Here’s an interesting variation: In the states the Wabash ran their 1st generation geeps short hood first and the New York Central long hood first.
However, for the fist gen GP units built in Canada and ran in Canada for the Wabash and NYC, they ran them exactly the opposite…!
(The Wabash ran between Windsor and Buffalo on the Canadian National and the NYC ran on their Michigan Central/Caso line.)
I shan’t, as some do, generalize from my own limited experience to the ‘same for any locomotive’, or ‘generally’ category. Here are my own observations, qualified as necessary:
Great Northern ran long-hood forward for safety reasons, as already mentioned here. I’m not sure they ‘ever’ changed this, but I could be corrected.
Quick research finds photos of Burlington Northern (green) engines with the ‘F’ on the long hood end of the frame, tending to support my guesswork in (1) above.
So there.
Careful with those generalizations. 
GN had SD-45’s that ran short hood first…
That would be correct for hi-nose first generation GPs. The confusion we seem to be having is that some railroads like GN bought their early GPs and SDs to run long-hood forward, and had a high short hood. In the early sixties they started buying engines with low short hoods and all of these were built to run short hood forward. Except for (as I noted earlier) a few NW and possibly Southern engines purchased in the eighties, all engines that were bought by any railroad with a low short hood were built with the short end designated as the front.
BN included railroads that ran hi-nose GP’s long hood forward and short hood forward, so it can be hard to tell what happened later. However, some long hood forward GN SD-9s lasted into the 1990’s if not later (I know they still have SD-9s, but not sure if they’re CB&Q engines or not) and I think some of them were changed to short hood forward at some point under BN, but I could be wrong. The ones I photographed at Northtown in the eighties had the F on the short hood as best I can recall.
While not GP locos, the Baldwins pictured below demonstrate principles applicable to EMD and other high-hood builders.
On the AS-616 unit, the orientation of the number boards, the paint scheme, and “F” on the frame end is the dead give-away this unit runs long-hood forward. For the ASB-616, only the “F” marking is the clue.
Mark
The Seminole Gulf Railway in Florida has owned 9 GP9s over the years, numbered 571-580. 571, 576, and 577 were built with the long hood as front. 572 was built with the short hood as front; 576 and 577 were built with steam generators and have torpedo tube air tanks on top of the long hood. All 4 units came from B&O.
Of course a diesel (except for an E or F unit where visability would be a problem) can go forwards or backwards equally well. That’s why railroads snapped up early diesels to use on branch lines, because they could do away with the turntable at the end of the branch for the steam engine to turn itself around…although a steam engine working backwards on a branch was more common than one might think!!
In any case, railroads rarely made an effort to turn GPs or SDs so yes an NW GP would often be working short-hood first - but it would be going backwards, since the long-hood was designated as the front.
You’re forgetting one step. For most railroads, their first diesel wasn’t an E or F unit, it was a switcher which was virtually always built to operate long hood forward. The first road-switchers, like the Alco RS-1 of 1941, was essentially an elongated switcher and was generally also used long-hood first, as were the later RS-2 and RS-3 engines.
On E and F units, you didn’t have an option which end was the front, so railroads all ran them the same.
The bottom line is that it’s impossible to make clear sense out of this issue as there does sometimes seem to be no clear rhyme or reason for what railroads chose to do. Great Northern ran both it’s GP-9 and RS-3 engines long hood forward, while next door neighbor Northern Pacific ran both engines short hood forward. But many railroads bought their early GPs to run short-end first but their RS-3’s to run long hood first. Plus starting around 1960 some railroads that bought early GPs to run long-hood forward switched to short-hood first when the low short hood was introduced, so you could have a GP-30 that ran short-hood first coupled to a GP-9 that considered the long-hood to be the front.
The law only requires the railroad to designate one end as “front”, it doesn’t require them to run that end forward. Diesels run just as well forward as backward. Crew comfort and possibly safety are another matter. When giving signals to a loco while switching the “Front” of the loco dictates whether you give a go forward or backup not the end the loco is on. Also when writing up defects on the loco the front has to be known for that loco to know which is the left side or right side and also which wheel you are talking about.
Richard lokking at MP 242 while working for the FEC Rwy.
PS Our GP7-9’s were set up short hood forward.