sentences:  Prolonged disruption to what had traditionally been the social and economic center of the city contributed to the decline of the mid-Market shopping district in later years.On June 4, 1968, voters in San Francisco approved Proposition A, which issued $24.5 million in bonds to pay for the reconstruction and improvement of Market Street to follow the completion of the double-decked subway.In 1980, Muni's surface operations were partially routed underground with full service changes occurring in 1982.