After seeing the high cost and difficulty of putting high speed rail deep underground in the San Jose Diridon Station area, the City of San Jose has requested HSRA to study a shallow undergound option in hopes to reduce cost and improve constructability.
Under the shallow tunnel option, rail tunnels leading to and from the station would be built using tunnel boring machines. At the station area and the station approaches where the tracks join, the underground structures would be build by cut and cover. The shallow underground alternative has a similar alignment as the deep tunnel alternative, where the station would be located diagonally in front of the current train station.
The advantage of the shallow tunnel is that it costs $1.3 billion rather than $3 billion, but that's where the advantage ends. Under that alternative, the HSR station would have be dug out under the current light rail tunnel in front of the station and would have to occupy the land under the proposed baseball stadium, which is to be located south of the train station.
Deep tunnel option (upper) and shallow tunnel option (lower)
The shallow tunnel alternative would require changes to the BART project. Under that scenario, the BART tunnel would run under the proposed HSR tunnels rather than over it.
Because VTA has no funds to build BART beyond Berryessa, switching positions between the two rail lines is a feasible option. What VTA should also consider is to drop the redundent portion between San Jose Diridon and Santa Clara stations entirely. However, even if VTA is willing to address that issue, the conflict between cut and cover construction and the proposed stadium would likely kill this alternative.
Another option the city requested to study is to route HSR over the freeways rather than following the existing Caltrain corridor. Although this option has constructability concerns because of the need to maintain traffic flows on the freeway, it also presents an opportunity to build an iconic bridge for San Jose. As long as that iconic bridge does not end up to be another Bay Bridge fiasco, it might be the most reasonable option. With this option, the city would make HSR a part of the city's identity rather than to hide it.
Some of the cities further north on the peninsula are fighting HSR by pursuing another lawsuit against HSRA (HSRA already lost the first one). If San Jose is truly interested in HSR, it needs to decide how to accommodate HSR without adding more costs to the project.