Trends toward Self-Containment in the Bay Area
Ratios of jobs to employed residents indicate only the potential for balance. The degree to which that potential is realized is reflected by the share of the jobs in a community that are actually filled by residents, and conversely by the share of workers finding a place to live in that community-or what has been called "self-containment" (Cervero 1989). Self-containment refers to achieving a built form that allows people to live, work, shop, and recreate within a community (Burby and Weiss 1976). In a study of British new towns, Thomas (1969) first devised a measure of self-containment. According to Thomas (1969,338), all British new towns were designed to be "self-contained and balanced." For tracking changes in self-containment from 1951 to 1966, Thomas created an "Independence Index" -- the number of internal (within community) work trips divided by the sum of in and out (external) work trips. The higher the value, the more "independent," or self-contained, the community. Thomas found that early (Mark I) British new towns became more self-contained over the course of the 1960s. More recently, Breheny (1990) has shown that self-containment within British new towns has declined, though the newest generation of British new towns have maintained high levels of self-containment (Cervero 1995).
Table 2 presents 1980-1990 changes in Independence Indexes computed for the 23 Bay Area cities, along with two other measures: the percentage of locally residing workers and the percentage of locally working residents. The percentage of locally residing workers refers to the share of workers who reside in the same city where they work. The percentage of locally working residents refers to the share of employed residents who work in their home city. High values for both percentages signify self-containment. (Cities are ordered in table 2 as in table 1-according to J/ER ratios.)
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