How much would you pay to park at your local BART station if you knew you could count on getting a spot?

Or, if you had the choice, how much would that spot have to cost before you’d give it up and walk, carpool or take a bus to the station instead?

Those are some of the questions that could determine how much patrons pay to park at BART in the future, as the transit agency that once surrounded its stations with vast lots of free spaces considers price hikes for a shrinking inventory of spots.

The $3 fee BART charges for all-day parking at many stations could double at some of the system’s most popular lots and garages — or rise by even more — under ideas the agency’s board will discuss at the annual retreat this week that serves as a preview of its priorities for the year.

Opponents, as well as many passengers who park and ride, resist the idea of paying more, warning it could lead more people to ditch BART and worsen the area’s grinding rush-hour traffic.

“I would probably drive a little more,” said Lisa Winn, a meeting planner who lives in Danville and commutes to work by driving to the Walnut Creek BART station, then riding to work in Oakland. With free parking available at her job, Winn said, she might join the traffic on Highway 24 if BART’s lots were too pricey.

“There is a tipping point,” she said.

But supporters argue that BART parking suffers from a rare problem in today’s Bay Area: It’s too cheap.

By capping weekday parking fees for all but one lot at $3, there is little incentive for riders not to drive if they have another option — parking at BART is barely more expensive, for instance, than a bus fare. The exception is the West Oakland station, which is one stop away from San Francisco and has parking fees that run $10.50 per day.

The result is packed lots that fill up well before rush-hour at some stations and wait lists tens of thousands of people long for the coveted monthly parking permits that guarantee a space.

Across the entire system, 29 percent of BART’s weekday riders drove or carpooled to their stop in 2015, according to the most recent data that is available. That share is higher in more car-dependent suburbs. More than half of those commuters drove or carpooled to the Dublin/Pleasanton and Orinda stations, where the lots typically fill well before 8 a.m.

“We clearly are not charging enough to have a big impact on demand,” said BART director Rebecca Saltzman, who said she wants to see a more “demand-based” parking rate.

Charge more for spots, the thinking goes, and the people who have another way to get to BART would use it. That would in theory free up a space for some other rider who really needs it — say, a parent who lives far from the nearest station and has to drop off kids before catching the train and can’t show up before 8 a.m. to secure a spot.

“We could be charging more and opening up some spaces for people who don’t have another choice,” Saltzman said.

Another Walnut Creek rider, Linda Fisher, didn’t like the idea of pricier parking, noting that it comes as BART is also raising fares. But she may be an unwitting poster child for the concept.

Fisher lives less than a mile from the station, saying she drives because it saves her time. She wouldn’t dream of driving to her banking-industry job in downtown San Francisco, with its traffic and astronomical parking costs.

“Even if they increased it $1 a day, that would be too much” to justify parking at the station, Fisher said. So she’d likely walk to BART or work from home more — freeing up a space in the lot.

Still others at the station said they would keep driving to BART, even if it meant paying more.

“What other options are there?” said Albert Hahn, an accountant who drives to BART because bus service between the station and his home in Alamo is too slow.

Parking spaces are likely to become more scarce as BART swaps some stations’ sprawling surface lots for new apartment buildings under a push to build 20,000 units of housing on the agency’s property. BART officials stress that they consider each station’s parking needs when deciding how many spaces to replace when a new development goes up, but many car-dependent commuters are wary.

At Thursday’s board retreat, agency officials will lay out a couple of scenarios for raising parking rates, though the board won’t vote on any of them.

One option includes raising the cap on daily parking fees from $3 to $6. There could be similar price increases for single-day and monthly permits and a range of prices based on demand at each station. Drivers might pay $6 to park at the Dublin/Pleasanton station, for instance, but perhaps $2 at North Concord/Martinez, which never fills up. BART estimates such an increase could bring in $10 million to $15 million in new revenue.

Or the agency could eliminate the cap entirely, replacing it with a system that allowed for increases every six months with no final limit on how high the price could go. BART forecasts an additional $12 million to $17 million annually from that model.

Board members also will consider ideas to lower parking rates when demand is lower, such as on Fridays or during holiday weeks, when lots are less likely to fill. There is no indication the system will start charging for parking during evenings or on weekends, when BART’s ridership is way down.

BART spokeswoman Alicia Trost stressed those ideas are not specific proposals but rather “examples to get the discussion going.” BART staff are now studying what impact higher parking costs could have on low-income riders, a first step toward potentially making those increases a reality.

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Editorial: Electing Allen and Wallace crucial for BART’s solvency And any price hike proposal is far from guaranteed — it would require approval from two-thirds of the BART board, which could be a high bar considering several directors come from suburbs where riders see few options but their cars for getting to stations.

“Every time you raise fares, every time you raise parking costs, it becomes less affordable,” said Director Debora Allen, who represents four central Contra Costa County stations. Allen added that she would oppose raising parking rates any more than overall cost-of-living increases.

“Let’s talk about how we’re going to bring riders back — we are not going to do that by raising parking fees and reducing parking,” she said.