The barriers of housing segregation have been reinforced for blacks living in central-city ghettos by the process of metropolitan decentralization, which has moved most whites beyond social contact, and most employment beyond reach of available public transportation. Despite gains in the number of blacks who found housing in the suburbs in the 1970s, the great majority of metropolitan blacks (71 percent) remain concentrated in the central cities of the largest Standard Metropolitan Statistical Areas, and their number is increasing as a proportion of the population. While whites have steadily migrated from the cities to the suburbs, blacks have steadily moved from the suburbs to the cities. Since World War II, employment, particularly blue collar employment, has left the central cities for suburban locations along regional highway networks. During the past 40 years, nearly two out of every three new jobs created have been in the suburbs of metropolitan areas, and most are not accessible by public transportation. These dramatic changes in the distribution of the population have profoundly altered patterns of access, and have produced increasing isolation among those without access to an automobile. In this group, blacks are greatly overrepresented. A list of 45 references is included. Extensive statistical data are included on 13 tables. (FMW)