I’m building an N-scale layout and want to add superelevation to my curves. I do plan on having the curves on level ground superelevated, but I do have a doubletracked section on a 2% grade, and a single-tracked section on a 3% grade. Do prototype railroads superelevate curves on grades?
Curves are super-elevated to match either the fastest permitted speed on that section of track or the normal freight train speed. The latter is the usual option, since it minimizes rail wear when the forces are balanced. Whether or not the track is on a grade is irrelevant.
It should be noted, though, that model railroads have much shorter vertical curves than the prototype. I don’t know if changing super-elevation at the same place as a rapid grade change will lead to problems; my guess is that it should not alter the situation.John
Prototype railroads superelevate curves on grades. Since train speeds are often lower on grades, the amount of superelevation can be less compared to curves where there is no grade.
Mark
It is dependant on traffic and speed, but in a nut shell, Yes. On mainlines, and medium to heavily trafficed branchlines superelevation is (was) used. On low traffic/low speed branch lines suoerelevation would likely not be found as it adds a great deal to design and construction costs, and is of no benefit at low speed.
You mention grades on your pike of as much as 3% which would be considered quite steep for a prototype mainline grade. The type and speed of traffic should determine whether superelevation should be used. If you run through passenger, or other high speed trains on this grade, you will want superelevation on curves.
Prototype railroads did have fairly steep grades on their mainlines, and dependant on usage utilized superelevation. A good example of this is shown in many historic photos of B&Os Cranberry grade. Much of this three rrack mainline grade is 2.2%, and superelevation is descernable in many of those photographs. The traffic on this grade in the days of steam consisted of everything from 54 car coal trains powered by three locomotives (one pulling and two pushing) at 15 miles per hour. To the sleek and speedy 5 car Cincinnatian daytime passenger train pulled as fast as a P-7d streamllined 4-6-2 could go. The coal trains would have experienced no benefit from superelevation while ascending such a grade, but the faster trains certainly would. All trains would benefit during descent, as speeds would be higher down grade. Many western mountain crossing lines had grades as steep or steeper than that of the B&O, and would have used superelevation if high speed trains used their lines.
The main benefit for superelevation of curves on a model railroad (given our larger than scale flanges and such) is visual interest. One of the most important aspects for superelevation both model and prototype is to make it gradual, not a sudden lurch upward (or downward). One way to accomplish this is with successively shorter lengths of masking tape (I use 1/4" wide in HO which might work for N since anything narrower could be a challenge to work with) on top of each other building up to the height you want. Don’t overdo the height — even modest super elevation gives the visual effect you want.
Of course you do not want a huge gap showing under the rails and ties so super elevation calls for careful ballasting of track.
ADDENDUM TO POST. Here is a live link to the (really neat) photo Andy Sperandeo points out
http://users.snowcrest.net/photobob/sfa22.jpg
I might add that there are also lots of photos from the Pennsy’s Horseshoe Curve showing Class J 2-10-4s leaning to curves both up and down grade. I repeat from my main post however that it needs to be gradual. The prototype has train brakes and other techniques for going downhill into an easement curve but if the super elevation is too abrupt when N scale (or HO) cars are bunching up, there could be some problems. It does not take much super elevation to get the visual effect which again is mainly what you are after.
Dave Nelson
Hello “Red,”
You can go to http://users.snowcrest.net/photobob/sfa22.jpg to see a picture of a train climbing a 2.2 percent grade on a superelevated curve of about 10 degrees, which is fairly sharp for a prototype main line.
So long,
Andy
I’d assume even on a double track main there would be occassions where a train might have to descend down the grade on the “wrong main” so you’d want to have some superelevation on it(??)
hi Stix,
Doesn’t make any difference. Both tracks had super elevation. Going up or down is not the issue, running right or left neither; as long as the inside track of a curve is lower then the outside track.
Paul
My friend who actually worked in track service for a real railroad always points out that in practice, the outside rail was raised.
If in doubt, go to the prototype for guidance. The following is from a narrative about the BNSF’s new construction in Abo Canyon, one of the bottlenecks on the route from the West Coast to the Midwest. The track in the canyon twists and squirms its way down, paralleling the watercourse at the bottom of one of the very few breaks in the escarpment between Eastern New Mexico and the Rio Grande Valley.
Track speed (designed, and existing on the present single track) is 40mph, due to curvature. The new track will be superelevated 3.5 inches…
Not specifically stated, but I presume that the existing track is superelevated to the same standard.
3.5 inches of superelevation can be closely approximated by raising the outer ends of the ties 1/16 inch for HO and 1/32 inch for N scale.
Chuck (Modeling Central Japan in September, 1964 - with superelevated curves)
As with anything prototype, yes and no. The common misconception is that any curve needs to be superelevated just because it is a curve. But superelevation has only one purpose and that is to compensate for the speed derived centrifugal force of a train moving around the curve. Without significant speed, it is counter productive to superelevate a curve. Doing so would transfer too much weight to the inner rail of the curve and too little to the outer rail thereby causing accelerated track deterioration and creates an unsafe condition for slow speed or stalled trains.
Now the transition from level track to grade is known as a “vertical curve” to ease the transition and protect cargo and equipment and to maintain coupler alignment. This is a rather simple calculation taking into thought the minimum length of vertical curve in feet, the train speed, the absolute value of the difference in grades at the point of intersection of the vertical curve, and the vertical acceleration in feet per second (this gives you the actual value of what we as modelers call the “%” of grade and is based on a whole bunch of other variables). Actual on site construction is done with a pencil and paper as each curve has a unique aspect based on the terrain on site, but it’s simply calculated on the basis of a parabolic curve.
A couple of things to look for in pics of the subject are:-
- Heavily built up ballast shoulders - mainly or only on the high/outside rail side. These may rise as high as the rail head - but will be clear of any low slung equipment that will pass on locos and stock. They may extend further from the rail than standard ballasting… i.e. the cross section of the ballast profile will be wider. They may cover the ties right up to the rail. Any combination may apply.
- Track and rail stabilisation. You are looking for signs of track anchors - usually attached to the ends of the ties… usually the outer (high side) ends. The purpose is to prevent the track being shoved out sideways. You re also looking for rail anchors - in this case they would be fitted to the up hill side of tiies to the bottom of the rail. These are to prevent the rail creeping downhill. Eve in H0 you wouldn’t actaully model these 'cos they are way too small BUT you might want to represent new ones with tiny flecks of paint… when new ones are installed they really do showup bright. You don’t need to do a whole lot… they get replaced in ones, twos and groups as required. A length of new rail (different colour from surrounding rails) would have all new anchors… the
I have never seen a “track anchor” in the US. In US practice there is nothing attached from tie to tie other than the rails. Sometimes they put a nail plate on the end of a tie (a galvanized metal rectangle with little holes in it) but that is just to keep the tie from splitting.
Rail anchors are attached to the rails and placed next to the ties on both sides of the tie. Concrete ties don’t use rail anchors because the clips serve the same purpose.
Ballast above the tops of the ties is a waste. It does nothing to stabilize the track. The ballast between the ties and off the ends of the ties keeps the track in place.
Actually they do knock the anchors off the old rail and reuse the same anchors. Unless the rail is a different size and they need different anchors they will reuse the same spikes and anchors. Unless the rail is being scrapped and loaded in a gon, they would have to take the anchors off of it to transport it.
Dave H.
What I failed to include in my previous post (about the 3.5 inch superelevation on 40 mph curves in Abo Canyon) was that that would result in a 3" overbalance - a train running 40MPH would need 6.5 inches of superelevation to be exactly balanced.
Note that 40 mph is a MAXIMUM speed. A stopped train would be overbalanced 3.5 inches toward the inside of the curve.
That said, model superelevation always results in an overbalance to the inside, unless you operate at a (scale) speed measured in Mach numbers. Speed scales, but the laws of physics don’t.
Chuck (Modeling Central Japan in September, 1964)
I used 1/8" striping tape from the hobby shop for this on my HO layout as it flexs on a curved line. This is similar to what Bill Darnaby and others do with layers of masking tape. I start about 5 inches before the start of the curve under the outside rail and lay the longest tape to the other end of the curve also 5 inches beyond the curve. The next layer on top of that is shorter, starting about 5 inches from the ends of the tape underneath it. I continue the process until I get to the height I want on the outside rail. Each next layer of tape will get shorter. I don’t go above 3/32" in height and lay my curved flex with spiral easement on top of the built up tape. I use the usual method of a caulking glue to tack down the flex but avoid getting anyone btw the tape the ties. I must add that my minimum radius is 30" and it works well even with finicky brass steam locomotives. I had the striping tape on hand from railroad maps I make for publication but, of course, masking tape would be cheaper.
About all my curves are on a grade to a max of about 2%. I am pondering what to do about a couple that enter or exit a helix. Obviously, I don;t want to superelevate the track in the helix but am going to try easing in and out of a curve on superlevation entering or exiting the helix.
Hmm… I’ve never seen a US example either but I would be amazed, astounded even, if there were never, ever any examples of devices being used to encourage track to stay in place. The laws of physics and human ingenuity apply everywhere. Between the heavy loads of Class 1s and mad conditions of logging lines I would expect someone to have got up to something. I recently saw some mainline (UK) track “assisted” to stay in place by baulks of timber across the 6 foot way between the sleeper ends (tie ends) of adjacent tracks. One line also had a specially designed channel girder in its four foot keeping everything in place lengthways. Okay,not the USA but I’d exoect US engineers to come up with similar solutions in places that the track didn’t want to behave nicely. As far as modelling goes all I’m suggesting is that people look out for unusual features like this to add interest to their layouts. of course,if the things aren’t there in the pictures… then they aren’t there to be modelled.
[quote user=“dehusman”]
Rail anchors are attached to the rails and placed next to the ties
Dave-the-train: I really respect your enthusiasm and willingness to share. Could I suggest you get either a copy of the AREMA recommended practices, a North American Class 1 railway track maintenance manual, or a standard engineering text such as Hays. I think you would enjoy and value how it would greatly expand your knowledge of track structures and maintenance practices.
I’ve worked for railways that follow the British model as well as the North American model and found the practices to not be significantly different than the North American model, with the exception of maintenance being much much less robust because our axle loads were so much lighter, and much more costly because costs were being paid by someone else so the culture had over time acquired a cost-no-object mentality.
RWM