About  east of the western terminus, SR 312 passes over the Florida East Coast Railway main line via an overpass. from the western terminus, SR 312 intersects U.S. Route 1 (US 1), with SR 312 continuing a few blocks east through St. Augustine until the Mickler-O'Connell Bridge over the Intracoastal Waterway.
SR 312 travels eastward from its western terminus, crossing the Florida East Coast Railway main line via an overpass. It then intersects US 1 before continuing east through St. Augustine to the Mickler-O'Connell Bridge over the Intracoastal Waterway.