former CNW SD40-2s nearing their end on UP? - Trains Magazine

Per the A-A-A, excellent question!

The answer can be found at Don Strack's excellent CNW site:

UNIT WEIGHT CLASSIFICATION

C&NW classifies its units by weight, with the class displayed on the locomotive cab side:C&NW
Weight
Class Pounds Per Axle Pounds Per 4-axle Per 6-axle Locomotive
Locomotive

C 0 to 49,999 0 to 199,999 0 to 299,999
B 50,000 to 54,999 200,000 to 219,999 300,000 to 329,000
A 55,000 to 61,499 220,000 to 245,999 330,000 to 368,999
A-A 61,500 to 64,499 246,000 to 257,999 369,000 to 386,999
A-A-A over 64,500 over 258.000 over 387,000