it is a train for truck trailers transport,that uses the trailer as
wagons.
just like the french TGV hi-speed train ("mission impossible",do you
remember?) that has shared bogies between coaches.
But with trailers instead of coaches :-)
the green/grey parts on the train base are needed to avoid the trailer
to move sidewards.
You can use 1xn plates or 1x2 plates with door rail both on front and
back,as you prefer.
You can avoid to use them if you build the trailer base with standard
plates.
They stay perfectly fixed on turntables studs and the trailer won't
move.
Hope the pics are clear enough......
Comments are welcome.