Tonnage Ratinds and weather Reductions for locomotives

NW Mailing List nw-mailing-list at
Tue Dec 18 12:35:36 EST 2018

On 12/18/2018 9:47 AM, NW Mailing List wrote:

> Jimmy,
> I understand that. Your train length chart is from 1973 (dynamic-brake 
> diesel era).
> I’m trying to understand the possible reasons behind tonnage reduction 
> instructions shown in a 1953 steam era NW time table. I think the list 
> has figured out the reasons for diesel era train length reductions 
> well enough. All I’ve gotten so for cold weather tonnage reduction is 
> 1. Increased likelihood of broken knuckles 2. Increased rolling 
> resistance of friction bearings 3. And maybe decreased braking 
> capacity due to leakage. Are there other factors?
> John Garner

     I think it is all about the same thing, keeping the proper air 
pressure on the rear of the train. Note the portion below from a 1935 
ETT where it states that a train could be given over tonnage not to 
exceed car limit. Also note the very close resemblance between the two 
charts regarding temperatures and percentages.
In my experience, tonnage was not a concern. Not by the Yardmasters or 
the Chief Dispatchers. It was a case of..."Don't worry about the mule, 
just load the wagon!" And, we never had a reduction in tonnage just 
because of temperature. However, I do remember a time or two where they 
took cars off of us in Roanoke Terminal in order to get the proper air 
pressure on the rear. If you can't get the proper air pressure, you 
can't make a proper brake test. If you can't make a proper brake test, 
you are going anywhere!
     I will say one other thing about cold temperatures, rails will 
break before knuckles will!

Jimmy Lisle

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