For years, South Bay transportation officials boasted that construction of BART’s extension into Santa Clara County was several months ahead of schedule and that it would probably open late in 2017, but they acknowledged Tuesday that those predictions may have been overly optimistic.

The first BART train won’t cross the Santa Clara County line early after all. Instead, it should arrive at its originally scheduled time — June 2018 — they said, so please don’t call it a delay.

“It was forecast for early completion,” Brandi Childress, a VTA spokeswoman, said of the 10-mile extension. “But now we’re saying that is not going to happen.”

Almost since the start of construction of the 10-mile extension in April 2012, officials with the Santa Clara Valley Transportation Authority, who are overseeing the project, had boasted of being six months ahead of schedule and on track for a late 2017 opening. In the past year, they spoke of it with near certainty.

But after a series of meetings with BART officials this summer, VTA officials have reverted to the originally scheduled opening in June 2018, a date set by federal transit officials who helped foot the project’s $2.3 billion bill.

Back to Gallery BART pulls forecast for early completion of Silicon... 5 1 of 5 Photo: James Tensuan, Special to The Chronicle 2 of 5 Photo: James Tensuan, Special to The Chronicle 3 of 5 Photo: James Tensuan, Special to The Chronicle 4 of 5 Photo: James Tensuan, Special to The Chronicle 5 of 5 Photo: James Tensuan, Special to The Chronicle









Under a first-of-its-kind agreement, the VTA is building the extension from Warm Springs in Fremont south to stations in Milpitas and the Berryessa neighborhood of East San Jose. After it’s tested and ready to go, the authority will hand it over to BART to connect it to the existing system and to run the trains.

But that’s going to take longer than the next couple of months, said John Engstrom, project manager for the Silicon Valley extension.

While construction crews apply the finishing touches to the two new stations, which should be completed by year’s end, VTA needs to complete testing of train control, communications and other systems with and without trains running on the new rails.

Once that’s done, VTA will turn it over to BART, which will perform even more rigorous tests designed to ferret out any possible problems, Engstrom said.

“Basically, we try to break it,” he said. “It’s better to have it break during testing than when trains are running.”

Once the glitches have been worked out, the final step before BART can start carrying passengers to and from Silicon Valley is certification from the California Public Utilities Commission.

Testing is already in progress, Engstrom said, and no particular problems have emerged. But he said the job of making certain complex systems work together, and as they’re supposed to, can be painstaking and time-consuming.

“I think of it as a 10-mile-long robot,” he said, explaining that each element must be tested separately and in conjunction with others.

The announcement of next June’s opening was made Tuesday amid the dust and noise of construction at the Milpitas Station, near the Great Mall shopping center. The station, featuring a wave-shaped roof perforated with three large skylights, looks almost ready to go.

The tracks, third rail, elevators and escalators are in place on the subterranean platform level, and the fare gates are installed, covered in plastic, near the arched entryways. A six-story parking garage sits empty, but ready for use, with the stripes and numbers painted on the pavement. A bridge linking the station with a VTA light-rail station stretches across Capitol Avenue.

South Bay residents who want to ride BART now have to drive to Fremont, where the downtown and Warm Springs stations are located, or ride a VTA express bus from the Great Mall to the downtown station.

Andrew Favian, 29, of south San Jose, waited a half-hour for the bus, then took the 20-minute ride to the station. He looks forward to BART’s arrival in Milpitas, even if it isn’t until June.

“I could have been in Pleasanton by now,” he said. “With BART, it’s a direct route. You don’t have to wait for the bus and then wait for BART. It will be a lot more convenient.”

Michael Cabanatuan is a San Francisco Chronicle staff writer. Email: mcabanatuan@sfchronicle.com Twitter: @ctuan