The Air Quality Impacts of Urban Highway Capacity Expansion: Traffic Generation and Land Use Change

Since the mid-1970s, traffic congestion on California’s urban highways has increased markedly. The roughly 3 per cent annual growth in the ratio of vehicle-miles to lane-miles that occurred during the 1960s accelerated to 4 per cent from 1974 to 1985 and 5 per cent after 1985. Moreover, there was comparatively little upgrading of existing lane-miles over this period. As traffic density increased, so did congestion. By 1988, some estimates put the economic cost of congestion to California at $16 billion in time lost and $1 billion in fuel. Despite a California Division of Highways Plan, developed in 1958, calling for 12 thousand miles of limited access roadways, by 1990 less than 6 thousand had been completed.