You could try using a [roadAccess relation][1] although I'm not sure how many routing applications are aware of them.
them, as there [aren't many in use][2].
[1]: http://wiki.openstreetmap.org/wiki/Karlsruhe_Schema#Giving_hints_about_the_road-access_.28optional.29
[2]: http://www.openstreetmap.org/relation/270881http://taginfo.openstreetmap.org/relations/roadAccess
You could try using a [roadAccess relation][1] although I'm not sure how many routing applications are aware of them.
[1]: http://wiki.openstreetmap.org/wiki/Karlsruhe_Schema#Giving_hints_about_the_road-access_.28optional.29
[2]: http://www.openstreetmap.org/relation/270881