With a few steps, Xavier Lacombe, 6, buzzed through 100 years of subway car technology at the New York Transit Museum on a recent afternoon. Nathaniel Lacombe, 2, followed behind his older brother’s dizzying path: R-30, to an R-11 prototype, parking themselves on the faux-rattan seats of an ancient AB Standard.

“This looks just like the real subway,” Xavier paused, “because it is the real subway!”

In the decommissioned Court Street Station in Boerum Hill, Brooklyn, the Transit Museum opened as a temporary exhibit on July 4, 1976, in celebration of the country’s bicentennial. Transit Authority staff conceived the idea as a way to remind New Yorkers of the system’s technological innovation during a period when the subway was covered in graffiti and plagued by crime.

The exhibit was supposed to run through the summer, until Labor Day. But the staffers underestimated New Yorker’s fascination with how they move around the city.

“It was so popular after the summer that, here we are 40 years later, still open,” said Regina Asborno, the museum’s acting director. Now the museum serves 500,000 visitors annually at its locations, including below-ground headquarters and in its Grand Central Terminal exhibit.

Asborno and staff will begin celebrating its 40th anniversary, a surprise success story, with the public this weekend. Festivities will kick off Sunday morning with a breakfast, crafts, dancing and vintage subway and bus rides. In the afternoon, there will be a block party on Schermerhorn Street and free admission to the museum.

“The whole idea of being down here is an exploration of looking at what you see every day in a new light,” said Asborno, as she sat in her favorite vintage subway car in the museum’s collection: the R-11, the prototype originally built in 1949 for the still unopened Second Avenue Subway. The car, featuring a stainless- steel frame, porthole and a painted teal interior, was the pinnacle of sleek for its day.

”This was what the future was supposed to look like in 1949,” she said. “That tealy-blue color of the 1950s. I know this car has been used in a couple of film shoots. It’s definitely all about the color. I’ve heard the directors saying, ‘That’s the color’ and I’d say, ‘Well, actually, historically this would be the train that would be more often seen. And they’d say, ‘No, no. That’s the color.’”

The museum, a self-supporting division of the MTA, focuses on issues of the day, like rebuilding after Superstorm Sandy, but also historical minutiae.

There’s a display of old subway slugs from the MTA’s token era. One coin features an etching of an outstretched hand with the surrounding text, “give nothing, get nothing.”