At what some describe as a make-or-break juncture for downtown Mountain View, the city is pressing ahead with plans to steer Castro Street toward a pedestrian-friendly future.

At its Tuesday, Dec. 10, meeting, the City Council approved a new set of studies for closing off Castro Street at the Caltrain tracks and potentially blocking off sections of the street to traffic and creating a pedestrian promenade.

In 2016, city leaders decided closing off Castro Street was the best option available to preserve the character of downtown while performing needed upgrades to the train crossing. As Caltrain prepares to launch faster and more frequent train service, Mountain View and other Peninsula cities have been urged to prepare grade separation projects, removing locations where auto traffic crosses over the train tracks.

The most obvious way to accomplish this, tunneling Castro Street under the train line, was expected to cost $120 million, and city officials decided it would be too expensive and disruptive. Instead, they favored a cheaper alternative to block off Castro Street at Central Expressway and build a new underpass for pedestrians and cyclists. Vehicle traffic heading into downtown would instead be routed along Shoreline Boulevard to Evelyn Avenue.

Now three years later, the plan remains controversial among downtown residents and business owners. Skeptics have warned that if plans are poorly implemented, it could ruin the charm of Mountain View's downtown.

Those concerns popped up again on Tuesday night, as council members reviewed a new environmental study for their multifaceted plans for the Castro area. The study, a mitigated negative declaration, essentially served as an official report affirming that the disruptive impacts caused by the Castro Street project would ultimately be balanced out. Barely anyone at the meeting disputed the study's findings, but the report still elicited many familiar concerns that fiddling with the layout of Mountain View's successful downtown carries big risks.

Councilwoman Alison Hicks, who previously worked as a city planner, did not mince words to describe what's at stake.

"I see the grade separation and underpass, it could potentially wreck the walkability of the downtown, or be an opportunity to make it much better," she said. "As we change the traffic situation ... how will that interface with the most popular walkable block in the city?"

Public works Director Dawn Cameron fielded questions about the project as best she could, although she pointed out that many aspects are still undetermined. By next spring, city engineers expect to be one-third finished with the design for the project. Part of the uncertainty is that Mountain View is still negotiating an agreement with Caltrain and the Valley Transportation Authority (VTA), which is expected to be signed by March. Once that three-way deal is finished, the grade separation project can move into its final design, with plans to begin construction in 2022. In any event, the city will eventually face a hard deadline to close off Castro Street because the train service will become so frequent that cars will no longer be able to cross, Cameron said.

For the project, Cameron pointed out the city should be able to make use of $60 million in VTA funding collected under the 2016 Measure B sales tax initiative. She said that Mountain View is well ahead of Palo Alto and Menlo Park in preparing its grade separation infrastructure.

"VTA said to us that since we're so far along, they'll consider us first in line for the funding," she said. "They've committed to funding this grade separation, but they haven't committed to the timing."

During the same meeting, the City Council also commissioned a new study to explore transforming a section of Castro Street into a pedestrian plaza. When complete, the study is expected to provide a variety of options for improving the pedestrian experience, which could involve a full or partial closure to vehicle traffic. The study is expected to focus on the 100 block of Castro, between Evelyn Avenue south to Villa Street.

After screening different planning firms, city officials decided to hire the San Francisco-based Gehl Studio for the study, at a cost of $265,000. The work plan for the study is expected to include up to three public meetings next year, and the City Council is expected to review a draft report by Gehl by in June.