Beyond wasting the truck and wasting energy (fuel) transporting the weight of the truck, the height of the truck and trailer on top of the train car would likely exceed bridge and tunnel heights.

1a. semi-skilled labor individually secures each and every truck to its flat car for safety. Figure 8+ hand-tightened heavy chains or freight straps per truck.

2a. if any mistakes were made during step 1a, then this train, flat car, and truck may enjoy 15 minutes of fame on the evening news.

2b. semi-skilled labor individually removes the heavy chains or freight straps from 1a, and stows them away.

America's railroads looked very seriously at doing this, back in the day. The economics really didn't work out. There is a sorta-similar concept that's still used - https://en.wikipedia.org/wiki/Roadrailer

That ties up the truck for several days while it's being shipped across the country, though. That's a very unproductive use of the truck. It's overall more efficient to do it the way you said the first time.

I know that. But it's a way to get started without needing expensive cranes and crane operators. It also works for intermediate low traffic dropoffs of freight. All you need is a platform level with the flatcar.

> All you need is a platform level with the flatcar.

Do you?

You can't drive a truck sideways (from the side of a parked train); you can't drive a truck across multiple rail platforms (from the end of a parked train); and you can't efficiently split up the train in individual cars, bring them to a rail-end where they can be driven to/from and reconnect them, that would be much more expensive in terms of machinery (locomotive) and operator use than a crane; train cars can be reshuffled but it adds significant time and effort compared to just lifting a container from a truck onto a train, which is how it's usually done. You would also need specialty (longer) flatcars to fit not only the length of the container but the truck as well.

There used to be TOFC (trailer on flat car) cars that had little flaps that you could lower so that you could drive between cars. They don't have those any more, for the most part. They found they could make them less heavy with a "spine" kind of design, which you can't drive across.

Also most intermodals these days use well cars which allow containers to be double stacked.

https://upload.wikimedia.org/wikipedia/commons/e/e5/DTTX_724...

> you can't drive a truck across multiple rail platforms (from the end of a parked train)

This is how we loaded our vehicles onto train when I was in the US Army. Everything from small vehicles to large trucks. There were removable pieces connecting the cars so they could be driven over.

Think of it like parallel parking. Not much room is needed, and the flatcar + the gap between cars can be longer than the truck by just enough to make it work.