Michael Kirby Smith, 31, is a New York-based freelance photographer. Since late in March, Mr. Smith, who grew up in Dallas, has been exploring the notion of barriers in New York — their role in the city’s past and present, as well as the human interactions they inspire.

Over the course of the project, Mr. Smith struggled to gain access to bodegas and liquor shops. In some cases, he only had 10 minutes to shoot. But he persisted. He was intrigued by the idea that the project could reveal something about the New York of yesteryear, “a grittiness that used to be more apparent,” he said. “It still exists, but it’s not apparent like it once was in a Bruce Davidson photograph in the ’80s on the subway. It’s more on the peripheral.”

Mr. Smith’s photo essay will be published in Sunday’s Metropolitan section.

In some New York neighborhoods, business after dark still takes on an altogether noirish hue, even though citywide violent crime has fallen by nearly 30 percent over the last decade. At night, the handshakes and fist-bumps are gone — the cheerful banter between friendly clerks and customers replaced by strained conversations conducted through Plexiglas. For store owners and overnight clerks, transaction windows in varying styles and degrees of security are an essential safeguard; for customers in still-dangerous neighborhoods, they are a way of life, a grim reminder that progress takes time.

“It’s just everywhere,” Charlie Colon, the owner of two Harlem pawn shops, said of the city’s transaction windows, as the evening sky over Frederick Douglass Boulevard turned a steely gray. “I almost compare it to the taxicabs; if you have one they can’t get to you; if you don’t have one you get gotten.”

But even businesses that deal less in cash and jewelry sport bulky shields, barriers through which vendors pass fried fish sandwiches, or even the incongruously innocent ice cream cone.

Customers like Jerry Evans, who emerged from a Harlem RiteCheck outlet on Adam Clayton Powell Boulevard at West 145th Street, with a wad of cash in hand, said such windows are a nuisance — and potentially dangerous. They slow down each sale, he said, exposing money-wielding customers to outside onlookers like sitting ducks.

“You’re definitely gonna have trouble hearing,” Mr. Evans, 45, added. “And you gotta say it at least two or three times” before the clerk understands your order.

As a result, some clerks, cognizant of the stigma associated with transaction windows, are keeping them open — even well into the night — creating what Shaquan Bey calls a more “customer-friendly” experience.

The O’fishole Seafood stand, on West 145th Street, between Frederick Douglass and Adam Clayton Powell Boulevards, where Mr. Bey works the counter and the kitchen, recently replaced its higher-security Lazy-Susan-style transaction window with a sliding one decorated with handwritten signs advertising $1 lemonade and a raffle.

“We’re just trying to spruce it up,” Mr. Bey, 33, said, “make our business a little bit different.”