For the purposes of explanation, let A, B and E be regarded as initially
occupying zones X, Y and Z respectivly.

The six necessary "operations" are:
1. Draw B back into zone Z
2. Go round under the bridge and push A into zone Z, linking with B
3. Pull AB back, and then push up into to zone Y
4. Detach truck A from B and take A down into zone Z
5. Pass back under the bridge and push B into zone X
6. Finally, take A into zone Y and then return to zone Z for further duties.