Some what like a Schnabel car, possibly.

However loads are specifically designed to be transported with a Schnabel car. The big transformers have a pinned joint at the lower corners of the transformer. These securely connect the load with the railroad car. The upper corners of the transformer are forced by gravity onto "stops" at the top corners of the railroad car. Gravity makes the three parts (load and 2 railroad cars) a solid unit.

To make this trailer work (without any load on the "temporary" middle axle) it will be necessary to make a rigid connection (at multiple locations) between the loco frame and the two trailer frames. That would best be done with multiple chains (or cables) around the frames of loco and trailer halves.

Not sure how to do that with out running chains through the engine compartment and cab. Or adding significant chain attachment points under the frame.

You can't just put blocking between the loco bolster and the trailer frame and install tie downs. The "middle" of the trailer frames will deflect downwards.

Perhaps I am misunderstanding their rig, or missing a detail.

Note that these connections between the trailer and the loco are very different than a standard "tie down". A tie down is meant to keep the load in place on the trailer, they are not structural connections and do not support the weight of the load. The connections necessary between this trailer and the loco are structural members and need appropriate engineering consideration.

Nothing against truckers, but as an engineer (the math and science kind) I think there is something missing in this design (or the explanation of how it will be used). I took my first course in "statics" (analyzing how loads get distributed in a structure, like a bridge) way back in the 1970's and this setup looks "hinky" to me.

Of course I wish them the best of luck.

Wikipedia says an Alco S4 is 46 ft long, so figure the bottom part of the trailer is a pair of 50 ft long beams. The articles quoted above said the locomotive's trucks are going to be moved separately, so I assume the loaded locomotive will be supported by its jacking pads. If the beams are directly under each jacking pad, then there are four point loads, two on each beam.

In statics terms, it is a 50 ft long beam with two point loadings on it, positioned so that both loadings are equidistant from the center of the beam. Statics tells us that when both of those point loadings are equal, then the shear at the center of beam is zero.... so the center connection of the trailer just has to be designed to withstand the bending moment.

I assume that when they're ready to move the locomotive, they will be able to place cribbing under its jacking pads, then use jacks atop the cribbing to lift it up enough so that its trucks can be rolled out. Then they can roll each half of the trailer under the locomotive (which would be another use for the center dolly.) The trailer would then be connected back together, without the dolly, and the locomotive lowered on to it.

That's what I assumed, is that the beam is just serving to keep the front and rear trucks in line. Personally, I would of made it so it would just chain/block/strap to the loco firmly and use the frame to align it, and then it would be easily variable length to accommodate other engines and even railcars. Reader RR has been moving their railcars like that for years, in fact they just have a frame to set one end of the railcar onto the towing truck, of course their cars are not as heavy as this one.

The Abilene & Smoky Valley RR posted this note today -

The trailer used to rescue the Staten Island ALCOs sounds similar. It was 4' wide, with two beams that were cross braced/connected. The trailer started out shorter and a section was built and added, with proper engineering, to make it accommodate the ALCOs. The couplers, steps, and air reservoirs were removed. The beam fit between the battery boxes with a few inches to spare on each side.

To load the trailer, three heavy duty tractor-trailer wreckers were used. The loco was lifted straight up, the trucks and reservoirs were rolled out, and the reservoirs were rolled out. They were previously lowered to a specially designed trolley that had mall flanged wheels and strapped down. Then the trailer was winched under the loco. The trailer also had a little trolley bolted to the end opposite the wheels which enabled it to be rolled under while staying in alignment. Then the tractor hooked the gooseneck up to the trailer, and the loco was lowered onto the beam.

Since the S2 was going to travel on I-87N in NYS, we had to get the height down, so the coupler pocket had to be removed from the cab end so that end would sit lower on the trailer. It was something like 14'5" once it was loaded. The height was the critical issue, not the weight, length or width. The S1 didn't have the same problem since it was going to a closer destination that allowed back roads without height restrictions, although the vent on the cab roof was smashed when it arrived so it barely cleared something.

Lessons learned? This can be done relatively cheaply if you are creative (wreckers instead of cranes, dolly design and construction, etc.). Using Union cranes was quoted to be $150 k and that didn't include the trucking so that was a non starter. Sending them back on the barge that the Brookvilles came in on was $600k, even though the cranes were there and the barge had to return empty anyway.

The trucker still has the trailer, so if anyone in the Northeast is interested in trucking an ALCO switcher please contact me. I don't think it would work on an RS3 or similar due to fuel tank location, or EMDs du to steps being cast and non-removable, at least with the O&W NW2 I was checking out while it was on it's trailer in Binghampton, which was more like a well.

YES We did get the S4 back to Abilene- We brought back the extras like air tank steps batteries boxes on one trip. Then we brought back the trucks on one load while we came up with a good way to move the rest.
The engineers that said the trailer would work in one way and we found out they were wrong.
We then turned the loco into the trailer with heavy I-beam on the ends.
We brought back the loco over about three days because of some problems that we expected and repaired on the spot. The trailer itself caused no problem. But if you ever moved anything that heavy your would understand that anything could go wrong. But we had NO major problem.
The loco and trailer is now at work area in Abilene.
We have no plans for the trailer right now.