BART has lost nearly 10 million night and weekend passengers in just four years at a time when the region is enthusiastically promoting a transit first philosophy.

Data from the four-county rail system shows the disconnect between Bay Area transportation habits and purported Bay Area values. Though trains continue to fill during rush hour, fewer people are riding BART to museums, parks or shopping centers.

Outside the peak commute times, ridership plummeted — from 62.2 million in 2015 to 52.7 million last year.

“On Saturdays and Sundays, BART feels deserted,” said Lateefah Simon, president of the transit agency’s board of directors. To her, the numbers merely confirm what any regular rider can see.

A recent BART survey of 662 commuters in five counties may help explain the evening and weekend drops in ridership. Nearly a third — 29% — of respondents said they take BART less often on weekends than they did a year ago. The primary reasons: They’re not traveling to places served by the rail system, and weekend rail service is too sparse.

Yet they also cited misgivings about crime, filth and homeless people seeking shelter on the rail system, which, according to the survey, were a bigger deterrent than service delays, the cost of fares or disruptions from weekend track repair.

The transit agency’s board will discuss these results Thursday during its annual two-day workshop, a time to take stock of the system and plan improvements for the coming year. Officials at BART hope to accelerate the rollout of the system’s new train fleet, which so far has been hobbled by mechanical issues. They may run more new Fleet of the Future trains on Saturdays while offering special event fare discounts to lure back weekend riders.

“I have pushed my staff quite aggressively to come up with some incentives for weekend ridership,” said General Manager Bob Powers, who is pressing for consistent train schedules and considering various promotions. Among them: half-price fares for families of four, or day passes for $8.

These ideas appeal to Director Janice Li, who understands why people would be disenchanted with Saturday and Sunday service. Even she tries to avoid BART on Sundays.

“It’s just the lack of reliability, and how long you have to wait,” Li said. “We all know that feeling of running down the escalator to catch a train and then watching it pull away. And then you look at the next arrival time and it’s 25 minutes.”

Rider surveys provide useful guidance for BART, agency spokeswoman Alicia Trost said, noting changes the transit agency made after its customer approval ratings tanked last year.

BART now partners with San Francisco, Alameda and Contra Costa counties to pay for homeless outreach teams in its trains and stations. Separately, the agency hired an internationally decorated “master cleaner” to train its custodial staff.

But it may take more creative solutions to entice people into the empty weekend trains.

“What’s going to get my mom on a train? Half-priced Sundays,” said Simon.

She’s consistently pressed for discount fares, noting that BART faces stiff competition from ride-hailing services, which might be a cheaper option for some travelers.

The ridership slump at BART also illustrates a national trend. Rail travel rose by 5% throughout the country from 2012 to 2014. But by 2018, those gains had evaporated, according to the American Public Transportation Association.

During that same period, fares climbed by an average of 13% on large transit systems while gas prices fell 29%, making it cheaper to drive in many instances.

While subway officials throughout the country struggle to stem the loss of passengers, BART has focused investments on the social issues that disturb riders the most. When the rush hour crowds subside, trains become a refuge for people with nowhere else to go: From January to March of last year, officials counted 292 transients for every 100 train cars on weekends — up from 125 in 2018.

In many ways, the agency now plays a second role as a social service provider. Over the past seven years, BART has spent more than $59 million and hired 93 full-time employees to tackle quality-of-life concerns — a broad category that includes everything from security gates to homeless outreach teams.

Most recently, BART dispatched 10 uniformed ambassadors to keep order on the trains each day. They will work from 2 p.m. to midnight on weekdays, with extra patrols on Saturdays.

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