In the 1960s there was increasing agitation in Panama to achieve greater Panamanian control over the canal, resulting in the negotiation of a new treaty (1967) which failed, however, to gain ratification by the Panamanian government. In 1977 negotiations were successful, and a new treaty was signed. It returned the Panama Canal Zone to Panama while setting up joint U.S.-Panamanian control of the canal until the end of 1999, when Panama gained full control. A separate treaty (1979) guarantees the permanent neutrality of the canal. In 0ct., 2006, Panamanian voters approved expanding the canal by adding a third series of locks paralleling the existing locks; the new locks, whose construction was inaugurated in 2007, will be larger, enabling wider, longer vessels with deeper drafts to transit the Isthmus. The plan will utilize the work begun but abandoned on a third series of locks prior to World War II.