Muni is beefing up security at a time when crime is plummeting on the San Francisco transit system — a stark contrast to its regional neighbor, BART.

Still under pressure to improve, the San Francisco Municipal Transportation Agency tapped a veteran of the Baltimore Police Department to be the next chief security officer of the bus and train system. At the same time, the Board of Directors is weighing a $60 million, three-year security contract that would increase the number of unarmed and armed guards patrolling bus yards, major platforms and ticket vending kiosks. The plan would increase Muni’s security spending by about 30%.

“We’re adding extra bodies at facilities so operators feel safer, which is great for (employee) retention,” said transportation agency spokeswoman Erica Kato. “We’ll also increase security on platforms and at subway stations.”

These safety measures would build on several years of progress. Crime has dropped dramatically on Muni, from 2,236 “security incidents” in 2014 to 1,145 last year and 461 through June this year. The category covers a broad range of unruly behavior, including burglary, assault, arson, graffiti or vandalism, rape, theft, robbery, burglary or mental health issues.

The trend distinguishes San Francisco’s always-packed buses and trains from the more suburban BART system, where violent crime doubled in the last four years. Unlike BART, Muni doesn’t have its own police force. Instead, the agency contracts with San Francisco police officers who patrol the transit system during commute hours.

For years Muni has invested in alternatives to law enforcement, such as civilian security guards and surveillance cameras. Its subway stations have sturdy fare gates with tall rubber panels to deter cheats — a model that BART seeks to emulate when it replaces its fare gates.

“I will say frankly that I never feel afraid on Muni, and I ride it at all times of the day,” said Cat Carter, interim executive director of the grassroots group San Francisco Transit Riders. “The worst I see is ... unstable people moving erratically with, say, a container of yogurt in their hands that may splatter everywhere. But that’s not an assault.”

Nobody can quite explain what’s caused Muni’s dip in crime, though many have theories. Some say the city’s transportation agency has a more effective security strategy than its regional counterpart. Others, including BART Board President Bevan Dufty, wonder whether Muni’s heavy crowds intimidate and discourage would-be perpetrators: much of the violence and disorder on BART — including a recent fatal stabbing — occurs during non-commute hours.

One problem at Muni has been slower to change. The agency still contends with persistent attacks on its drivers, who complain that riders spit on them, make death threats, or throw items — in one particularly harrowing example, a man tossed a cup of vomit into a female driver’s face. Crimes against drivers are included in the system-wide statistics, and they are also waning, but at a slower rate than crimes overall.

“We’ve had a number of challenges trying to ensure safety and security for all patrons,” said the agency’s interim chief security officer Glenn Mar. He noted that Muni, like BART, is grappling with a regional homelessness crisis that spills into the transit system. Transients periodically wander into the subway tunnels in search of a place to camp out, causing system-wide delays.

Yet if homelessness and “quality of life” issues create an inconvenience for passengers, they haven’t brought serious crime. Muni has worked with San Francisco’s Homeless Outreach Team to divert some transient riders into shelters, while expanding a Transit Assistance Program that trains community members to de-escalate conflicts on Muni school routes.

The agency still wrestles with a widespread perception that it’s unsafe, abetted by social media videos documenting bad behavior on Muni.

New chief security officer Kimberly Burrus said she’ll try to fix that when she starts work Monday.

“I believe Muni and I are at the same crossroads at the same time, when all the good you could have accomplished is tarnished by a bump in the road,” she said.

She started her career as a patrol officer in Baltimore and rose up the ranks to become a commander, before she was investigated for allegedly misspending charity funds on vacation tickets. Burrus’ ex-husband, a police captain, made the allegations during a testy divorce proceeding in 2017. She said they were false, and the Baltimore state attorney’s office declined to file criminal charges. Still, she was demoted to lieutenant and resigned earlier this year, after suing the department for violating her right to due process. The suit is pending.

Top officials at Muni said they support Burrus and “look forward to the leadership and expertise she will bring to the agency.”

In a statement, the agency described Burrus as “incredibly brave, transparent, and open in sharing the details of her past experiences in Baltimore.” It went on to praise her extensive law enforcement experience as a “valued asset.”

Baltimore’s regional rail and bus lines confront many of the same social issues as BART and Muni, including violent assaults, Burrus said. Yet San Francisco stands out for the number of attacks on transit employees, who may be more vulnerable than riders. Verbal and physical altercations involving operators have decreased, from 575 in 2017 to 522 last year, but that’s still more than one a day.

Many of these incidents occur at the end of a line, when operators have to clear out stragglers, said Roger Marenco, president of San Francisco’s Transport Workers’ Union.

“That’s when it can get very contentious and dangerous,” Marenco said.

Passengers riding Muni buses and trains on Wednesday said they see very little crime on the system, though they don’t necessarily believe it’s declining.

“I think it depends on what line you ride,” Chandra Walker said as she boarded the F-Market streetcar Wednesday morning.

“Maybe it’s the police presence,” said Mads Leigh, an Oakland resident who was exiting Muni at the Powell Street Station. Leigh said he sees what he considers to be ample police on all Bay Area transit systems, and he worries they may be harassing people for minor offenses.

Canadian public transportation researcher Todd Litman said big swings in crime statistics are common on transit systems, because the overall number of crimes is so low, considering how many people ride them. Roughly 720,000 people ride Muni every weekday, so every passenger had a very small chance of being the victim of a crime last year.

“When you have such statistically small numbers, you get huge year-to-year variations,” Littman said. “It may just be totally random.”

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