The Santa Clara Valley Transportation Authority recently increased the budget for its BART Silicon Valley Phase II extension to a staggering $9.3 billion.

That would be more than $1.5 billion for each mile of the six-mile project from the Berryessa station through downtown San Jose to Santa Clara. There are not enough greenhouse gas emission savings or rider convenience benefits to justify the cost.

The per-mile cost approaches levels reached by New York City’s troubled Second Avenue Subway. But compared with that project, the BART extension would serve a less-densely populated area where residents are less inclined to use public transit.

VTA estimates the extension would serve 52,000 average daily riders, but most of them would switch from other transit modes like bus and light rail. According to VTA’s Environmental Impact Statement, the extension would generate only 14,600 new transit trips, mostly by inducing drivers to leave their cars.

But even these projections are based on a 2012 ridership model, and thus do not reflect behavioral changes arising from the COVID-19 pandemic. Pre-pandemic ridership forecasts have proven unreliable: In a 2010 Environmental Impact Statement, VTA projected average weekday ridership of 41,800 on the Phase I BART extension, which added stations at Milpitas and Berryessa. But in October 2022, those two stations recorded an average of only 2,261 weekday exits.

So, the Phase II extension would replace a few thousand car trips each day at most. And, by the expected 2034 opening date, the line would be attracting many drivers who might otherwise be using electric vehicles. By 2034, state law calls for 94% of new-car sales to be zero emission vehicles or plug-in hybrids.

The new BART service would offer more options along the six-mile extension, which is already served by buses and trains. But time savings using BART would be limited by long escalator rides down to the lower platforms 86 feet below street level.

While the most cost-effective solution is to simply stop work on this extension, VTA has plenty of sales tax proceeds and the will to proceed. So let’s consider a scaled-down extension.

The most obvious economy is to terminate service at Diridon Station rather than to run parallel with existing Caltrain service to Santa Clara. With electrification being completed later this decade, Caltrain will have sufficient speed and capacity to meet travel needs between Diridon and Santa Clara.

Another option is to build only the first station at 28th Street/​Little Portugal. Besides saving money, this option would save businesses along East Santa Clara Street from construction-related disruption. Local and express buses serving this thoroughfare could provide frequent connections between the new BART terminus and downtown Diridon. VTA could scale up bus service if sufficient demand materialized.

Unfortunately, the willingness and ability to perform the cost/​benefit analysis necessary to right-size new projects eludes Bay Area transit planners. The San Jose Phase II extension was planned decades ago and is proceeding on autopilot, regardless of whether stagnant population, increasing remote work or a shrinkage of tech sector employment might impact ridership and thus the benefits the project can be expected to provide.

This disinterest in balancing costs and benefits also explains why planners are going full steam ahead with a second transbay BART tunnel for $29 billion, and a 1.4‑mile connection between San Francisco Caltrain Station and the Salesforce Transit Center at a cost of $5 billion despite the collapse in commuting to downtown San Francisco. Including the San Jose BART extension, these big-ticket projects will cost $43 billion (before overruns) and provide no transit benefits whatsoever for 10 or more years.

Bay Area residents and federal taxpayers, who will shoulder much of the bill, deserve better.