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.
In large part, this increase in Caltrain popularity and usability was because of the Caltrain Peninsula Joint Powers Board’s popular Baby Bullet program which was introduced in 2004. By skipping some stops, the Baby Bullet trains provide both faster service for longer distance travelers, and good local service for shorter distance travelers. By 2019 Caltrain was operating 92 weekday trains with 22 of those being Baby Bullet trains.
Bay Area Transportation Working Group 