I took the step and started testing what US locomotives DO work in free roam mode on TSW 4 here are a few i tested so far with success 1 UP SD40 2 ..2 UP and NS GP38 2 .. 3 MP36 F40ph 2 Cat ..will test more soon to see what works.these tests were done on X Box S and horseshoe curve on south fork branch .. Note for fun i tested a EWS class 66 buckeye coupler to UP box cars and it worked ...there is some hope for the US routes at least there are some Us locos that work ...go hook up a trio of UP SD40 2 s or creators club livery ones and Have FUN..
side note to use those locos you have to have the DLC ie sherman hill peninsula corridor horse shoe curve
Not all locos can be placed on all maps because some routes use different track gauges. For instance, you can't place a lot of common locos on Clinchfield RR because the tracks are narrow-gauge.
Hmm, fair enough - I could have sworn it was narrow-gauge, but it appears I misremembered it. With that said, though, I also can't find any engines the game isn't letting me place, so it leads me to wonder a little bit whether something else is wrong. This is even holding true on tracks that definitely ARE narrow-gauge.