The estimated price of building the 4.8 mile BART extension through San Jose has increased again. It’s now up to $6.86 billion and rising. This all started because of downtown demands that the entire subway be built with no construction impact on Santa Clara Street. This short-sighted demand apparently stemmed from the misguided belief that constructing the two downtown stations using the standard cut-and-cover methods used all over the world for station construction would bring Santa Clara Street to a halt for the entire 4 to 6 year construction period. This is not true. As shown in the section below, at no time would the street be entirely closed. Here’s how it’s normally done. First, one half the street is excavated and decked over, after which the traffic is shifted to the decked half while the other half of the street is similarly excavated and decked. This phase of the project can be completed in a relatively short amount of time. Once the wooden decking is in place and traffic again flowing, the major below-grade construction work begins. At the end of the job the permanent new roadway is reconstructed, again in a relatively short amount of time and again while keeping at least half the street operating at all times.
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Acceding to the demands for no disruption, the City of San Jose decided to abandon the traditional way of building subway stations in favor of a largely untried all-tunnel construction program. The idea was to keep the construction of the subway entirely below grade and out of sight even at stations. This ill-considered and short-sighted departure from the normal way of building subway stations, lead directly to several other decisions that only compounded the problem. To tunnel the entire subway including the stations it was necessary to replace the two originally specified 20-foot tunnels with a humongous 48-foot diameter hole along 2.6 miles of the subway, thereby increasing the amount of excavated material to be hauled away by an estimated 65,000 truckloads. Increasing the size of the tunnel also required a major increase in the thickness of the concrete tunnel lining and elaborate underground transition structures at each end of the large bore tunnel section. In order to avoid an even larger tunnel it was necessary to place the station tracks at different levels, thereby requiring the addition of two 900-foot long emergency egress platforms. Despite the platforms, the escape routes are expected to be harder to follow in a crisis, thereby putting BART riders at greater risk.
As currently planned the bottom of the subway would be 100 feet (ten stories) below grade. Escalators, elevators, emergency stairways and all other connection to the surface would need to be lengthened accordingly, thereby further pushing up construction and future maintenance costs. To further reduce disruption during construction the entrances to the Downtown Station are to be located only on the north side of the street, even though most train riders would be coming from the south.
The plan to extend BART service northward from the Diridon Station along the Caltrain tracks all the way to the Santa Clara Caltrain Station would further increase both capital and operating costs.
These decisions have substantially driven up the cost of the project. In February of 2018 it stood $4.8 billion. By March of 2020 it had jumped by 17% to $5.6 billion. In the past six months it has increased by another 22% and now stands at a staggering $6.86 billion. Are there more increases ahead? Almost certainly.
The VTA’s subway needs a fresh look, conducted by an independent group of cost, construction and tunneling experts. Could the mistakes alluded to above be corrected? Yes, so far everything still is on paper. What could change? The Diridon and Downtown BART stations could be built using traditional cut-and-cover methods. The east bound and westbound tracks could be side by side, separated in the stations by 35-foot wide loading platforms, thereby obviating the need for both the emergency platforms and the transition structures. Instead of one tunnel the size of a five-story building, there could be two tunnels each 20 feet in diameter. Allowing the subway to be at least 30 feet closer to street level would further reduce costs (to say nothing of the ardor of climbing to the surface during escalator shutdowns). The subway could and should be accessible from both sides of Santa Clara Street. These changes would shorten the construction period, substantially reduce costs and bring about a safer and better subway operation.
The short-sighted decisions caused by over-emphasizing construction effects should be replaced with sound engineering. Construction impacts are short-lived. Subways are built to last a thousand years.