Swap Coaches

[mjm11383]

This is a railroad laid in the form of a triangle. There is an extension upto 15ft on the left side and 10 ft on the right. The bottom rail is endless. The Engine (E) is 15ft long and the 2 coaches (A & B) are each of 10ft.
Now we need to bring coach A to the position of coach B and vice versa and the engine back to its original position.
See pic attached

[DeMan]

If I understand the question.......
E moves to the left and down Siding L Attaching A to the front and "pushing it down the bottom section.
E then moves up the Right Siding R (with A in tow optionaly) and attaches B to the other end, moving back down the Bottom Path, so YUou have in the bottom section:

B
E
A

E then pushes B up LHS and de-couples, returning to the centre section
E tows A up RHS, de couples and follows out throught the top.....

I assume, though, that I have somewhere violated the directions/corners that the train can make?