Tonnage Rating of Locomotives

[nw-mailing-list at nwhs.org]

"But what numbers does the Tonnage rating refer?"

Chuck,
    Tonnage ratings refer to the maximum tonnage each engine is allowed to pull over each portion of track and still be able to maintain a minimum speed. 
    As grade increases the locomotives tonnage rating goes down. As the grade lessens, the more tonnage the loco can pull.

"I am guessing that 1) the Durham District's track, bridges, and other structures couldn't support the larger, heavier and more powerful locomotives"

    Tonnage ratings have nothing to do with the track, bridges, and other structures. The weight or more specifically, the axle loading, deals with what locomotives and cars can go on what track.
Jimmy Lisle
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