As traffic and congestion plagues the Bay Area, regional transportation leaders are working on a redesign of the South Bay’s most critical transit hub: San Jose’s Diridon Station, abutting a potential new multi-million-square-foot Google campus.

Some details of the new station have been ironed out. For instance, train tracks at Diridon Station will eventually sit 25 feet in the air and riders will come and go via four exits between Santa Clara and San Fernando streets. But next month four key planning bodies will be tasked with making some of the most critical decisions yet related to the effort: how will the trains come and go through the surrounding community?

“We certainly acknowledge that this is a tough decision to decide on an alignment,” John Ristow, San Jose’s transportation director, told councilmembers. “We also know and acknowledge what these (abutting) communities have actually gone through over several decades of history –very large infrastructure projects that have impacted their neighborhoods.”

San Jose councilmembers Tuesday night got an early look at options for future track alignments at the station ahead of a Feb. 4 meeting, where city leaders are expected to decide which option they like best.

By 2040, regional leaders expect Diridon Station will exponentially grow its daily traveler capacity from 17,000 currently, up to 140,000 transit riders on a daily basis, rivaling the number of passengers that move through the San Francisco International Airport each day today.

The newly designed transit epicenter will be a key meeting point for the BART expansion, commuter and high-speed rail, local light rail and bus lines and is expected to open around 2030.

The station’s track alignment will also have far-reaching effects on surrounding communities, said Jessica Zenk, the city’s transportation options manager.

“The decisions that are made at and around the station have very far-reaching physical implications all the way as far north as the Caltrain Maintenance Facility all the way down south to Communications Hill,” she told councilmembers.

Both potential rail layouts include four train tracks, half of which will be electrified, allowing for high-speed rail service running through the station.

In one potential alignment, two tracks would run through the platform’s existing footprint, while the other two tracks would run on an elevated viaduct. The second layout includes a four-track option through the platform’s existing alignment and no viaduct.

Each option comes with advantages and drawbacks, but generally, allowing the trains to run only using the existing alignment would cost half the amount and have fewer negative impacts to the surrounding community overall, according to city documents. That’s why transportation planners are recommending that the alignment remain in the current alignment, not via an elevated viaduct.

Pros and cons of the two rail alignment options currently on the table for Diridon Station. Image courtesy of San Jose public records

Diridon Station sits in the middle of what is now a low slung area on the western edge of the city’s growing downtown, where industrial buildings, small businesses and single-family homes have co-existed for years, even through major freeway expansions and flood mitigation projects.

But the land around the station could become a major economic and housing hub in the coming decade if city leaders approve Google’s massive mixed-use development proposal and rezone the area for taller buildings. Those two efforts are underway now, despite some community concern about displacement and gentrification.

Notably, transportation leaders have also discussed the possibility of placing all four tracks on two viaducts, but discouraged the idea due to the increase in maintenance needs and negative effects on the environment, the visual landscape and property acquisition that it would risk.

“Given all these concerns and considerations, the partner agencies have concluded that placing all trains on the I-280 viaduct is a fatally flawed design option,” Ristow wrote in a memo.

But transportation leaders still said a viaduct option for two tracks was a feasible option, although the structure would still present several challenges.

After months of community feedback, many neighbors supported the idea of re-routing train traffic onto a new, three-mile long viaduct that would follow Interstate 280 and State Route 87, said Elizabeth Scanlon, the project manager for the initiative representing the four public agencies involved, which includes the California High-Speed Rail Authority, Caltrain, the city of San Jose and the Valley Transportation Authority.

Transportation leaders said the viaduct could divert train traffic away from the transit corridor and reduce noise and other negative effects on the surrounding Gregory, Gardner and North Willow Glen neighborhoods.

San Jose lawmakers will decide on a track option at its Feb. 4 City Council meeting.

Caltrain and VTA’s Board of Directors will decide two days later on Feb. 6. Lastly, the California High Speed Rail Authority Board of Directors will choose a preferred track option at its Feb. 18 meeting before transportation leaders move onto the next phase of the station’s plan.

Contact Nadia Lopez at [email protected] or follow @n_llopez on Twitter. Contact Janice Bitters at [email protected] or follow @JaniceBitters on Twitter.