MILPITAS — A key portion of the BART to Silicon Valley extension has been delayed by nearly a year, but it’s too soon to know if the timeline for the overall $2.3 billion rail line will be pushed off track.

The Valley Transportation Authority had planned to build a trench over the next eight months to prepare for future BART tracks under Dixon Landing Road just east of Interstate 880, on the northern edge of Milpitas. But the city has won its bid to allow a more gradual project lasting 18 months.

The fight between the transit agency and the city arose after VTA proposed a new plan to close a small stretch of the main east-west Dixon Landing thoroughfare during construction. That plan angered local businesses and city officials who say traffic flow on the road is already very difficult.

Last month, in an unusual move, the city of Milpitas denied VTA’s work permit request and told the agency to find a way to do the work while closing only part of the four-lane road, even if it means construction will take longer.

In a last-ditch attempt to get the permit, VTA filed a claim in Santa Clara County Superior Court but lost the case last week.

The 10-mile BART extension — from Fremont to North San Jose — had been on track to open in late 2017. The additional 10 months on the Milpitas leg could delay the first BART rides into Silicon Valley, but crews may be able to make up time in other sections of the rail line project.

“We won’t know until we get going, if there will be impacts to the overall schedule,” VTA spokeswoman Colleen Valles said Saturday. But she said the delay will not increase the cost of the project.

Valles maintains the community supported the full closure of Dixon Landing Road because it would decrease the amount of time the neighborhood would be inconvenienced. And the portion of road that would be closed, between Milmont Drive and just east of the existing freight line tracks, is so small — shorter than a typical city block — that the detour would only take drivers a couple extra minutes.

But city officials, speaking to this newspaper last month, said they were blindsided when the VTA in January proposed changes to their original agreement for a partial road closure. Milpitas saw no reason the transit agency couldn’t keep at least one lane in each direction open to ease what is already a bad bottleneck. Local businesses had blamed intermittent nearby roadwork from the project for costing them customers already, and feared the latest detours would be even worse.

City officials could not be reached for comment over the weekend.

The delay is a rare roadblock for the VTA, which had been ahead of schedule on the long-planned BART extension.

Over the last few years of construction, several other major road closures from Fremont to San Jose had been approved and, while they have annoyed drivers, they had not reached the drama of the Dixon Landing Road saga in Milpitas. Overall, there are 11 points at which the new tracks, running along the old Union Pacific line, will intersect with existing streets, requiring major roadwork.

Contact Mike Rosenberg at 408-920-5705. Follow him at Twitter.com/rosenbergmerc.