Prototypical Question: Factors Influencing Speedlimits

LAST EDITED ON Jun-04-03 AT 08:13 PM (EDT)

I've got some questions regarding prototypical speed limit policies for various train types, weight and other factors that might have an influence on permanent speed limits applying to a trainDear fellow simmer community,Some questions and thoughts regarding North American RR operations have accumulated with me over the past few months of exploring US routes and rolling stock in MSTS, among them the following one regarding the existence of “variable” speed limits. As I am not at all familiar with the details of operations and methods due to the fact that I grew up a little too far away from it, where I got used to different rules and railway operation procedures, I dare bringing some of these questions forward in a series of posts. I think that your answers might also be of interest to others, be it that they too are not familiar with North American RR, be it that they are new to the rails per se. The other topics are to be found in the following posts, which I decided to split in the sake of keeping each subject focused:Questions regarding Multiple Unit (MU) running of prototypical locomotives at http://www.train-sim.com/dcforum/DCForumID1/5339.html
Questions regarding geographical assignment of prototypical locomotives at http://www.train-sim.com/dcforum/DCForumID1/5338.html
Quesitons regarding realistic scheduling of my AI trains on US routes at http://www.train-sim.com/dcforum/DCForumID1/5340.htmlNow for my question regarding prototypical speed limit policies for various train types:Many users of MSTS have found out the hard way why the speed limit on some grades of the various US routes are quite low: With the long, heavy trains of 60, 80, or 100+ cars some of the railroads operate over these grades, these limits make nothing but a lot of sense.MSTS limits us to signposting two sets of permanent speed limits at the max on any given stretch of track: A speed limit for (pure) passenger trains and a speed limit for trains containing any freight wagon. This made me wonder if this is prototypically correct, namely the part that the same speed limit applies to any freight train regardless of its weight and power. Excuse my ignorant asking, it may very well be true that most or all RRs went the easy way in posting one universal speed limit for all freight trains, but I could at least imagine that some RRs also went the more pragmatic approach of publishing a variable speed limit which is calculated – and published in the engineers manual – based on a table of total weight of the train, power available, and types of cars used. The last of these factors is the most easy one to explain: A train can never go faster than the maximum speed allowed for the slowest car in the consist. And believe me, there must be some types of cars which will be certified for a maximum speed that is lower than the maximum speed signposted on a route: Schnabel cars come to my mind, due to their excess weight, or cars carrying hazardous materials such as explosives, as well as cars with technical defects that have to be dragged along carefully to the next siding. What other types of cars or situations do exist that limit a train’s speed permanently under US RR laws, and what would be the protoypically correct figures?Regarding the weight and power issue. When driving down those wide sweeping curves on BNSF over Cajon pass into San Bernardino with a short local freight consisting of an SD70, five boxcars, a logger and three grain hoppers, the virtual engineer may ask himself / herself whether it is prototypically correct or not that in MSTS his light, ample powered train is subject to the same 30 mph limit as 3 Dash 9’s with 80+ loaded Bethgons going down the hill? Do some or all of the big RR’s differentiate maximum speeds of freight trains depending on their load, or is the signposted speed at the same time the speed good for any freight train, including the heaviest, most dangerous one, to which speed also the lightest freight train must adhere simply due to the fact that it, too, is a freight train?Hope I got my point across. Now looking forward to some answers, thanks in advance.Lukas a.k.a Swissie
(Edited for the links to other threads posted parallely)

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Ok, here's the shortest and simplest answer:Factors accounting for speed limits are: old/bad track, repair crews working in the area, new track or newly repaired track, track that has sharp (for standard guage anyway) curves or grades, among other factors.For example, when you're driving on the highways you'll come to curves that have the maximum safe speed limit...say 45 mph...that the highway department has deemed the highest speed you can safely take the curve without risk of overtaking the other lane, flipping your car, etc. Basically the same thing on a RR, but a train can't simply slow down when they see the sign 50 yards before the curve. Therefor that entire section of track would be a slower speed limit.Same thing with grades...there's a certain speed at which it would become unsafe to continue.Also, in summer time (at least down here) rail becomes very very hot and has a tendency to go out of guage in one way or another. This can mean bad news for a fast-moving train. Obviously a train is limited by it's lowest geared locomotive or slowest car (as you said)....but that doesn't really effect the speed limit for ALL trains. Also, just as an aside....freight trains are easier to manage than passenger trains (usually) because a freight train is normally much longer than a passenger train, allowing most of the in-train forces to equalize. One half of the train might be going uphill, but the other half is going downhill.....see what I mean?Blake Harris
Engineer/fireman, Jefferson and Cypress Bayou Railroad

Vice Dean, Limbaugh Institute for Advanced Conservative Studies

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