The Green Gate
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Transportation accounts for about 57 percent of the carbon dioxide (the primary pollutant responsible for global warming) produced in California. That figure far outpaces the national average of 32 percent for two reasons, one positive and one negative. The good news is that California's electric power plants are cleaner than those of other states, producing far less carbon dioxide. That means carbon dioxide emissions from the combustion of gasoline are a larger share of a smaller pie.

On the other hand, California's growing population is driving longer distances and spending more time in cars. The number of licensed drivers statewide increased 31 percent from 1980 to 1997, and population growth continues -- over the next 20 years, the Bay Area population is expected to increase by 14 percent. On top of this, the number of cars per household and the amount of driving per person have increased. What's more, traffic congestion wastes hundreds of millions of gallons of fuel -- in 1997 alone, some 280 million gallons, or approximately 91 gallons of excess fuel per driver.

Yet another factor is at play: decreasing fuel efficiency. This drop is a disturbing reversal of the longstanding trend toward greater efficiency, which resulted from federal legislation in the 1970s requiring auto companies to increase the average fuel efficiency of their vehicles. Although overall average fuel economy increased from 17.6 miles per gallon in the mid-1970s to 20.6 miles per gallon today, the popularity of sport-utility vehicles, which are held to less stringent fuel-efficiency standards, has driven down the average. As a result, average new-vehicle fuel economy is at the lowest point in 20 years.

All this travel and gasoline consumption comes at a high price, and not just at the pumps. While California has made great strides in cleaning up smog and soot, air pollution still threatens millions of state residents, about 90 percent of whom live in places, including the Bay Area, where the air is periodically unhealthy to breathe. Gasoline engines are primary sources of toxic air contaminants such as benzene and butadiene, which are known to cause cancer in humans, and respiratory irritants such as formaldehyde and acrolein. And carbon dioxide emissions from Bay Area vehicles also contribute to global climate change, which will have profound effects on our local climate and environmental health as well. Among the possible regional consequences: loss of coastal and bay wetlands, flooding in coastal areas, and salt-water intrusion that could threaten drinking water and agricultural land in the delta, the area where the Sacramento and San Joaquin rivers come together and flow into San Francisco Bay.

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