A new look is coming to the old, midcentury boulevards that crisscross the Bay Area — gray gashes in the landscape designed for cars to cruise at 30 mph.

Now, as the Bay Area’s population and economy surges, and demand grows for more housing, roads like San Pablo Avenue in the East Bay and El Camino Real on the Peninsula have become anachronisms. These stretches of asphalt predate the rise of interstate freeways. Their monotonous scenery of drive-throughs, strip malls and gas stations represents a way of life that faded out a long time ago.

“In the 1950s, the 1960s — maybe even the 1970s — it kind of made sense,” said Matthew Lewis, an environmental consultant and spokesman for the pro-housing group California YIMBY. “But now it doesn’t work to keep adding cars to a finite space. The roads can’t get any wider, so the traffic just gets worse. And it’s extremely dangerous for cyclists and pedestrians.”

In the future, many of these transit spines will become civic spines. Chief among them is San Pablo, where the evolution is already showing in small ways: food trucks, yoga studios and craft breweries sprouting among the auto body shops, new bike racks beneath the restored Art Deco marquee of the Cerrito Theater. A lot that once housed a Guitar Center is cluttered with bulldozers, and a sign hangs on its concertina fence: “Coming soon: 32 condominium units.”

Bigger changes are coming to the street. Officials in Alameda and Contra Costa counties are gathering public input on the San Pablo Avenue Corridor project, which would remake 12 miles of blacktop from downtown Oakland to Richmond’s Hilltop Mall area. It hinges on the idea of moving people, rather than cars. Of the three concepts the Alameda County Transportation Commission has put forward, the most far-reaching would strip out a lane of traffic on either side of the road, adding bus-only lanes in the center and bicycle lanes adjacent to the sidewalks. To accommodate that redesign, planners would remove much of the avenue’s parking.

Tess Lengyel, deputy executive director of planning and policy at the Alameda County Transportation Commission — the agency leading the effort — described these ideas as “very early stage,” for a plan that could take 10 years, and endure many revisions. Her agency is looking at similar proposals for East 14th Street, another artery that extends from San Leandro into Hayward, where it becomes Mission Boulevard before cutting through Union City and Fremont.

This type of change used to cause anguish for residents and businesses. But now cities are taking the plunge, courting new development and swaddling long stretches of pavement with dense housing. The roads that linked Spanish ranchos in the 1800s and welcomed car culture in the 1900s are now entering their next phase.

“If we’re still around, we’ll definitely want a piece of that action,” restaurateur Gannon Abbey said about the coming development. Abbey co-owns Cafe Nine, a sandwich shop off San Pablo near the elevated BART tracks in El Cerrito. It’s squeaked by for 21 months, drawing patrons who sit at patio tables with their laptops, alongside a parking lot that also serves a bank and a weight loss clinic.

Abbey and other business owners are holding out for several housing projects that would bring thousands of new residents: a chunky apartment building with balconies at a former Mexican restaurant, another stack of apartments replacing a shuttered Taco Bell, a 124-room hotel and a sprawling complex next to the El Cerrito Del Norte BART Station. That’s just a sampling: Since 2014, the city has approved 13 projects with 1,600 housing units planned.

These days there’s more of an appetite for housing and dense development, owing to a generational shift in El Cerrito. New residents moving in from Oakland and San Francisco want to maintain an urban lifestyle, even as they seek suburban amenities like bigger homes and backyards.

“The population’s getting younger,” said El Cerrito community development director Melanie Mintz. “Walkability is more important. And people are pretty conscious of the housing shortage.”

That new population has also helped activate a retail node that struggled for years.

“The gentrification has been good for us,” said J.C. Garrett, a clerk at Down Home Music, a 43-year-old record store that specializes in blues, folk and Gospel — not the type of business that survives transformations of the neighborhood.

“All these younger techie people are coming in with their kids in strollers and spending money,” Garrett said. He gestured toward a natural food store across the street, barely visible through the store’s plate glass window. “That’s also been good,” he said. “We don’t have to eat Subway sandwiches or Jack in the Box for lunch every day.”

As attitudes evolve, city leaders in El Cerrito have rallied support for a land use plan the City Council approved in 2014, allowing new apartment buildings to sprout from lots that have long sat empty. While that development rolls forward, transportation officials are contemplating dramatic changes to the roadway geometry on San Pablo.

Developing the main drag of a suburb is one thing; reshaping a 12-mile, multicity corridor is another ordeal. If new residents of El Cerrito embrace the project, some of their neighbors are wary.

“All the generic housing that’s being built right now will change the responsive nature of the street,” said Margaret Crawford, a Berkeley resident and architecture professor at the university. She views San Pablo as a street with hidden charm, in part because its abundant cheap space allows weird, interesting businesses to pop up. Among them: a martial arts studio in a garage, where Crawford’s daughter took karate lessons in high school.

Others, such as Punya Karki, owner of the Himalayan Grocery in El Cerrito, fear the loss of parking may chase customers away. Karki’s store specializes in Nepalese products, serving a niche clientele who drive in from outer Costa County and other parts of the East Bay.

“It’s going to be hard if they can’t park,” he said, shaking his head.

Similar conflicts have festered for years along El Camino Real, where plans for a bus rapid transit system stumbled, as residents decried 10-mile transit-only lanes from Santa Clara to Mountain View. Housing projects have also faced resistance: Just this month, the San Bruno City Council rejected a proposal to add 425 housing units and a grocery store to the boulevard. The development would have been half a mile from Caltrain, on a street served by several bus lines.

Still, San Mateo County’s Grand Boulevard Initiative is slowly plodding along.

“We’ve finally got some multistory, multifamily residential built, which is going to lead to the type of housing-rich corridor we’d like to see,” said Belmont City Councilman Charles Stone, who also serves on boards for Caltrain and the San Mateo County Transit District. He noted that Redwood City has made bicycle and pedestrian improvements, and condominiums are popping up near the San Carlos Caltrain Station.

Mintz, the El Cerrito city planner, compared the process of revamping a corridor to a toddler’s teeth coming in: Some parts resemble smooth adult teeth, but others are crooked and gappy.

The transition might look like that for a while, said Lewis, the environmental consultant. In the Bay Area and cities throughout the country, residents and politicians are squabbling over how streets should look and function. The planners who studied San Pablo have big solutions in mind, but getting there won’t be easy.

Rachel Swan is a San Francisco Chronicle staff writer. Email: rswan@sfchronicle.com Twitter: @rachelswan