Pieren
6
access=yes is implied everywhere. OSM is mostly mapping public access ways, so we use the tag access only when we have restrictions.
foot=yes is also implied for most of the highway classes:
http://wiki.openstreetmap.org/wiki/OSM_tags_for_routing/Access-Restrictions
In your case, you could use highway=service (+service=alley)+surface=unpaved or highway=track+tracktype=grade1 (where surface is implied, see the wiki)