This tends to be a reoccuring hotly debated topic not the least because the legal situation as escada writes tends to be different from country to country.
If bicycles are a simply allowed on a way that normally would be closed to them:
bicycle=yes
just the same if pedestrians would normally not be allowed to use a way
foot=yes
While some what disputed: *=designated IMHO indicates that the way in question is at least intended for the mode of transport (in many countries not just intended it may be legally mandatory). mandatory and may exclude other means of transport). So a dual purpose cycleway or footway can be tagged either as:
highway=cycleway
foot=designated
or (with the same implications from a pratical point of view, but different renderings on the default map style)
highway=footway
bicycle=designated
Please add a segregated=no or yes if there is some kind of clear division between the areas on the way that are used for the mode of transport. Further if the way is clearly a sidewalk, a footway=sidewalk would be helpful.
Note: mainly in Germany the value "official" is used to indicate a way that is mandatory to use for the mode of transport. It however tries to model a distinction between mandatory and non-mandatory use that IMHO doesn't really legally exist in Germany.
