On any given day, up to 13,000 BART workers, retirees, board directors and all their family members can ride the cash-strapped system for free, according to newly provided data from the transit agency.

Add in the the 4,000 off-duty law enforcement officers from around the Bay Area with free passes and you have more than 17,000 passes handed out by BART. That’s roughly the population of Moraga (17,416), more than double the population of Sausalito (7,125) or three times Brisbane’s population (4,693).

According to the just-released records, BART “smart card” passes have been issued to 3,624 current employees (including the transit district’s nine board members), 2,526 BART retirees, and 6,940 spouses, domestic partners and other dependents.

“Public transportation isn’t meant to operate like a profit-making enterprise,” says BART spokesman Jim Allison, who tells us it’s important for the workforce to ride the system so they have “increased exposure to the conditions our customers are experiencing.”

The employee perk has been around as long as BART, which opened its doors in 1972. Allison said the cost of running BART trains would be the same with or without the free rides, so the perk doesn’t cost the system anything.

Considering that the average round-trip BART ticket costs $7.60, the potential for new revenue comes to $130,000 a day.

This at a time when BART faces multimillion-dollar deficits and dispatches police officers to stop fare jumpers who cost the system an estimated $25 million a year.

BART officials say they’re conducting an audit of everyone who has the free-ride perk to make sure it isn’t being abused.

Dependents are automatically deactivated a month after their 19th birthday — unless they’re in school full time, in which case they can be annually renewed up to age 23. Disabled dependents keep the pass for life.

San Francisco’s Muni system gives free rides to its 6,000 employees and directors — and to police in uniform. In addition, as part of the labor contract, families of Muni’s 2,000 operators and families of retired operators also get the perk.

A spokesman for the American Public Transportation Association tells us that the practice is “very common” for transit system employees and police nationwide — and in many cases, it’s extended to spouses and dependents as well.

“If you are selling a product, you want to make sure all those associated with it know how it works and know how to improve” it, said Darnell Grisby, policy and research director at the transportation association.

BART’s Allison makes no apology for the thousands of family members and dependents who enjoy the perk.

“We are proud of our system and proud to take our families on the trains,” he said. “This has been a long-standing policy of BART, and we don’t see any reason to change that at this point.”

As we first reported last week, BART has handed out free annual passes to 4,013 police officers, district attorney’s investigators, probation officers — as well California Highway Patrol officers, state parole and Department of Justice agents, and U.S. Customs and Border Protection inspectors.

The free rides for law enforcement are conditional on the officers being certified to carry a firearm — and paying an annual $35 processing fee.

A recent BART investigation, however, found that at least 146 San Francisco probation officers who weren’t certified to carry weapons mistakenly had been issued passes as well.

Toll take: East Bay Rep. Mark DeSaulnier has been back home and getting an earful about the situation in Washington — but it was the proposed ballot measure to raise tolls on the state’s Bay Area bridges to help fund transit projects that got his blood boiling.

“This is clear example of ‘You scratch my back, and I’ll scratch yours’ politics,” said DeSaulnier, D-Concord.

The measure — which would raise tolls by $2 to $3 — is being put together by a collection of Bay Area legislators. It’s expected to generate about $125 million for a slew of road and mass transit improvements throughout the nine-county region.

“It’s all about getting money for projects in people’s districts rather than doing what really needs to be done, which is a second Bay Bridge crossing,” DeSaulnier said. “And they want the middle- and working-class people to pay for it.”

DeSaulnier is not alone. State Sen. Steve Glazer, D-Orinda, is raising questions about how the money would be spent, as is Assemblywoman Catharine Baker, R-San Ramon.

Other East Bay officials, whose constituents would pay the bulk of the toll increase, have said they’ll support the measure only if more projects are added to the goody list in Alameda and Contra Costa counties.

The measure’s author, state Sen. Jim Beall, D-San Jose, has said the measure would help ease traffic jams throughout the Bay Area. Spreading the money around, he said, is just the nature of winning voter approval.

San Francisco Chronicle columnists Phillip Matier and Andrew Ross appear Sundays, Mondays and Wednesdays. Matier can be seen on the KPIX-TV morning and evening news. He can also be heard on KCBS radio Monday through Friday at 7:50 a.m. and 5:50 p.m. Got a tip? Call (415) 777-8815, or email matierandross@sfchronicle.com. Twitter: @matierandross