Bucksport and a private developer will begin extending two streets this summer as part of a plan to reduce traffic and create more commercial and residential development downtown. The extension of Park Street and Broadway is expected to add about 2,250 feet of new road to the downtown area, according to a project proposal by Woodard & Curran, an engineering firm with an office in Bangor, while lessening traffic on nearby streets, including Nicholson Avenue. The Planning Board approved the proposal with a 5-0 vote on May 7, Bucksport Code Enforcement Officer Jeff Hammond said. “The review went smoothly,” Hammond said Wednesday.