Kari Berglund isn’t a powerful political leader or transportation expert. She’s a 23-year-old Monte Sereno native working her first job in Chicago as a community health teacher.

But when federal transit officials gather at San Jose City Hall on Monday to sign over final papers to bring BART to the South Bay, she and young voters like her will have played a critical role in making it happen.

In interviews with numerous transportation experts, five key figures are credited with leading the successful effort to extend BART. Some are well-known: former Gov. Gray Davis, former San Jose Mayor Ron Gonzales and Carl Guardino, CEO of the Silicon Valley Leadership Group. Two others seldom have been in the limelight: Tom Blalock, a BART director from Fremont, and Carolyn Gonot, a planner with the Valley Transportation Authority.

But as important as their efforts were, voters — many of them college-age youths who cast a yes vote in 2008 that proved decisive in the second BART tax measure — were just as important. Without voters like Berglund, Monday’s celebration would at best be years away.

Here’s a look at these key players and a snapshot of their reasons for backing BART to San Jose, which will be the second-biggest public works project in the Bay Area after rebuilding the Bay Bridge.

The governor

Despite all the enthusiasm for BART in the 1990s, something was lacking — cash.

Davis changed that, approving $760 million in state funds for BART in 2000. This was the first time any money had been earmarked for the work, and despite the state’s budget difficulties over the past decade, every governor has kept the cash flowing.

“I’m pleased that a decision made more than 10 years ago has had such a positive impact on San Jose, which is ground zero as the most dynamic region in the state,” said Davis, now a senior fellow at the UCLA School of Public Affairs. “Silicon Valley moves at warp speed.

“We had to invest in those portions of our economy with the most upside potential, and clearly info-tech, biotech and cleantech have all done remarkably well. When government can chime in and help provide infrastructure, then you have a home run.”

The mayor

Gonzales began talking about a train link from the East Bay to San Jose as a county supervisor in the 1990s, when the dot-com boom brought freeway traffic to a halt. When he gave his mayoral state of the city speech in 1999, he talked about a rail link. He didn’t mention BART, but that is what many listeners thought he meant.

“That speech seemed to have lit a fire under everyone for BART,” he said recently.

With money pledged by Davis, a sense of urgency grew to come up with local funds. Gonzales turned to the board of supervisors to place a tax on the ballot that would need a simple majority. But he couldn’t get the votes to put a tax plan before voters.

Gonzales didn’t fold. He turned to the VTA, which as a special district needed a tax that had to win by a two-thirds vote. A Mercury News editorial compared it to a desperation half-court shot at the buzzer.

Swish.

Voters passed a 30-year half-cent sales tax, the first local tax measure for BART, by a 70.4 percent margin in 2000.

“It’s one of my proudest achievements,” said Gonzales, now president and CEO of the Hispanic Foundation of Silicon Valley.

The East Bay voice

Blalock, the BART director, knew that plans to extend trains from central Fremont to Warm Springs made little sense unless tracks continued into Santa Clara County.

“That just energized me to extend it to Santa Clara County,” he said.

Having a voice from the East Bay lifted this into a regional issue. Even if the South Bay had the money, nothing could happen without the BART board.

“He’s always talking about BART and the South Bay, to anyone who would listen,” Gonot said. “The fact that an East Bay guy was so supportive can’t be underestimated.”

The planner

Gonot, now the chief program officer for the BART extension, helped the extension overcome a near crisis: In 2004, the Federal Transit Administration gave BART to San Jose a “not-recommended” rating, which blocked the VTA’s goal of landing $900 million in federal funds.

The FTA dinged the plan because it lacked money to run the trains; the 2000 tax measure was for construction only. The federal agency also said the subway under downtown San Jose was too expensive.

Rather than battle, Gonot declared the FTA was right.

“It was so expensive to go all the way to San Jose,” she said. “And we needed money from somewhere to pay for operations.”

The VTA shortened the line to Berryessa and went back to voters a second time.

The money man

Say this about Guardino: The man knows how to run a tax campaign. He led successful measures in 1996 and again 2000, which will have raised more than $8 billion for transportation improvements in the valley.

He often logged more than 100 hours a week for three or four months. Workers could expect emails at 3 a.m.

The effort in 2008 to pass a one-eighth-cent sales tax to further fund BART seemed like skiing up the steepest Tahoe slope. Every poll said it would fail to get a two-thirds majority.

“Working 16-hour days almost every day and expecting similar commitments from others is difficult, when internally the people around you think all that emotional and physical investment is still going to lead to a defeat,” Guardino said.

Election night came, and it was too close to call. It would take four weeks before thousands of absentee and provisional ballots were counted.

Ever so slowly, the yes vote crept higher.

It won by 66.78 percent, just a hair over the 66.67 percent margin needed.

The voter

With Barack Obama on the 2008 ballot along with the BART tax, Proposition 8 and high-speed rail, young people seemed poised to turn out in numbers unlike most elections. BART backers flooded college campuses, where the mood for a second tax seemed upbeat.

Berglund, then 19, voted for the tax “because it would expand public transit options and make it less crucial to have a car to get around the Bay Area. An eighth-cent sales tax was reasonable given all the benefits it would bring.”

More than 600,000 votes were cast, and the measure won by about 2,250 votes. The FTA put BART on its recommended list and on Monday will sign papers clearing the way for $900 million in funds.

“I didn’t realize how close it would be,” said Berglund, adding: “I think that election really taught me how important every vote is.”

Said Davis: “Thank God for younger voters. They embrace the future more than the rest of us.”

Construction will begin in spring. Trains could be running by the end of 2016.

Contact Gary Richards at 408-920-5335.