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The difference between 40 mph and 55 mph?

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[quote user="gabe"]The answer to this question may very well be, I am just too much of an amature to ever properly grasp this question.  But: I grew up along the former Wabash in Souther Illinois (Decatur to St. Louis).  That line has always had a reputation as a bit of a race track.  As there is a long stretch of highway that goes along side the track near my home town of Mt. Olive, I have had ample opportunity to clock the speed of freight trians.  Road railers regularly run at 65 mph and probably average 55 mph.  Most manifest freights average 50 mph but I have seen 60--and on very rare occassions 65.  67 mph was the record, but that was about 15 years ago. Anyway, I have walked that line 1000 times and am familiar with rail lines around here (Indiana) that are only rated for 40 mph.  For the life of me, I cannot determine the difference between the Wabash main of a 65 mph speed limit and some of the 40 mph track I see around Indiana.  In many instances (INRD being a good example) the rail head is actually heavier on the INRD than it is on the Wabash.  I am fairly certain the Wabash rail head is 120 lbs, whereas much of the INRD is 136 lbs (also largely welded).  To further complicate the picture, I was reading a book about a shortline that bought the old Erie main in Northern Indiana.  That line was rated at 110 mph! according to a book about the INRD (this was back in the late 70s-early 80s).  Surely, given the neglect of the Erie, it could not have been in better shape than the current INRD? Also, there are a lot of old ties on the Wabash main.  The Wabash main seems to have some more ballast, but not what I would think would be a noticeable difference.  Finally, if the curves on the old Wabash main are super-elevated, it is lost on me. What is the difference between rail rated at 40 mph and rail rated at 65 mph. Gabe[/quote] Some of the factors that determine train speed: 1.  Method of operation.  FRA regulations require a block system of operation (manual or automatic) to exceed 49 mph for freight, 59 mph for passenger.  (Note -- you do not have to have signals, as is commonly assumed, to go faster than 49 mph, just a block operation per 49 CFR 236.0.  KCS, for instance allows 55 mph in dark territory on the L&A between Meridian, Miss., and Bossier City, La., because it uses manual block). 2.  Track class.  FRA permits 40 mph (freight) for Class III, 60 mph (freight) for Class IV, 80 mph (freight) for Class V.  The differences between class is how much money you want to spend.  Higher speeds have less tolerance for wide gauge, deviation from alignment, cross-level variation, runoff (variation from vertical alighnment), and condition of ties, ballast, rail, joint bars, and turnouts.  Size of rail is not prescribed.  A very good "users manual of track" is found at http://www.fra.dot.gov/downloads/safety/track_compliance_manual/TCM%205.PDF (143 pages, beware). 4.  Rail weight is something that goes hand-in-hand with high average axle loads and high gross ton-miles, not so much high speeds.  115-lb rail is perfectly good for high speeds. 3.  How fast do you really need to go?  Higher speeds require more fuel and greater expense for track and rolling stock maintenance.  For many lanes and types of freight higher speeds diminish profits.  There is no point in racing to the interchange and arriving at 1700 instead of 1800 if the connecting railroad only picks up once a day at 2400.  Chasing minutes out of the system is very hard because it is a "tail wagging the dog" type of iteration that tries to bend the performance of the entire system to the performance of a single element. Railroads spend a lot of management time choosing the speed that gives the best results (profit) for the traffic mix given limitations on capital expenditure, demands for profits by the shareholders, etc.  As for historic cases, axle loadings were generally much lighter, labor costs were much lower, and passenger service demanded higher speeds.  In some cases track capacity and train-speed conflict difficulties mandated higher speeds for freight, too.  I do not have the book in question that you recall saying the ex-Erie main line in northern Indiana was still good for 110 mph in the 1980s and am skeptical that was indeed what the track was still good for.  Given the sketchy nature of that "fact" I would set it aside. S. Hadid
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