degree curve, the grade will reduce to 0.5%.  This way the locos will see no difference in the load on the drawbar. If the railroad is older and not compensated, the grade and curve resistance would add together resulting in an effective grade of 1.5%.

Last edited by David Johnston

I didn't know about compensating grades on curves, that's pretty interesting.

As for the original question, it still doesn't make a whole lot of sense to me that while the steeper grade is eastbound, you are more constrained tonnage-wise while going westbound. Not too many sharp curves or anything to account for the difference, it's a 79/55 mph subdivision except for some 70/50 curves.

If the ruling grade is 1.1%, it is actually 1.1% compensated, as used in tonnage rating charts.  This is universal.

No railroad grade is completely steady.  There is always some vertical curvature which causes small variations.  Curvature is the main factor in compensating an ascending grade for tonnage rating purposes.  The Engineering and Mechanical Departments run their numbers and the tonnage rating is produced for each class of locomotive, and sometimes with variations for train length.  Then it has to rub up against helper placement rules, long car/short car rules, train tonnage placement rules, etc. in order to get a train over the mountain, and you know how that works, since you do it daily.

I suspect that the curves are more numerous, or tighter, or longer -- or some combination of the three -- on opposite sides of the crest of your grade.  Is there a difference that you can detect?  It only takes one 10-degree curve to change the rating for that whole side of the hill.

Speaking of curves, there was a ten mile stretch of track between two towns that followed a river. As we rode along downstream, after leaving one town all you needed to do was get the train over a slight grade and then you could shut the throttle off and pretty much coast at track speed around the river to the next town. With a normal mile long train or so, you didn't notice any speed differential going around the river. However, one day I had a short train of about twenty five cars. After getting over the hump, I just let the train drift along. On this day it was very noticeable that every time the train went through a curve you could feel it slow down just a bit due to the drag from the curvature. Then as the track straightened out, the speed would pick back up just a bit. The train did that for about nine miles and that was the only time that I ever noticed the drag from curves.

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