[mkgmap-dev] Routing over ferrys

Is there anything known about routing for cars over ferrys? I mean short ferrys routes over a river or over the Kiel-Channel like in my case. I tried several start an stop points that should cause the ferry to be the shortest and fastest way, but my garmin routes an other (much longer) way over the next bridge. The ferry is tagged with route=ferry, and I tried also with additional key motorcar=yes. Cheers, Jan