I’ve read lots of material on the Pennsylvania Railroad’s Horseshoe Curve in Altoona, PA, and they all cite difficulty of engineering through the Aleghenies.
What I’d like to understand is what specifically dictated that the curve was better than a combination of fill, trestle, cut, and/or tunnel features? What specific engineering “brick walls” dictated this structure instead of something more straight?
Presumably there was nothing specific. They could have built tunnels to get a straighter, expensiver railroad; they could even have gotten a lower grade by starting the climb further east than they did. The added up the up-front costs and guessed at the operating savings and decided it wasn’t worth it.
Which suggests a question…if the PRR was being built (with historic traffic levels) in the 1880’s, 1910’s or 1920’s, would horseshoe curve have been built? If not, what then? A summit tunnel? A different approach and alignment?
Point to remember about rights of way laid out in the 19th Century.
They were laid out by surveyors on horseback who looked upon Irish & German immigrants as being the heavy duty earth-moving equipment when armed with picks and shovels, draft animals as being the heavy duty earth-movers of the period and for them most part black powder as being the blasting agent. Routes laid out had to maintain the desired grade and be attainable within the constraints of the ability to move earth within the economy of the period.
The PRR followed the Juniata river from Harrisburg to Altoona meaning it stayed at the lowest point available until it had no choice but to go under, over, around or through the mountains. The best route had a large valley that would have been impractcal to do anything other than the curve. It also allows more distance to keep the grade lower. The west side of the curve is about a hundred feet higher than the east sde and there are three tunnels at the summit saving another 400 Or so feet of grade.
…And the distance across the two ends of the horseshoe gains {as former poster said}, roughly just a bit less than a hundred feet, and that would not have allowed the 1.8 % grade they were engineerning on avg. up the east side grade to the tunnels which as said before, subtracted several hundred feet more of the climb to get across the summit.
To attempt to bridge across the valley at Horseshoe, {if it would have been possible}, would have added lots of cost and another bridge to maintain. The large accepted curve that adds curcutious distance also allows the accepted designed grade to continue right on up the east side to reach the summit. The curve is even lower in grade {believe around 1.45%}, to compensate it to equal the same needed power around it as other parts of the route to the summit. [2c]
Edit: There was another “curve” near by in another route up over the summit at near the same location. Muleshoe Curve, It was smaller in size but did the same thing in keeping the avg. grade up that route. It’s grade I don’t have the figures at hand. It came up from Hollidaysburg and went thru one of the tunnels at the summit. Was abandoned some years ago. In fact, the “new” route 22 {highway}, cuts thru that former route.
The more interesting question is why the eastward grade over the mountains is 1% while the westward is 1.8%? Restated, why did not J. Edgar Thompson start his westward grade far enough east to get a 1% grade? He could have, the ridges are there to support it.
The short answer is that the heavy traffic was expected to move eastward. If traffic was all loads east and all empties west the 1.8% was fine and no more power would be needed westward than eastward. If the weight ot westward traffic required helper power, then so be it. The thought at the time, 1840’s, was that the extra capital cost of a 1% westward grade was not worth it in terms of operating savings. The PRR had about 60 years, 1850-1910 when they could have built a 1% grade. The fact that they did not is a pretty good indication that the original decision was correct.
Mac
As far as difference between eastward and westward grades is simply from where the bottom of the hill was to the top and how much distance was available to achieve the summit. As for the decision for a horseshoe instead of a straight line grade with bridges and tunnels, you have to understand the engineering knowledge and capabilities as well as construction capabilities of the time. When driving from BInghamton, NY to the NYC area i often marvel at the ingenuity it took to make tracks and canals over and through mountains and streams, work that was done in the 1830’s and 40’s.
Obviously there were many factors but the water level route to Altoona westbound also meant no helpers except for the fiive miles or so to Galtizen. Eastbounds had helpers all the way from Pittsburgh to Altoona is my understanding whereas westbounds were all downhill from Galitzen to Pittsburgh and only needed help for the five miles around the curve.
I see engineering and operational analysis here and it all makes sense. But I suggest that finances entered into the decision.
Almost all initial railroads were built with limited funds and with little or no objective projections about future technology or traffic patterns. There may have been many motivations by those who provided the money but I suggest that they all wanted the most track constructed for the least money.
…and how fast can you build it so the operating bubbas can start to offset the outlay required to build from “A” to “B”.??? The investors want their money back and the managers were under intense pressure to generate a return on investment - or there would be no more railroad expansion. (same story, different era) Add to that, those early locomotives were horribly inefficient, especially in mountain country. (dc and I remember all to well about Raton Pass and the travails of the “Uncle Dick” * and those locomotives that followed)…grade conservation was obsessive for good reason.
*read the early chapters of Jared Harper’s “Raton Pass” or look at Professor George Hilton’s books to see how critical this could be.
The PRR was not called the standarf railroad of the world without reason. First all steel car construction, first to use airbrakes, first to install towers it’s full length and first to construct secondary freight routes so pasenger trains wouldn’t be detained. It also planned a parallel mainline across northern PA called the Sam Rea line to free up the Pittsburgh mainline. Two world wars prevented it from being built so the railroad wasn’t like the UP and cheaply constructed. Horseshoe and the climb was still the best route and was widened to four tracks followng initial construction of two tracks.
ndbprr, My observations were not intended to diminish the status which the PRR (and several other railroads) attained as they evolved. The BNSF Transcon could be described, initially, as two streaks of rust. The same could be said of the CP/UP original railroad that joined at Promontory, UT.
I expect that the PRR evolutionary story would not differ substantially.
Well I would think they’d want the LEAST track built (unless the chief construction engineer was getting kickbacks from the companies supplying rail and ties) since more track meant more upfront costs and more maintenance costs…and more property taxes. However they were limited by the technology of the time. Constructing a bridge might have made sense if the land were flat, but building one on say a 4% grade that would limit the small steam engines of the time to a handful of cars per train would be a poor decision in the long run compared to building a loop to allow for a much gentler grade.
Keep in mind too that before airbrakes were common, a major factor on how long a train could be wasn’t just how many cars you could pull up the hill, but how many you could control safely going down the other side.
It’s certainly true many early railroads were built “on the cheap” with rough-hewn ties and light rail - sometimes they had to build from A to B in a set amt of time to qualify for a government payment - but usually they pretty quickly upgraded their mainlines once trains were rolling and the lines were making money.
“BNSF Transcon”?? Do you mean NP, GN, ATSF or ?? [;)]
I am referring to the line from California, across AZ and NM which is the BNSF Transcon most commonly mentioned as the most efficient and expeditious. Although some say the BNSF has two the north line does not compare in amount of traffic handled.
The Horseshoe Curve was constructed to gain elevation as not to have such a sharp grade. I’m sure they could have tunneled and bridged their way across the gap, but I’m sure it would have been much too costly and building a horseshoe was much more cost affective. I’m not 100% sure on the cost part. This is the basics of the curve others have elaborated more on this project.
-Justin
Please understand the mindset of American railroad building of the early and mid-19th century: ‘build it now, build it fast, build it cheap, we will fix it later.’ The later half of the 19th and very early 20th centuries saw many grand improvements to the American railroad such as the massive rebuilding of the Union Pacific by E.H. Harriman. In 1927 the PRR proposed a new mainline between Lewistown, PA and Adams, IN. The maximum EB grade would have been 0.3%, WB 0.6%. If built this obviously would have obviated Horseshoe Curve but for various reasons, especially cost, the new low-grade line was not built.
Comparisons of western and eastern rr construction are probably invalid. In the west the rr construction over vast distances made the areas habitable and preceded settlers. The east was the populated area getting a transportation system to existing cities and towns and.merchants. Carnegies steel company was in Pittsburgh before the railroad as were the coal mines in central PA and the east coast markets. Different model and different needs and clientele from day one.
The “Curve” was built to be able maintain the 1.8% grade {avg.} as it wound up around the sides of the terrain to attain entry thru the Summit.
The beauty of it was that it was done with only a 9 degree curve at worst and a ruling grade of 1.8%, and could be built by man power without breaking the bank. Ruling grade is really big deal. It drives RR economics pretty hard, to this day. Pretty amazing!
Other RRs built into the “west” at the time didn’t come out so well. The Erie was shorter, but had two major grades. One of them steeper (I think). The NYC was 60 miles longer, doing an end run around the mountains. The B&O was also steeper (and more miles to NY). The PRR route was short AND cheap. A real competitive advantage - to this day!