Beyond the Altamont Wind Farm, on former grazing fields that slope down to the flat floor of the San Joaquin Valley, builders are framing houses for the first wave of Tracy Hills.

The community pool will open later this month. Billboards indicate the future locations of the fire station and elementary school. Rolls of turf dot the terrain, ready to be unfurled into playing fields. Potted trees, soon to be planted, line the subdivision’s winding bike and walking trails.

Even in the midst of a climate crisis, the Bay Area’s skyrocketing housing costs are pushing families into far-flung suburbs like Tracy. And the American dream of a single-family home coupled with cities’ restrictions on building multifamily rentals and condos means “exurbs” continue to thrive despite state and local officials’ recognition that they exacerbate climate change.

The majority of buyers at Tracy Hills are families who work in the East Bay or Silicon Valley, but are priced out of those communities, said John Palmer, development manager for master developer Integral Communities Homes. Prices for the planned community of 4,700 homes start around $500,000 and top out just above $700,000 — well below the $850,000 median price of a single-family home or condo in the nine-county Bay Area.

“The city of Tracy is providing a housing supply for a need that is not being met in the core Bay Area,” Palmer said.

Palmer said the neighborhoods are designed to be as pedestrian-, bike- and transit-friendly as possible. Still, the development seems to go against all the state’s housing and environmental policies, which prioritize compact housing in already urbanized land near transit, jobs and services.

Subdivisions like Tracy Hills have gobbled up thousands of acres of agricultural land in the city, ballooning the population from 18,500 in 1980 to about 90,000 today, and it’s projected to rise to 125,000 by 2035.

Some 80,000 commuters now drive between the northern end of San Joaquin County and the Bay Area, 75% of them alone in a car over Altamont Pass to jobs in places like San Jose, Fremont or Pleasanton. Their drives average 120 miles round trip. Just 2.5% take public transit, according to the Bay Area Economic Institute.

The environmental impacts of so-called “greenfield development” that replaces farmland — which defines 80% of what’s built or approved in San Joaquin Valley — are well-known. Long commutes in single-occupancy vehicles means more greenhouse gas emissions.

Ethan Elkind, director of the climate program at the Center for Law, Energy and the Environment at UC Berkeley’s School of Law, said the spread of single-family homes in the Central Valley is directly related to NIMBY policies throughout the Bay Area, especially zoning that doesn’t allow multifamily buildings.

By the numbers 75% Share of San Joaquin County commuters who drive alone to work 50,000 Number of acres of San Joaquin Valley farmland that were developed between 2004 and 2014 18 Number of miles more that residents living outside of infill areas drive on weekdays compared with residents living in dense neighborhoods with transit. 1.79 million Metric tons of greenhouse gas emissions that would be reduced in California if the state’s next 1.9 million housing units are all built in infill areas. That’s equivalent to taking 378,000 cars off the road. 60% Share of California’s housing development that is infill; the rest is in nonurban agricultural areas. $312 The amount per year that every renter would save if closer to jobs and schools and had increased transit options Source: Terner Center for Housing Innovation, staff research The series This week, The Chronicle joins more than 200 news outlets worldwide in examining the impacts of global climate change, an effort that will lead up to a Sept. 23 U.N. summit on the topic.

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“The fact is that we don’t build (multifamily) communities ... in the Bay Area because they are largely illegal to build. Our policies are pushing development into the hinterland, creating a mega-sprawl region,” he said.

The sprawl continues even as the benefits of living in infill areas are well documented. Residents living in infill areas drive 18 fewer miles per weekday, according to a study from the Terner Center for Housing Innovation at UC Berkeley. Residents living in infill housing exercise more, spend less money on transportation, and have more time with their families.

The report assumes that California will need 1.9 million new units by 2030 to keep up with population growth. If those housing units were to be 100% “infill” projects — with no greenfield development — that would reduce greenhouse gas emissions by 1.79 million metric tons a year. That’s the equivalent of removing 378,000 cars off the road, according to the report.

As San Joaquin County makes clear, California has a long way to go to reach those goals. Currently, about 60% of the housing being developed in California is “infill.” In San Joaquin County, just 20% of development qualifies. Between 2004 and 2014, about 50,000 acres of San Joaquin County farmland was developed.

Back at Tracy Hills, Palmer says his team is taking pains to make sure the project is a new breed of greener and more urbane subdivision. The streets have 10-foot-wide sidewalks and narrow lanes for cars separated by a landscaped median. Bike paths connect the eight neighborhoods. Kids can bike or walk everywhere they need to go.

Two bus stops will be installed, linking the property to downtown Tracy and the Altamont Commuter Express train station, which runs from Stockton to San Jose. The Tracy ACE Station is about 3 miles from Tracy Hills. It would take no more than 20 minutes to bike to the ACE Station, where a train to Fremont takes about an hour. In addition, the project includes 250 acres set aside for retail, office and industrial development. The hope is that eventually families can live, work, shop and play at Tracy Hills.

“More pedestrian and bike networks, more transit stops, more co-locating multiple uses so you do have residential next to jobs and shopping,” said Palmer.

It’s unclear how many commuters will drive, as opposed to taking the transit options included in the community’s design. But experience suggests that a subdivision on former agricultural land an hour from major job centers is no one’s vision of smart growth. But given that these projects are being built, and will continue to be built, careful planning can limit their carbon footprint, said state Sen. Scott Wiener, D-San Francisco.

“If you are building housing that is accessible to public transit and that is walkable, then that is moving in a positive direction,” Wiener said. “It’s going to look different in different cities, but as long as you are connecting the dots among housing and transit and jobs and retail, then that is good.”

J.K. Dineen is a San Francisco Chronicle staff writer. Email: jdineen@sfchronicle.com Twitter: @sfjkdineen