smz-osm
Actually lines 4.1 and 4.2, although they share some piers and they are roughly overlapping, are two very different lines: one (4.1) runs clockwise around Venice and the other (4.2) runs counter-clockwise. Same thing for line 5.1 and 5.2.

There are similar issues for many other boat lines, like the # and #2 that uses different piers in different directions.
Isn't there a solution for this?