Environmental impact advantages are detailed near the end of this Q&A. The Altamont routing has more potential to serve a lot more needs:
The following two maps show and give comparisons between the route alternatives:
This would be much more costly. Upgrading the 88 miles of the corridor between Sacramento and Oakland (and possibly another 45 miles to San Jose) would serve that corridor exclusively, with even more total route miles than the Diablo and Pacheco alternatives. Bay Area-Sacramento service via Altamont would not require this additional 88 miles of high speed track because the service would use the same routes as those used for service to Southern California. This would maximize the number of markets served (short and long distance, north-south, east-west), and require the fewest track miles that can be up and running the soonest. Moreover, the Altamont route would provide direct transbay service from Sacramento to San Francisco, as well as to SFO airport. Perhaps a built-out HSR system eventually will include the Capitol Corridor with new Bay crossings for trains at Vallejo and between San Francisco and Oakand. But that is not likely to be built for decades.
How would HSR serve San Jose if the Altamont route were chosen?
If Altamont were chosen, San Jose and San Francisco would be at the ends of separate branches -- a scenario similar to the four branches of the BART system serving the East Bay. San Jose would not receive worse service or less service, compared to its service under either the Pacheco or Diablo Direct alternatives. The San Jose branch would be included in the phase one system. BART's four East Bay lines all run at high frequency, and their schedules merge together to operate through the Transbay Tube without scheduling difficulties. HSR lines, notably Germany's HSR network [see map], operate on branching networks of comparable complexity. Every Northern California branch can have some trains running nonstop to LA, and some stopping at intermediate stations. Market demand will determine how many of each service grade San Jose (and San Francisco, Sacramento) will have heading south.
While Altamont would mean that travel times and distances between San Jose and southern cities would be slightly longer, it would offer other advantages even for San Jose. Because San Jose would be an endpoint on its own line, it would have its own dedicated trains to Southern California, as well as Sacramento. Passengers from San Jose would board empty trains that are waiting at the station at the start, instead of having to find a seat on a train that would stop only briefly and would already be two-thirds full. Frequency to San Jose would be adjusted independently of frequency to San Francisco, based on ticket sales from San Jose and other Bay Area stations. In this way, trains could run consistently full from end to end (SF-to-LA or SJ-to-LA) and operation would be more cost-effective.
Studies have shown conclusively that San Francisco will have the highest HSR ridership of all Northern California cities. SF should have nonstop service to Southern California, and these trains should have a way to bypass San Jose. Estimated running times of less than three hours are for these nonstop runs. Under the Pacheco and Diablo Direct routes, these trains would pass through San Jose. This would require passing tracks through the San Jose station. Trains will not be allowed operate at full speed through urban areas including San Jose. Due to this problem, the 1996 High Speed Rail Commission study and the California High Speed Rail Authority's 1999 comparison found that SF-LA travel times would be slightly faster via Altamont.
The San Francisco branch of the Altamont route would cross the Bay between Fremont and Redwood City. Wouldn't a new bridge be costly and have serious impact on wetlands?
The Dumbarton rail bridge, the oldest bridge to span the Bay, already crosses at that location. A plan is in place to restore passenger service on this line. Environmental problems are far more serious on the San Jose-Fresno mountain crossings studied in the 2004 EIR. The Altamont route across the Diablo Range into the Central Valley would stay almost entirely within already developed areas. In contrast, the Diablo Direct and Pacheco routes would pass through remote regions of the mountains, as well as wetlands in the San Joaquin Valley near Los Banos. Much longer segments of the latter routes would traverse such areas compared to few miles where the Altamont route would cross Bay wetlands.