Last week the city council in Mountain View, California, took a significant step toward addressing Silicon Valley's housing affordability crisis. According to the Mountain View Voice, the city council "largely gave a thumbs-up" to a new planning document for its North Bayshore district that envisions the creation of up to 10,250 units of high-density housing, though further review will be needed before the document is final. Mountain View only has about 32,000 households total, so that would be a substantial 32 percent increase.

The council's new direction is a victory for Google. The search giant has its headquarters in the North Bayshore district, owns much of the land in the area, and has long been lobbying for more housing near its sprawling corporate campus. If private developers (or perhaps Google itself) step up to realize the new vision, it could allow thousands of Google employees to find housing within walking distance of their jobs, making Google a more attractive place to work.

The big question is whether this represents an isolated victory for housing advocates or whether it's the start of a trend toward denser development in Silicon Valley more broadly. Mountain View's about-face came after voters elected a new pro-development city council in 2014. If voters in nearby municipalities elect pro-development leaders as well, it could lead to dramatic changes housing and transportation policies across the region.

Housing growth has become a hot topic in Mountain View politics

Over the past two decades, the growth of Silicon Valley's technology sector has produced a steadily worsening housing situation. Companies like Google and Facebook have minted hundreds of millionaires and provided high-paying jobs for tens of thousands of people. The supply of housing hasn't kept up, and housing costs have skyrocketed.

Affordable housing advocates have urged Mountain View to allow more construction. They've had an ally in Google, which recognizes that astronomical housing costs and long commutes make Google a less attractive place to work and has sought permission to build apartments near its corporate campus.

But until recently, the city council wasn't interested. In 2014, the city council approved a plan for the North Bayshore district that would have allowed the construction of even more office space in Google's backyard — but no new housing units.

That proposal became a major issue in the 2014 city council elections. Voters elected three new pro-housing members to the seven-member city council, giving advocates of housing development a majority. Over the past year, that new majority has reshaped the plans for North Bayshore to make them friendlier to new housing.

It will take years for developers to realize Mountain View's vision

Mountain View is a suburban community replete with detached single-family homes and strip malls. A new planning document prepared by city staff for last week's meeting envisions a very different future for the city's North Bayshore district.

In the core of the new high-density zone, developers could be allowed to build residential buildings as high as 12 stories. At the edges, apartment buildings would be limited to five stories to avoid having them loom over the existing structures.

And these towers won't be surrounded by huge parking lots. Instead, the city will encourage walkable, mixed-use neighborhoods with retail space at street level. Mountain View planners envision creating "opportunities for more active pedestrian street life with strong pedestrian oriented urban design elements such as storefront windows, entries, awnings and canopies, and street activity such as cafés, outdoor seating, and bicycle and pedestrian amenities."

Developers could be allowed to build residential buildings as high as 12 stories

The big question now is whether private developers are interested in actually building all of those housing units. Given the astronomical housing costs in the area, building new apartment buildings should be a highly profitable enterprise. But according to the Mountain View Voice, only two companies — Google itself and a housing developer called Sobrato — have expressed interest in doing it.

One reason may be that high-density developers would be required to offer up to 20 percent of their units at below-market rates. Developers will also have to comply with the city's elaborate vision for the new walkable neighborhoods, which could include open space, ground-floor retail options, and limits on parking.

The city is insisting on these kinds of requirements because officials believe they're necessary to develop a viable walkable neighborhood. The high-density North Bayshore developments will be surrounded by more car-oriented, suburban neighborhoods. They will need a critical mass of pedestrian-friendly housing, shops, and transportation options to turn North Bayshore into a viable neighborhood.

Transportation will be a big challenge for growing Silicon Valley

Mountain View's new plan for North Bayshore is an impressive step toward expanding the city's housing supply. But of course 10,000 new housing units is a drop in the bucket for Silicon Valley as a whole, with around 3 million people. To accommodate the growing demand for housing, Mountain View is going to have to approve higher-density projects in other parts of town, and neighboring municipalities will have to follow its lead.

The elephant in the room here is transportation. Silicon Valley is heavily car-oriented, and the region's roads are already clogged up. In the short run, expanding housing near Google's headquarters may relieve traffic congestion by reducing the number of people commuting from far away. The city's plan includes measures — like parking limits and amenities for pedestrians and bicyclists — designed to encourage people to take alternative transportation modes to work.

But in the long run, a growing Silicon Valley population is going to need a more efficient transportation system. Eastern cities like New York, Boston, and Philadelphia have an unfair advantage here. They were largely developed before the invention of the automobile, and as a result they have efficient rail networks that carry people to well-defined central business districts.

Silicon Valley has nothing like this. Its businesses are spread out fairly evenly across the region, a development pattern that makes sense if most people are commuting by car. Not only would building new rail lines today be fantastically expensive — since lines would have to cut swaths through some of the most expensive real estate in the country — but it's also not clear where the lines would go, since Silicon Valley doesn't have much of a downtown.

Silicon Valley does have one commuter rail line: the Caltrain that runs through Mountain View and other Silicon Valley towns on its way from San Jose to San Francisco. Right now, Caltrain only runs about every 20 minutes during morning rush hour, limiting its value for commuting.

Also, the Mountain View station has a large parking lot on one side and a wide four-lane road, making it unattractive for pedestrians. And the area around the Mountain View Caltrain stop is fairly low-density, which means there are few homes or offices within walking distance.

Doing the infrastructure work and staffing changes necessary to turn the Caltrain commuter rail service into a real high-frequency mass transit route would be a big first step toward making the region less car-reliant. Ideally, this would be accompanied by zoning changes that would allow higher-density housing and office space to be built immediately adjacent to the station.

But the bulk of Silicon Valley businesses — including Google's corporate headquarters, which is almost 3 miles north of the Mountain View station — are not close to Caltrain stops. So Silicon Valley's solution to this problem is likely to look different than New York or Chicago's.

Perhaps tech companies will find ways to extend the "Google bus" model to carry people between islands of high-density housing in an ocean of suburbia. Or maybe the advent of self-driving cars and smartphone-based ride-hailing apps will allow the invention of a completely new model, such as highly efficient carpooling or dynamically routed buses.

Regardless, the only way to figure it out is to start experimenting. And Mountain View's North Bayshore plan is an important step in that direction.

Correction: This story originally suggested that the city had given its final approval to the new plan, but the council's approval was only preliminary.

Disclosure: My brother is an executive at Google.