San Francisco Bay area households spend up to two-thirds of their income on transportation and housing costs, a severe burden that leaves workers with insufficient resources for other basic needs, according to a recently-released study.

The costs in the nine-county Bay area vary from 54 percent in Santa Clara to 66 percent in Sonoma County, the Urban Land Institute's Terwilliger Center for Workforce Housing said in the study released Wednesday.

The average household spends nearly 60 percent of their income on transportation and housing, the center said.

For one-fourth of all households in the Bay area, housing and transportation costs account for two-thirds or more of their income, leaving workers with insufficient resources for health care, education and food, according to the study.

The report blames "ever-sprawling" development resulting in a growing gap between where people work and where they live. The consequences are both economic and environmental _ transportation accounts for 40.6 of greenhouse emissions in the Bay Area, compared to 33 percent nationally, the study said.

Less than one in 10 Bay Area workers use public transportation to get to work, compared with 26.5 in the New York metropolitan area and 11.1 percent in the Washington, D.C., region.

The report, called "Bay Area Burden," includes an online cost calculator for individuals to gauge the combined costs of their housing and transportation decisions. It also allows them to explore how to lower their costs by moving closer to where they work or to where there is public transit.

The report was released to coincide with The Urban Land Institute's annual fall meeting, which began in San Francisco on Tuesday and is scheduled to end Friday. The nonprofit institute, established in 1936, examines land use in sustaining and creating communities worldwide.