Route 303 was a proposed state highway in the northeastern portion of New Jersey. The route originally was defined to go from an intersection with current-day Route 4 in Teaneck, then progressing northward through several local communities before connecting to the New York state line at Northvale. At the state line, Route 303 was to intertwine and become the current-day New York State Route 303 (NY 303). The alignment runs along the current alignment of County Route 505, which becomes NY 303 at the state line.