There has been a "significant" decline in traffic over the Bay Area's seven state-owned toll bridges, down about 2 percent over the first nine months of the current fiscal year, Metropolitan Transportation Commission spokesman John Goodwin said.
The figures have only so far been tallied through the end of March but are expected to remain consistent in coming months, according to Goodwin.
"What we see is a shift away from solo drivers to a big increase in carpooling," Goodwin said.
Carpooling on all seven bridges has increased 3.7 percent, up 5.2 percent on the Bay Bridge alone, Goodwin said.
Along with carpooling, public transit numbers have seen a big boost.
On the Golden Gate Bridge, which is not monitored by the commission, auto traffic decreased 1.2 percent in both March and April, with gas prices likely "a contributing factor," according to Bridge District spokeswoman Mary Currie. She said the Bridge District has recently seen an increase in bus passengers over the Golden Gate. Ferry ridership, though down recently because one boat was taken out of service for maintenance, has been steadily increasing since 2003, according to the Bridge District.
Bay Area Rapid Transit weekday ridership in May jumped by about 25,000 per day from last year, according to BART spokeswoman Luna Salaver.
"We could see that there's been a dramatic increase in 2008, and anecdotally, you could link that to the skyrocketing gas prices," Salaver said.
"And people are changing their habits because of the economy," she added, noting increases also in mass transit ridership for leisure and recreational purposes, such as taking BART to ballparks.
Salaver, also a spokeswoman for the Capitol Corridor heavy-rail train system -- which takes passengers between San Francisco, the East and South Bay areas, and Sacramento and Davis -- said the trains have already had 1.5 million riders in 2008, up from 1.3 million in all of 2007.
Ridership on both BART and Capitol Corridor trains is expected to keep increasing, and some BART riders are reporting it's becoming harder to find seats on BART during peak hours, according to Salaver.
"More people are looking to using public transit as an alternative to driving alone, and filling up their gas tanks," she explained.
Salaver said both agencies "would love to expand our service but we have to look at our budget and what's realistic at this time." Significant public transit cuts are expected at the state level this year, she said.
Alameda-Contra Costa Transit District has also reported significant upturns in bus passenger numbers between the East Bay and San Francisco, with more than 16 percent growth so far this year over the last.
San Francisco Municipal Railway carried nearly 5 percent more riders in the first part of this year than in the same period in 2007.
"For us, factors like the economy and the increased amount of service we have on the street are likely to be significant factors, as well as gas prices," said Muni spokesman Judson True.
The price of a gallon of gas hit an average of $4.60 in California on Tuesday, according to AAA spokesman Michael Geeser. Prices in San Francisco average $4.61, San Jose $4.58 and Oakland $4.57, he said.
Last year at this time, California gas prices averaged $3.24, according to Geeser.
"Gas prices are expected to remain up, at least through the July 4 holiday, and not expected to decrease any great amount until the end of summer," Geeser said.
According to Geeser, the spike in gas prices is linked to the rise in international crude oil prices, where the market is traded in U.S. dollars.
A nationwide economic slowdown, coupled with resultant cuts in federal interest rates, has lowered the value of the dollar, making oil more attractive for foreign investors, particularly in Europe, Geeser said. The increase in purchases of crude oil then pushes the price up, he said.
"We hope the value of the dollar will strengthen," said Geeser, forcing foreign investors to look elsewhere, and potentially driving the price of crude oil back down and relaxing gas prices, he said. "But that hasn't happened yet."
