Around Washington, surveillance cameras are always watching. They peer from rooftops, lurk at intersections and even observe people riding a bus to work.

And on Montgomery County’s Ride On buses, the cameras do more than capture what they see. Many cameras also record what they hear, a little-known function that bothers civil liberties advocates. They see a creeping erosion of privacy in the growing use of audio recording technology on public transit.

The Maryland Transit Administration began audio recording in October on some buses in and around Baltimore and hopes to expand that to about half of the agency’s 700 buses by summer.

In San Francisco, buses and trains have both audio and video recording, with the audio devices always running. And in Atlanta, transit officials are adding video and audio recording to buses and will put them on trains next.

The stated intention of the systems on the nearly 300 Ride On buses with audio recording is to capture what drivers say. But the systems, which are always recording, are capable of picking up conversations of people sitting or standing near the drivers. A passenger talking to a spouse or child could end up being recorded, the snippet saved for several days on the system’s hard drive.

Some privacy experts say audio recording devices such as those on Ride On raise serious concerns. Millions of commuters in the region board buses each year for the thousands of daily runs on the hundreds of routes snaking through the area.

George Washington University law professor Daniel J. Solove, author of “Understanding Privacy,” said recording a person during one commute might not seem particularly invasive. But with daily monitoring, “the totality of surveillance” can really add up, he said.

“Privacy is like that,” Solove said. “One camera on a bus, okay. But a camera here, a camera there, a camera everywhere, is much different.”

From body scans and pat-downs at airports to bag searches at subway stations, most Americans have come to accept less privacy while traveling since the Sept. 11 terrorist attacks ushered in a new era of transportation security.

Ubiquitous eyes

Video recording has been a part of public transit for decades and is now common on buses and trains and at stations. The 2005 terrorist attacks on the London subway were a “watershed moment” for this technology, because investigators used surveillance videos to quickly highlight images of the suspects, said Greg Hull, director of security and operations for the American Public Transportation Association, a nonprofit international industry group.

Metro has 4,400 cameras scattered through its rail system, peering at fare machines, platforms, mezzanines and other spots at all 86 stations. Each Metrobus is equipped with multiple cameras. One is a driver-specific camera that can retain video and audio, but only when triggered to do so by a crash, sudden movement or the driver pressing a button.

Known as DriveCam devices, these cameras also are used on the District’s Circulator buses, TheBus in Prince George’s County and OmniRide in Prince William County. The cameras are constantly recording, but clips are almost immediately recorded over; only when triggered does the system begin saving the recorded clips.

Arlington Transit and Fairfax Connector buses don’t have any recording devices, although officials said they could be added to their fleets.

Surveillance on transit dates to the 1970s, Hull said. It was initially used to help transit systems corroborate passenger injury claims.

Over time, large, clunky recording systems became smaller, cheaper and useful in other ways, he said. Transit agencies began using them for safety, security and employee training.

Now such recording devices are “becoming more and more commonplace,” Hull said. As older buses are replaced, agencies are looking for new vehicles to come equipped with surveillance capabilities.

Transit systems in New York City, Chicago and Philadelphia use video cameras on buses, but they do not record audio.

‘Just a part of the age’

To some commuters, surveillance is just another part of life in the 21st century.

“I feel like everything we do to a certain extent is tracked and recorded,” said Sharretta Benjamin, 32, who mostly drives but sometimes takes Metrorail and Metrobus. “It’s just part of the age we’re living in.”

Benjamin, who lives in Anacostia and works in downtown Silver Spring, said cameras are ubiquitous.

“It’s much more of a surprise to find out I’m not being recorded than to find out I am being recorded,” she said.

And Benjamin believes it’s good to have cameras on public transit because “anything can happen,” she said. She has seen people pull out weapons on buses and threaten drivers.

On Ride On, the cameras are there for the safety of both drivers and riders, said Esther Bowring, a spokeswoman for Montgomery County. The recordings are accessed only in the event of an accident or other incident, such as an attack on a driver or a complaint of driver misconduct.

“If you’re not doing anything, you have nothing to worry about,” Dantanio Stroman, 23, said while waiting for a Ride On bus in Silver Spring.

Ride On’s audio devices, which are near the driver, are recording at all times because a driver might not have time to activate it, Bowring said. “If people are having normal conversations or talking on their phones, they’re not going to be able to record that,” she said. But a the recording devices could pick up a person who is shouting or speaking loudly on the bus, Bowring said.

David Rocah, a staff attorney with the American Civil Liberties Union of Maryland, said that just because a conversation is taking place on a bus doesn’t mean “there’s no reasonable expectation of privacy.”

A lone bus rider who thinks only the driver can hear them might say something personal. And if no one else is around, that rider should be able to expect privacy, Rocah said.

The law treats audio and video recording differently, and people act accordingly, Rocah said. The different treatment stems from a common belief that there can be “more at stake in terms of what we say than what we do in public,” he said.

As a result, people often have “very private conversations” in public if they think no one can hear them, he said.

Stickers are posted on Ride On buses to alert riders about the recording devices on board. But having such a sticker or sign doesn’t mean a rider automatically forfeits privacy, in part because many riders have no choice but to use public transit, Rocah said.

A system that records only during incidents “would not raise any concerns” from a privacy perspective, he said.

Such incidents, sometimes very serious, do occur. In 2008, 14-year-old Tai Lam was shot and killed on a Ride On bus in Silver Spring.

The driver activated a silent alarm to alert authorities. At the time, nearly 60 percent of Ride On’s buses had cameras, but that bus didn’t. The county now has cameras on most of its 339 buses, and as older buses are phased out, the plan is for new buses to come with cameras.

Alex Love, a friend of Lam’s, said cameras on buses are necessary because “you never know” what can happen.

“It keeps people on the right track,” Love, 19, of College Park said while waiting for a Ride On bus in Silver Spring. “If you know you’re being watched, there’s less of a chance of you doing the wrong thing.”