As the new Open Street Map API 0.5/0.6 supports turn based restrictions in JOSM, this blog will show how to add these restrictions to the OSM database.
A turn based restriction is made up of two nodes/ways a, to value, from value and via node. Basically you will need to select which is the node/way with the restriction starts (the from value), the node/way where the restriction ends (to value) and the node/way where you could normally cross at (via).
Open JOSM and click on the relations button at the bottom of the side bar (highlighted in green) and the relations bar appears in the bottom right pane (blue).
To create a new restriction (which is a relation) click new (Orange) where you will be presented with the screen below,
From here add the tag ‘restriction’ (orange) with the value of that restriction say a ‘no_left_turn’ or ‘no_right_turn’ (for a full list see here: http://wiki.openstreetmap.org/index.php/Relation:restriction )
Then add the members (yellow) to the relation ie. the to, from and via segments. Click on the way/node where you want to add the member then enter, do this for all the ways and their assoiciated restrictions then click OK and then upload it to OSM.
Here is the web page of the relation that I uploaded from JOSM as part of this example… (The webpage is here: http://openstreetmap.org/browse/relation/22104)