Silicon Valley's job boom has underscored gaps in the transit systems in the San Francisco Bay Area, and has renewed calls to extend BART, the costly regional transit system that was once supposed to ring San Francisco Bay. But while construction continues on a $1.5 billion extension of BART from northern San Mateo County to San Francisco International Airport, other plans to extend BART have received mixed receptions. A ballot initiative to extend BART south of the airport through San Mateo County surfaced and then was quickly pulled by supporters. And San Jose Mayor Ron Gonzales has recently said that he'd like to extend BART on the other side of the bay from Alameda County to his city. But funding for the estimated $3 billion extension is uncertain. BART currently runs from northern San Mateo County, through San Francisco and into Alameda and Contra Costa Counties. The extension to the airport is to be completed in December 2001, adding four new stations and bringing it 8.7 miles farther south into San Mateo County. The airport extension will include a connection in Millbrae with Caltrain, a train service that extends along the San Francisco Peninsula from San Francisco to Gilroy. Caltrain supporters, who have pushed to see their train system electrified at a cost of $376 million, are often critical of the billions spent on BART. The San Mateo County BART extension proposed for the March 2000 ballot would have run down the middle of Highway 101, a heavily congested north-south artery. Many of the Caltrain stations are already located a few blocks from Highway 101 in the same area, and they are being rebuilt and expanded. The San Mateo County proposal would have raised the sales tax by a half-cent. To extend BART 15 miles south from Millbrae to Menlo Park was estimated to cost between $1.5 billion and $2.5 billion. The measure was pulled after several members of BART's board of directors announced their opposition. A recent report by the Silicon Valley Manufacturing Group said that Silicon Valley already has worse freeway congestion than New York City when measured in time spent waiting in traffic. Plus, five million square feet of new office space is expected to be built in the region during the next five years, bringing about 15,000 more cars to already congested freeways and roads. But BART is not the only option for Bay Area commuters as traffic in the booming San Jose area has worsened. Other systems include: o Caltrain, which travels up and down the San Francisco Peninsula. o Light rail in Santa Clara County, which connects with Caltrain in San Jose. The light rail system will also connect with Caltrain in Mountain View when a new 7.1 mile leg of the system opens in December. The new leg, which brings the total light rail system to 28 miles, was built at a cost of $327 million. o Altamont Commuter Express trains, which run between Stockton and San Jose. This service has proven popular in its first year of operation. o Amtrak, which runs trains between Oakland and San Jose three times a day and has plans to increase its operation. o A new $90 million rail service approved by South Bay voters to run between San Jose and Union City's BART station in Alameda County. That service should begin within two or three years. BART, which started carrying passengers in 1972, has spent considerable money during the 1990s to upgrade its aging cars and stations, as well for seismic retrofits. Service has been extended to outlying regions in Contra Costa and Alameda County as well. The system currently has 95 miles of track and carries an average of 299,000 daily riders, accounting for about 8% or 9% of all Bay Area commuters. BART officials have also had a difficult time securing all the money for its expansion to the airport. The state legislature's failure to place a transportation bond on the next state ballot also hurt efforts to expand the system further. But many political observers expect transportation funding to be a top issue when the legislature reconvenes in January. BART was originally conceived as a regional transit system in the 1950s. But San Mateo County supervisors voted 3-2 against joining the system in the 1960s, and Marin County also dropped out. San Mateo County later changed its tune and had to spend $200 million to buy its way into BART when it joined in the 1980s. Buy-in costs for Santa Clara County have not been determined, but figures between $500 million and $1 billion have been suggested. "BART is the best Bay Area wide system right now," San Mateo County Supervisor Mike Nevin said. Nevin said that Caltrain's daily ridership of 27,000 riders a day is smaller than the total number of daily users at BART's Daly City station. If BART extends south, he said, "you can't afford not to use it." The BART airport connection will have departures every 15 minutes during peak hours. BART rides to downtown San Francisco will take about 30 minutes. (A people mover will carry passengers once they are at the airport.) The airport extension is expected to eliminate 10,000 car trips per day and boost BART ridership by 70,000 passengers a day. The airport connection is expensive, and project costs continue to grow. Originally, the extension was estimated to cost $1.1 billion; now the cost has jumped to $1.483 billion. The federal government pledged to pay $750 million of that cost in 1997, but Nevin said "they've shorted us several million dollars over the past several years." He blamed the lowered appropriations on a Republican Congress. "It's still a crisis in Washington to get the funding," he said. Funding for the airport extension comes from a variety of sources besides the feds: $26.5 million from the Metropolitan Transportation Commission, $171 million from Samtrans (San Mateo County's transit agency), $152 million from the state, $200 million from the airport, $143.7 million from BART itself, and $40 million in bond money. The BART airport connection will not be the first in the U.S. for a rapid transit system. Washington, D.C.'s Metro system takes passengers to Reagan National Airport while Chicago's trains carry passengers into O'Hare International Airport. BART spokesman Mike Healy said that even though BART tracks are not much more expensive than light rail lines, right-of-way acquisition costs and subways construction escalates the total cost of BART projects. The airport extension is almost entirely a subway because local communities demanded it, he said. Contacts: Supervisor Mike Nevin, (650) 363-4653. BART Spokesman Mike Healy, (510) 464-6000. Peninsula Rail 2000, a Caltrain support group,