In this case, the street is canonically *both* Western Ave and River St. Neither is more "official" than the other; it is simply a road that has both names (until it splits), so alt_name is not suitable for either. I need to add name:left and name:right, but apart from that, this is the form used in two streets linked in the OSM wiki: https://wiki.openstreetmap.org/wiki/Key:name:left#Examples (cf. the ones in Cincinnati)