SUB-CENTRING AND COMMUTING - EVIDENCE FROM THE SAN-FRANCISCO BAY AREA, 1980-90

Like many large US metropolitan areas, the San Francisco Bay Area has experienced rapid suburban employment growth since 1980, much of it co ncentrated in sub-centres. This paper shows that, contrary to the co-l ocation hypothesis, employment decentralisation has not been associate d with shorter average commute distances or durations in the Bay Area. Combining statistics on shifts in modal splits and average vehicle oc cupancy levels reveals that parallelling the region's sub-centring tre nd has been a substantial increase in average commute vehicle miles tr avelled (VMT) per employee between 1980 and 1990. The largest increase s occurred in the fastest-growing and most remote suburban centres, Us ing decomposition analysis, we found that increasing commute distances contributed the most to rising commute VMT per employee, and the dist ance factor had proportionately the greatest effect on rising commute VMT rates in the most peripheral work centres, Since shifts in commute VMT per employee are thought to be strongly associated with transport externalities, we conclude that the social and environmental implicat ions of the Bay Area's regional growth trends deserve more public poli cy attention than given to date.