The only way for the Bay Area to become a relatively affordable place to live again is for cities and counties to be more tolerant of different types of housing, according to the draft of a new regional plan.

This could include a requirement that at least 10 percent of new units across the region be affordable and requiring fewer parking spaces in new housing complexes. Some cities might need to increase the amount of housing allowed in areas with ample transit.

“We’re looking at what it would take the region to change the dynamics” that in recent decades have seen the creation of housing lag far behind job and population growth, said Matt Maloney, a planner with the Metropolitan Transportation Commission, which is working with the Association of Bay Area Governments on the document. “The housing crisis right now is what comes at you front and center.”

Known as Plan Bay Area 2040, the draft released this month also spells out spending priorities for what is estimated to be $303 billion in transportation funding during the life of the plan.

Much of the investment would go to projects that have been in the works for years, such as new ferry service and an expansion of “express lanes,” where single drivers pay for the privilege of using carpool lanes. The improvements listed include wider highways in Solano County and a new BART station in the Irvington district of Fremont.

At least $12.5 billion of the sum, generated by state and federal funding as well as voter-approved initiatives and gas-tax revenue, would be a local contribution to the high-speed rail effort. Other potential and controversial expenditures are not approved, such as “congestion pricing,” a toll that would be charged to drivers entering downtown San Francisco during commute hours.

The plan is mandated by the state, which in 2008 passed climate change-related measures that include a call for metropolitan regions to map out how they can reduce greenhouse gas emissions while making room for substantial amounts of new housing. The Bay Area agencies added 11 other targets to aim for in the regional plan approved in 2013 — many of them tied to social equity, such as cutting by 10 percent the amount of income that low-income families need to spend on housing and transportation.

The new draft, which is more of a progress report than a full-blown rethink of the plan, finds the Bay Area is on the right track in nine of 13 areas, including the protection of the region’s agricultural land and a boost in transit use instead of cars. But the region is projected to see the strain on less-wealthy residents grow, including an increase in the amount of family income needed for housing and transportation climbing from 54 to 67 percent.

The draft calls this glimpse into the future “particularly disconcerting” and “far off-trajectory.” It also argues that “to truly address affordability and equity challenges, an engaged public and government at all levels will need to act.”

This is where ideas like including affordable units in all new housing developments comes in, or the density boost in areas where the 2013 plan calls for increased growth.

“Our scenario is to try and motivate more growth in areas that local governments already have identified,” Maloney said. At the same time, he acknowledged that the regional agencies can only cajole, not compel. There can’t be a decree to do away with parking minimums across the Bay Area, for instance.

“This is a regional blueprint for growth,” Maloney said. “It’s certainly not meant to usurp local control.”

That was the perception the first time around: Plan Bay Area drew opposition from local Tea Party activists, along with organizations as disparate as the Sierra Club and the Building Industry Association of the Bay Area. So far, though, the update seems to be moving forward without fireworks.

“It’s surprising, and heartening, to see that there hasn’t been the same controversy,” said Matt Vander Sluis of the Greenbelt Alliance, a nonprofit that works to combat sprawl.

The commission and the association will hold an additional set of workshops on the draft plan this spring. The draft environmental impact report will be released Monday. An approval of the update could come in midsummer, after another round of workshops in the nine Bay Area counties.

As for the 13 targets — which this month’s draft describes as “aggressive and ... quite aspirational,” Plan Bay Area supporters take the mixed grades in stride.

“It’s helpful to have clear targets for what we want the region to be,” Vander Sluis said. “They set a direction, and show whether we’re doing enough to get there. And in this case, it points out that much more is needed.”

John King is The San Francisco Chronicle’s urban design critic. Email: jking@sfchronicle.com Twitter: @johnkingsfchron

Learn more

For more information on Plan Bay Area 2040, including the full document and a schedule of public meetings: www.planbayarea.org