I was looking at MapQuest's Nominatim service, and it seems like they have a non-standard search parameter (doesn't seem to exist in standard Nominatim's list of params) that is the routeWidth. Any guess how this is implemented in their service?
routewidth > Specify the buffer radius of a route. Acceptable values are between 0 and 1 (in degrees).
routeWidth is set here:
The parameter is part of the next release of Nominatim which you can find the source for here: http://svn.openstreetmap.org/applications/utils/nominatim/
The new version has not yet been released but will be in the next few weeks.