After a year of moving utility lines, knocking down old buildings and reconfiguring roads, the digging to extend BART to the South Bay is about to begin in earnest.

Work on the Santa Clara County portion of Silicon Valley's most expensive public works project ever has been underway for a year. Last week, Kato Road reopened on the Fremont-Milpitas border after being closed nearly a year so it can be routed under the BART tracks.

For the most part, however, the construction has been barely noticeable. That is about to change in a major way for the $2.3 billion, 10-mile route from Warm Springs in South Fremont to Berryessa Road in San Jose.

The goal is to beat the projected 2018 opening date by a year.

"That's what it is looking like," said Carolyn Gonot of the Valley Transportation Authority and the project manager for the BART extension. "Right now, we're on schedule to hit 2017."

Work has gone smoothly so far. More than 100 public meetings have been held to keep nearby business owners and residents up to date.

And here is what they've been hearing. Hostetter Road will be partially closed beginning Monday and in the summer Warren Avenue will be closed. Soon after, crews will be digging under Dixon Landing Road, Montague Expressway, Trade Zone Boulevard and Capitol Expressway, where BART tracks will be installed.

More than 33,300 truckloads will move 850,000 cubic yards of dirt. And 21,570 tons of steel will be put down, along with 200,000 cubic yards of concrete and 100 miles of wire for power and communications equipment -- all within Santa Clara County.

"This work is going to be very visible to the public," said Bernice Alaniz, a VTA spokeswoman. "There will be a lot going on in this second year -- demolition of buildings and trenching work."

BART will go underground north of Montague. A station there will serve as the transfer point for riders who want to take light rail to the many high-tech companies along Tasman Drive.

North of Berryessa Road, BART will rise 35 feet above ground level and remain elevated past Mabury Road before the line ends near Highway 101.

The entire 15-mile line from Fremont will cost $3.2 billion, with the Alameda County portion of the line scheduled to open in late 2015.

Rep. Mike Honda, D-San Jose, called the project a "shining example of how vision and determination in a community can have immense impact." Planners have wanted to bring BART to San Jose for 40 years, and it became possible when voters in Santa Clara County approved two taxes by two-thirds margins to pay for building the extension and operating the trains. That second tax was key to securing $900 million in federal money from the Department of Transportation.

Motorists also will benefit. Congested Mission Boulevard will be widened to three lanes near Warm Springs, easing the bottleneck on one of the South Bay's most heavily traveled roads and the main commuter link between Interstates 680 and 880.

And gone will be all those nasty, street-level crossings that Union Pacific freight trains once used.

Someday, BART boosters hope, the line will extend six additional miles through downtown San Jose, ending at the Caltrain depot in Santa Clara. However, that final stretch will require building a tunnel under Santa Clara Street and will cost $4 billion. The VTA is $2 billion short, and no timetable has been set for the work.

Contact Gary Richards at 408-920-5335.