I recall seeing within the last two decades an write-up in the British The Railway Magazine showing brush painting of modern, mainline, railway equipment. The reason being to avoid the need for respirators and spray booths.

[PS The Railway Magazine just celebrated 125 years of publishing to the rail enthusiast community.]

Purely speculation here and I'll play the devil's advocate:

I don't have direct evidence for the overall railroad industry but I would argue that anyone that adopted nitrocellulose lacquers and alkyd enamels in the '30s or later would have made spray painting almost mandatory. Both of those paints, mainly the lacquer, were used primarily because of the quick drying time (enamel just a little slower than the lacquer) which doesn't lend itself to brushing a large surface without leaving overly obvious overlap marks from dragging your brush or roller through tacky paint. Though I'd guess you could have two guys doing a spray and roll/brush if you worked quickly but why would you? The quick drying meant that you could paint a lot more cars and have them dry in in a matter of hours. Time is money and if you had a large fleet to maintain, I'd assume you'd spray. But then, railroads did weird stuff.

Both Binks and DeVilbiss atomizing compressed air spray guns gained widespread use in the '30s. With DuPont's early early stake in GM and close association after divestiture, you can bet EMC/EMD locos were sprayed. I'd also think that the rail car manufacturers would have been early adopters.

Small fleets with more equipment downtime to paint would probably stick with something brushable since that's what they knew ("Change bad" say Frankie). The older, slow drying varnishes, shellacs and linseed oil/japans could be worked for much longer times and still achieve a smooth, blemish-free finish using only brushes though they took a week or more to dry.

More evidence would be in how the paint weathered. Brush marks would be more obvious as the paint weathered off.

I guess what it comes down to is if the particular railroad invested into spray equipment verses labor early on or not. To each railroad its own.

My preference has been for brush and roller painting since much of what I have done was done out in public where overspray and environmental considerations prevailed. I also agree with the idea that brushing works paint into places sprays can't in normal application since it would generate runs. I use spraying for things like undercarriages where masking off below the side of the car with plastic is easy and the results underneath aren't very visible and therefore are very forgiving. PPG had a water based industrial enamel that was very environmentally innocuous relative to automotive paints which worked well for the purpose, maybe they still do. I also prefer to have display equipment reflect the average on-the-road-in-service appearance rather than something newly out of the paint shop as a more accurate representation of history.

True, but that wasn't the issue raised in discussions in the trade press of the day. Those arguments postulated that ALL substrates are porous (wood certainly is, but the claim was made that iron and steel also have microscopic pores) and that brushing was better at forcing the paint into those pores, eliminating potential corrosion and improving mechanical bond. I have seen specifications for structural steel from the same era that stated that spray application of paint was allowable, so long as the paint was subsequently worked with a brush.

I make no judgement of the validity of this argument, only pointing out it was a concern at that time.

I can attest to the "porousness" of materials. The heat from welding or brazing on old metal that's been in a greasy or oily environment will make oil magically pour out of all the unseen microscopic nooks and crannies- even with vigorous degreasing and cleaning beforehand. It just soaks in and will never all come out. Whether or not paint works itself into those same surface imperfections I don't know, but at least in theory I can understand the reasoning.

I am curious though to hear of everyone's experience in the longevity of paint jobs that are brushed/rolled vs sprayed. In my mind brushing will result in a thicker coat than even a couple passes with the spray gun- does that effect the long-term durability of the paint job?

Not if you spray painted like I did :-) Especially the job where I foolishly decided that oxide red primer was close enough to bright red to not need an intermediate coat of light color primer :-(

Thickness of the color coat only determines how long it will weather before it's totally gone... but long before that other problems will develop; rust will bleed out of lap seams and streak down the sides, rust will start at stone chips, and the worst one, if the surface wasn't taken to bare metal, the previous coat(s) of paint will let go and start peeling off.

Anyway, the thing that kills the appearance is oxidation of the surface, and the most effective way to fight that is the hard finish provided by automotive products, or the marine epoxy products, some of which are brushable.

Case in point is Illinois Terminal 415 at IRM. When initially repainted in '73 or '74, the light green was done with Dulux, but someone insisted that the proper cream was available in the PPG industrial coating line. That was a mistake, within three or four years the cream was dead flat and lifeless, while the green was still glossy, but streaked with rust from a poorly sealed belt rail. I re-caulked the belt rail (thankfully there was a black separation stripe that made this possible) worked the rust off with auto polishing compound, shot a clear coat over the whole car, and it looked decent again. I see it's now being repainted again, but it lasted forty years.