– Life can change in a second. Marca Bristo knows that.

Her second happened in 1977. The then-23-year-old world traveler and career woman inhaled deeply as she watched the waves on Lake Michigan. Next, she dove headfirst into the blue water and into life with a disability.

“Zap,” she said. The plunge broke her neck and paralyzed her from the chest down.

“I lost my home, my health insurance, my means of getting around the city,” she said. “One day I was one way, and the next day I was different.”

Different meant living life seated. But it also meant realizing that her wheelchair did not limit her — the city around her did. “A wheelchair is a liberation device,” Bristo said, but “1977 Chicago was sort of like a Third World country.”

It was before the Americans with Disabilities Act, which was signed into law 25 years ago Sunday. Buses didn’t kneel for wheelchairs and curbs weren’t cut into ramps.

That grocery store a block and a half from Bristo’s house? Impossible to get to. And if she wanted to go out for dinner, front steps were impassable mountains, and front doors were rarely wide enough.

But the federal act changed that, said Bristo, now president and CEO of Chicago’s Access Living, which engages the city’s disabled community.

“We just had Independence Day, July 4. But July 26 is our Independence Day,” she said. “It was a moment where we ourselves felt strong. It was just jubilation. Nothing short of that. Aside from being a legal victory, it also represented a huge philosophic shift.”

Over the course of 25 years, Chicago has changed into a city that the disabled can navigate. Whether physically disabled, blind, deaf, unable to speak or mentally disabled, a grocery store trip or run to the bank isn’t out of the question. Neither is visiting family or friends, commuting to work or attending a baseball game.

Every fixed-route bus is now accessible to disabled people, said Susan Massel, spokeswoman for the Regional Transportation Authority. One hundred train stations are accessible too, and both trains and buses — and more than 330 bus shelters — have automated audio and visual route identification and stop announcements.

“I think it’s wonderful,” said Terri Michaels, 57. Because of the act, her 22-year-old intellectually disabled daughter, Annie Michaels, works three jobs and takes public transportation to all of them.

Though fixed-route transportation is free for some disabled, Massel said $3 prearranged shuttles rides can pick them up and deliver them to exact locations. That’s how Renita Freeman, 62, gets to her doctor’s appointments.

Freeman lived most of her life on her feet, but after carpal tunnel syndrome, a diabetes diagnosis and osteoporosis, “my body just broke down.” She avoided the inevitable as long as she could.

“I let the wheelchair sit in my house for like three years, four years,” she said. Instead, she used a cane. Then a walker. “I was terrified. You worry about the people, what they’re going to say.” But one day she sat down anyway. And rolled forward in that wheelchair.

She explores her block, her neighborhood. She boards buses to work, where she helps teach young children at Holman Leadership Academy. She visits friends.

The transportation system “could use some more bells and whistles, but it gets us around,” she said. “Whoever thought of the disabilities act, I applaud that person.”

While many will celebrate Sunday’s ADA anniversary, the Chicago initiative will acknowledge its shortfalls, said Karen Tamley, commissioner of the Mayor’s Office for People with Disabilities. Some ideas? Expand the number of accessible taxicabs, fitness centers and playgrounds.

The gap in disabled employment rates has not budged much since the act passed. Disability-friendly design is still an afterthought, not a planned priority, she said. “The promise of the ADA is not yet complete,” she said. “There’s still a lot of work to be done.”