Old 02-25-2009, 08:10 PM   #1
dejv
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Default Loads per axle/length

What are permitted loads per axle or length of train on U.S. railroads?
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Old 02-25-2009, 08:49 PM   #2
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I'll be interested to here the tech/rule junkies pop in on this one.

My understanding is that for most/all US mainlines there is a limit of 286,000 pounds total weight, car and load ("gross rail load"). This would be spread across 4 axles / 8 wheels.

The previous limit was 263,000 pounds and there are still secondary lines and branch lines that have not been upgraded to accept heavier cars.

Oddly, this does not seem to be based on an axle or wheel limit but rather a car limit. Perhaps there is something in the more technical rules area that creates standards per axle/wheel, from which the 286,000 comes out if one calculates based on 4/8, but I don't know. I don't know what limits are imposed on the (small minority of) cars that have more than 4 axles.
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Old 02-25-2009, 09:46 PM   #3
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Thanks Janusz, that's essentially what I thought. In metric system it means 32 or 30 t/axle. The weight per wagon rule is quite weird indeed, because train weight per length is the most important input for bridge design calcuations...
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Old 02-25-2009, 10:18 PM   #4
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Maximum train length varies by line and railroad, as does maximum tonnages. Where I live, the maximum train length is 14,000' and the maximum tonnage is 12,000 tons, for an intermodal train at least - when they reach either of those points, the crew can refuse the train. A supervisor can order the crew to depart anyway, but then it's on their shoulders if something happens - most of the time they'll opt to cut off the excess length instead.

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Old 03-02-2009, 06:52 PM   #5
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263,000 gross with MOST car structures riding on 6"x11" and 5.5"x10" bearings. 286K gross with MOST cars riding on 6.5"x12" bearings. The only trailing restrictions that I am aware of is in regard to cold weather length restrictions and powered axle per ton restrictions. AAR in Pueblo, CO has tested 315K gross on 6.5"x12" bearings on 286K cars and kept breaking axles during the tests. Weight limits on branches and other tracks depend on the track conditions and bridge restrictions. Some carriers even prohibit the use of 6 axle power on certain tracks.

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Old 03-02-2009, 07:36 PM   #6
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Quote:
Originally Posted by dejv View Post
Thanks Janusz, that's essentially what I thought. In metric system it means 32 or 30 t/axle. The weight per wagon rule is quite weird indeed, because train weight per length is the most important input for bridge design calcuations...
If a carbody is designed to hold a certain amount of weight, how is that weird?

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Old 03-03-2009, 08:31 PM   #7
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It's weird from my European POV, because here isn't (or historically wasn't) the weakest link frame of the car, but bearing capacity of track and subgrade. See load map of Czech network (map 7 here) and compare it to values of UPRR (which I couldn't find before I got replies to this thread ). UP's values converted to metric tons per axle and lengths (the same as in czech map) are these
red: 30,39/ -
blue: 32,43/8,74 metric tons per axle/meter
red: 35,72/8,84

UIC also knows higher loading classes ending at 30/10 tons per axle/meter, but they aren't used here.

There are more things connected to this topic that one can find weird when viewing from point of view on the other side of the ocean. Like high axle load on ancient-style fastened rails in America or presence of many two-axled freight cars in Europe.
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Old 03-04-2009, 01:18 AM   #8
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Ok, whatever your POV is, the facts in the USA are simple. We railroads err on the side of safety, a carbody is only tested to 286K. It is a known fact that exceeding this load with current US axle usage ( not actual carbody capacity ) and design will result in axle failure. I speak fact, so your "weird" idea is based on your possible ideas, my facts are backed with hard data that I would be VERY happy to provide. You asked a question regarding trailing ton restrictions and car capacities in the USA. Where are you going with this?
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Old 03-04-2009, 07:46 AM   #9
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I'm a civil engineering student trying to get broader views. I actually asked because I wanted to compare load on bridges on both sides of ocean. Thanks to UP's map I could answer myself - concentrated loads are up to 45 % higher and distributed up to 10 % higher.

Quote:
Some carriers even prohibit the use of 6 axle power on certain tracks.
Due to vertical or lateral forces?
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Old 03-04-2009, 01:26 PM   #10
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Quote:
Originally Posted by TheRoadForeman View Post
Ok, whatever your POV is, the facts in the USA are simple. We railroads err on the side of safety, a carbody is only tested to 286K. It is a known fact that exceeding this load with current US axle usage ( not actual carbody capacity ) and design will result in axle failure. I speak fact, so your "weird" idea is based on your possible ideas, my facts are backed with hard data that I would be VERY happy to provide. You asked a question regarding trailing ton restrictions and car capacities in the USA. Where are you going with this?
A bit of grouchy response, no? I think there is a legitimate question here, one you might help in explaining if you change your mood.

In trucking, for example, loads are limited at the axles as well as overall for a truck. So you not only can't overload a truck, you have to distribute the load properly over the axles. Why in the US rails is there only a carload restriction and not a truck/axle restriction? Is there a presumption that RR cars tend to be evenly loaded front/back? Obviously that will be true of some of the heavy loads, like coal/ore. But what about tank cars with multiple compartments? Is there a regulation ensuring those are evenly loaded front/back, or in practice do tank cars generally move fully loaded? A clarification would be nice, please.
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Old 03-04-2009, 08:05 PM   #11
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Quote:
Originally Posted by dejv View Post
I'm a civil engineering student trying to get broader views. I actually asked because I wanted to compare load on bridges on both sides of ocean. Thanks to UP's map I could answer myself - concentrated loads are up to 45 % higher and distributed up to 10 % higher.


Due to vertical or lateral forces?
Deteriorated tie conditions and excess curvature is the most common reason.
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Old 03-04-2009, 08:21 PM   #12
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A bit of grouchy response, no? I think there is a legitimate question here, one you might help in explaining if you change your mood.

In trucking, for example, loads are limited at the axles as well as overall for a truck. So you not only can't overload a truck, you have to distribute the load properly over the axles. Why in the US rails is there only a carload restriction and not a truck/axle restriction? Is there a presumption that RR cars tend to be evenly loaded front/back? Obviously that will be true of some of the heavy loads, like coal/ore. But what about tank cars with multiple compartments? Is there a regulation ensuring those are evenly loaded front/back, or in practice do tank cars generally move fully loaded? A clarification would be nice, please.
Grouchy? No. Tired, yes! Tank cars only have one compartment these days and they are not baffled either. The lading must be evenly distributed over the entire car prior to shipment per AAR loading rules, also, if a covered hopper only has the hopper fully loaded at either end, while the other hoppers are empty, it cannot be moved until the product is either removed or, evenly distributed into the other hoppers within the car. If a car is grossly overloaded, the springs on the trucks will compress to their limits and the truck sides can touch the car sill and possibly prevent the truck from turning in a curve. I also have seen an overloaded car that compressed the springs so badly, that the wheel flange actually came in contact with the floor of the car. Here is another thing to keep in mind regarding allowed tonnage, if a tractor-trailor is overloaded and damages a road surface, tax dollars are used to fix it. If a railcar is overloaded and an axle failure occurs that causes a major derailment, the bill goes directly to the carrier, not the government. I hope this gives a clearer understanding of our loading rules and why it is important to stay within the max gross weight.

Last edited by TheRoadForeman; 03-04-2009 at 11:33 PM. Reason: Noticed some ill-worded info.
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Old 03-07-2009, 01:07 PM   #13
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Quote:
Originally Posted by TheRoadForeman View Post
Grouchy? No. Tired, yes! Tank cars only have one compartment these days and they are not baffled either. The lading must be evenly distributed over the entire car prior to shipment per AAR loading rules, also, if a covered hopper only has the hopper fully loaded at either end, while the other hoppers are empty, it cannot be moved until the product is either removed or, evenly distributed into the other hoppers within the car. If a car is grossly overloaded, the springs on the trucks will compress to their limits and the truck sides can touch the car sill and possibly prevent the truck from turning in a curve. I also have seen an overloaded car that compressed the springs so badly, that the wheel flange actually came in contact with the floor of the car.

I do have a question about your statement about in a "covered hopper" having loads at either end should be evenly distributed. I totally understand the premise but in reality, since the hopper is "covered" and would gather to guess in open gondolas too, how is one really going to check to make sure all loads are uniform? The time factor alone would be crazy as it's not something you can just drive by and look at even though safety is involved.

It seems you are trusting the place of origin to load the cars properly unless countless hours are spent climbing up car ladders to check and I don't see much of that happening. Then again, you'd think a fully loaded hopper would make sense being shipped anyway. How often are covered hoppers partially filled?

Thanks for your anwers.. Rich
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Old 03-08-2009, 04:10 AM   #14
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[quote=bigiron;84766]I do have a question about your statement about in a "covered hopper" having loads at either end should be evenly distributed. I totally understand the premise but in reality, since the hopper is "covered" and would gather to guess in open gondolas too, how is one really going to check to make sure all loads are uniform? The time factor alone would be crazy as it's not something you can just drive by and look at even though safety is involved.

It seems you are trusting the place of origin to load the cars properly unless countless hours are spent climbing up car ladders to check and I don't see much of that happening. Then again, you'd think a fully loaded hopper would make sense being shipped anyway. How often are covered hoppers partially filled?

Thanks for your anwers.. Rich[/QUOT

Possibly, I could have worded that poorly. A single hopper cannot be full at either end while the balance of the car is empty. The conductor is responsible for making an inspection prior to departing the customers siding , plus, pound on the side of the car with your hand and you will know immediately if the car is loaded properly. The problem here can occur if the customer starts unloading the product and then decides to reject it for some reason or another, get the point? Otherwise, with a customer loading a car, it will be loaded to capacity, inspected and moved to it's destination.
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