How do I add ferries

I would like to add ferry lines to the map, because they are part of the public transportation system. In my area they have also a function not just in transporting people and cars, but bicycles as well.

We have icons for airfield taxiing lanes (which I do not know how many people really need) but seem to have no category for ferry lines? Is this for any reason? So how should we do route-planning where ferries can have a major function to get to an island or to shortcut your route?