Regional governments plan for 20 years of big growth, calling for dozens of road improvements.

Lucky for planners, humans move in a more orderly fashion than carbon molecules.

Since California lawmakers passed SB 375 in 2008, 22 regions have been crafting 20-year “sustainable community” strategies, which aim to reduce greenhouse gas emissions from vehicles 5 percent by 2035.

The Association of Monterey Bay Area Governments (AMBAG) board unanimously approved a plan June 11, projecting a population growth of about 20 percent from 2010-2035.

That means an additional 150,000 people on already stressed roads. The 200-page plan calls for 96 transportation projects in Monterey, San Benito and Santa Cruz counties, at a total cost of over $15 billion.

Improvements range from widening highways (to reduce traffic and car idling time) to laying light rail tracks and adding bike lanes.

The vision is bigger than just transportation: It’s about ensuring more people can live in the community where they work, which means re-allocating affordable housing.

David Pendergrass, mayor of Sand City, holds up his own tiny city as a densely populated, walkable example, where housing is available above commercial space.

“We’ve been doing smart growth, and didn’t even know we were doing it, since way back in the ’70s,” he says. “It’s easier for us than a sprawling metropolis.”

Still, Salinas City Councilman and AMBAG board member Steve McShane is optimistic.

“We now have a guide to housing-jobs balance, walkable and bikeable communities,” he says. “The danger: Like many government plans, it collects dust.”