Brandon Long (right) is among the many commuters using smartphones on the way to work on a Muni train stopping at San Francisco's Powell Street Station on Friday. Photo: Liz Hafalia, The Chronicle

Another rider, 24-year-old Brie Peixoto of San Francisco, said it’s clear people drift into their own world when they engage with smartphones – completely ignoring what’s happening around them, like an elderly or disabled passenger who needs a seat. She said that she tries to limit her use, but that it’s difficult.

Walking into trouble

“I try to be more aware of my surroundings, but after work, I just want to zone out,” she said.

Peixoto said she makes sure not to be on her cell phone when she’s crossing the street, another chief danger noted by San Francisco authorities. Gascón pointed to an incident in August 2011 when the driver of a Muni bus slammed into a pedestrian in a crosswalk, killing her.

The driver, whose attorney said he was lost at the time of the crash, was charged with misdemeanor vehicular manslaughter. Gascón said surveillance video showed that though the 23-year-old victim had the right-of-way, she didn’t once look up from her phone as she walked into the road.

“She never saw it coming,” he said. “Had she looked up just once, she would be alive today.”

Nasar’s 2008 study looked at the same issue, finding that almost half of all pedestrians exhibited dangerous behavior crossing the street while on their phones. They didn’t look both ways, they forced a car to stop suddenly or swerve, or they bumped into something.

Spreading awareness

Nasar later found that in 2010, more than 1,500 pedestrians were checked into emergency rooms nationwide because they were distracted by cell phones – a number that had almost tripled from 2004.

The professor is among those who hope to usher in a change in the way people use technology. Someday, with enough awareness of the dangers of distraction, he said, safe usage will be as common a practice as looking both ways while crossing the street.

“We’ve changed what is considered acceptable behavior in the United States from 30 to 40 years ago, when you would go into a meeting and everyone was smoking,” he said. “Now nobody is smoking. My hope is that something like that will happen with cell phones.”