The Alameda County Board of Supervisors voted Tuesday to approve an agreement to extend a lease agreement that will keep the Oakland Raiders at the Coliseum for at least one more year. The agreement also includes two additional one-year extensions that could keep the Raiders in Oakland for the 2017 and 2018 football seasons, as well. The board's action was considered a formality because a tentative agreement was announced by the Raiders and city of Oakland and Alameda County officials back on Feb. 11 and the Joint Powers Authority, which consists of city and county officials who oversee the Coliseum complex's operations, voted to approve the agreement on March 25. The agreement must also be approved by the Oakland City Council but the council is expected to vote in favor of it at its meeting Tuesday night. The agreement would then become final.