The rubber is finally hitting the road for California’s elaborate sustainable planning model, known commonly as SB 375. Nearly three years after the landmark environmental law was enacted, local governments are beginning to adopt the complex strategies required to implement it.

Two weeks ago, the San Diego Association of Governments adopted a draft Regional Transportation Plan, forecasting investments in streets and highways over the next several decades. The plan is part of a routine cycle prescribed by state and federal law since the 1960s. But in this interval, San Diego’s RTP has a new chapter: a Sustainable Communities Strategy, designed to reduce greenhouse gas emissions from cars and light-duty trucks.

The strategy’s goal, required by SB 375 for every region of the state, is to lower traffic-related emissions by giving residents more alternatives to driving.

In theory, the Sustainable Communities Strategy will drive a new growth pattern that better supports public transit and moves employment centers closer to homes. The strategy is designed with hooks in virtually every aspect of local general plans, and compelling incentives (a “get out of CEQA free” card) to pull those general plans into harmony with a sustainable vision for the future.

Tactically, the goal is integrating different policy priorities in one process (housing, transportation, natural resource protection), and getting planners to think more regionally. Strategically, the goal is hitting those emission reduction targets and promoting a diversification of transportation options and development types.

Now that the targets are set, local and regional agencies are beginning the tactical work of each developing a Sustainable Communities Strategy.

The San Diego Association of Governments has to go first. Because the SB 375 process is synced to the housing element cycle and SANDAG is next in the housing element lineup (prescribed in state law), California’s southernmost region has the distinction of adopting its climate change strategy before any others.

SANDAG will be followed by the Southern California Association of Governments, then the Association of Bay Area Governments, and later the Council of Fresno County Governments, Kern County Council of Governments, and Sacramento Area Council of Governments, followed by others.

The work of developing these plans brings a new focus on the synergy between housing and transportation policies, and how it affects climate change in the long run. Growth projections are becoming more robust and interdisciplinary. COGs and public-private collaboratives are getting more proactive in creating regional blueprints, or “visioning documents” – in many cases, a test prototype of the Sustainable Communities Strategy they will eventually have to adopt.

Cities and counties are also thinking more inter-jurisdictionally. Blending housing and transportation policies creates a crosshatch of the junctures where local and regional agencies have to cooperate. So the intersection of local and regional policies multiplies.

Local governments have been collaborating across city boundaries for a long time, such as in the federally funded regional blueprint process. As early as 2004, SACOG unveiled its “Preferred Blueprint Scenario,” a single document that accounts for transportation and land use policies for the entire region. (I still remember when a Yolo County Supervisor showed me the plan that December, proudly anticipating its creation could be become a model for the state).

Four years later, SACOG adopted its RTP using the Preferred Blueprint Scenario as its basis for land use and transportation investments.

SACOG’s blueprint scenario gives the Sacramento region a strong first step toward the SB 375 goal. Other regions have similar “first step” documents, such as the Association of Bay Area Governments’ “Initial Vision Scenario” and the Kern County Council of Government’s “Kern Blueprint.”

But for the first time, such regional scenarios will be expected to reach quantitative targets related to greenhouse gases. That mandate will drive regional planning into areas that have initially resisted it, and may compound the problems of jurisdictional politics and jealousies that can make cooperation such a difficult process.

A recent skirmish in Marin County, over how much of the region’s housing needs should be shouldered by the City of Novato, portends the kind of tensions that can bubble up even more fiercely when transportation plans are layered on top.

Ultimately, planners may be reminded of why housing and transportation evolved in separate silos in the first place: Because they are complex, and each deserved its own universe to balance competing priorities.

But in the logic of SB 375, the state can no longer afford this division of planning.

The law uses a mix of mandates and incentives. First, it directs the State Air Resources Board to assign to each region a specific target for that region to lower traffic-related greenhouse gases. And the Board has been doing this over the last few years.  San Diego’s targets, for example, are cutting 7 percent by 2020 and 13 percent by 2035.

Next, the law requires every Metropolitan Planning Organization to produce a Sustainable Communities Strategy that meets those targets. The strategy must also integrate the area’s Regional Transportation Plan with its Regional Housing Needs Assessment (it will be adopted, technically, as part of the RTP).

Once a strategy is adopted, public and private projects that comply with it are allowed to bypass substantial portions of the CEQA review process.

Commutes have been growing longer, and tailpipe emissions account of nearly one-third of California’s greenhouse gases. If local agencies are going to resolve the outward march of sprawl and provide residents with more transportation options, they’re going to have to work together, and talk about streets and rooftops in the same conversation.

The time to start that conversation is now.

Josh Rosa is a Sacramento Housing and Redevelopment Commissioner