Linney Street is a public street, not solely for the post office, based on what I can tell from its signage. There isn't any sort of 'no thru traffic' sign at its beginning and with the Bing street imagery the iD editor provides, I think I can make out an 'adopt a highway' sign (which I don't believe would be posted along a private service driveway) and some kind of red-on-white text sign that's most likely a private parking sign. However, Bing's street view imagery is horrible and I could be wrong.