FYi, BNSF Cherokee Yard in Tulsa runs (2) SD70MAC pairs for Hump operations.

Can’t use GE’s, that’s for sure...

Gee, why not GE's?

Interesting, AC traction for humping

Actually, it makes good sense.

• These locomotives have low-speed control built right into the design, not add-ons as are used on conventional locomotives commonly used in hump service.  SD70MACs were designed to operate at a constant low speed for flood loading of coal trains at the mine tipple, and for dumping at the delivery pit.  They compensate for the train weight increasing or decreasing, and continue to maintain constant speed.  This is ideal for humping.
• Two SD70MACs are powerful enough to hump a complete train, without having to reduce it to two or more cuts.
• Many -- if not all -- of the SD70MACs are fully-amortized.
• Coal traffic is down and unlikely to return to former levels;  these locomotives are available.  Utilizing them in hump service is far preferable to storing them.  Storing less efficient locomotives, and keeping the MACs working makes good financial sense.

These are "one-owner" locomotives, well-suited for hump service and for other service.

Thanks for the excellent explanation Number90.  That's why a love the real train forum, you, HW, and others who worked the real thing do a great job explaining operations and the how's/why's to the rest of us.

Yes, thanks for that info, Number 90 

As "NUMBER 90", i.e. Tom indicated above, all the EMD SD70MAC units were delivered with Speed Control. All the Engineer has to do is select "Speed Control" on his desk-top computer and then use the small rocker switch on the desk-top to increase or decrease the desired speed, in 10ths of a mile an hour, and the unit/units do the rest. I've been on many Powder River Coal Basin coal trains while being loaded, usually at 0.4 to 0.6 MPH, as the 125 to 135 bathtub gons are flood-loaded, and the tonnage simply keeps increasing. The "Speed Control" takes care of everything, even increasing engine RPM in order to maintain steady and smooth power.

Here is a shot of CSX70MAC 4553 made Nov 3 2019, eastbound on Q316, a daily manifest at Keyser WVa

This locomotive was one of the "heritage" MACs, and had the RF&P logo on the cab, but it and her fellow MAC, also in the loco consist here, which had the B&O logo applied, both were no longer on them this day.

Click on the photo for full size image.

Ed

This pair, 4553 and 4551 have been working on the "west end" for a time. Perhaps when they are not pulling a manifest, they too could be "flood loading" somewhere on the coal rich west end sub.

Ed