The Metropolitan Transit System has figured out how much it could raise through a new sales tax, and now it’s polling voters to gauge the popularity of the measure and specific transit projects.

The measure, which could appear on the 2020 ballot, is becoming a priority for local leaders, as individual cities and the region as a whole have pledged to break San Diego’s reliance on cars, both to cut carbon emissions and to alleviate a housing shortage through dense, transit-focused development. But the measure would also remake MTS’s role in the region, putting it in charge of a major capital program that has in recent decades been the San Diego Association of Governments’ responsibility.

An MTS-commissioned forecast, obtained through a public records request, found the agency could bring in roughly $5.3 billion over 20 years, or $13.2 billion over 40 years, through a half-percent sales tax.

The agency would stretch that revenue by using it to compete for state and federal dollars to cover the costs of major transportation projects. In the past, the San Diego Association of Governments has assumed it could bring in $1 from outside San Diego for every $1 it collects locally.

“It’s definitely enough,” said MTS Chair Georgette Gomez, one of seven board members on an ad hoc committee in charge of building the measure. “It’s significant. My reaction is that this is real money, especially because it can be leveraged.”

Besides Gomez, the committee also includes council members Chris Ward from San Diego, Mona Rios from National City, Paloma Aguirre from Imperial Beach, David Arambula from Lemon Grove and Bill Sandke from Coronado, along with Supervisor Nathan Fletcher from the county. The next meeting is on Feb. 21, though meetings are not open to the public.

MTS staffers and consultants are currently building a list of potential projects with ridership projections that could be included in a measure. And the agency intends to form a “citizen’s advisory committee” with representatives from labor, transit, environmental and social justice groups, and other interest groups.

Rob Schupp, an MTS spokesman, said that group would help select projects and establish priorities, and that the bottom-up approach is intended to avoid mistakes that SANDAG made with its 2016 transportation measure, which faced opposition from both the left and the right through Election Day.

“One mistake SANDAG made is it wasn’t inclusive enough early enough,” he said.

La Mesa Councilman Colin Parent, who also runs the transportation advocacy Circulate San Diego that will soon release a report on its vision for an MTS measure, argued the measure needs to not only focus on projects that poll well, but on provisions that win support from active and powerful political constituencies. That could mean including a project that connects the trolley to the airport to entice hoteliers, and promises to organized labor for construction jobs.

“One thing that didn’t happen in 2016 is, there wasn’t a sufficient effort to get buy-in,” he said. “MTS is trying to do a more open public process, and that’s good, but it’s also necessary.”

But the measure would represent a departure for MTS, which has until now focused on operating a transit system largely built by SANDAG.

For that reason, Schupp said the agency would consider a smaller measure that props up the current system by subsidizing fares and increasing frequencies, in part because it’s too early to take anything off the table.

That is not Gomez’s vision. She does not want a narrow measure.

“MTS is more than capable of taking this on,” Gomez said. “One of the things I’ve realized is that there is a disconnect when the transit agency isn’t driving the conversation, other agencies are, and then MTS has to fit in the box they create.”

Ward said he’s focused on building a transit system that will support all the increased development that city leaders have in mind. The City Council and mayor are increasingly on board with slashing development regulations near transit stations – called transit priority areas – to both combat the region’s housing shortage and to cut our greenhouse footprint by making it easier to commute without a car.

“We want to align development along transit priority areas and that’s all well and good, but you need something on the other side of the equation,” he said. “The backbones are there, and that’s what we’re designing around, but you have to have the system that will make transit a positive choice.” Likewise, Gomez points to ambitious goals like the city’s aim of getting half of residents who live near major transit stations to commute by biking, walking or taking transit by 2035, and similar climate action plans adopted by other cities, and says they aren’t realistic without major changes to the transit system.

“Some of us are saying that we want a system that’s competitive with driving, but that requires money behind it,” she said. “These (climate action plans), achieving them in totality requires shifting modes of transportation. I’m interested in creating choices and letting people’s behavior change.”

One political boon to the measure came in AB 805, the state law that gave MTS the ability to collect its own taxes. That measure also said it could build so-called complete streets on whichever corridors its transit lines operate.

That means the measure could include road repairs as long as it also includes building protected bike lanes, sidewalk enhancements or dedicated bus lanes.

“That’s important, because pothole repair typically polls better than transit,” Parent said. “You want to be able to credibly say, ‘OK drivers, we’ll repair your potholes, but only on streets that other people get to use too.’”