For more than half a century, it has stood out as a singularly vexing flaw of the subway system, a glaring inequity that has frustrated generations of riders and has even puzzled transit officials, who have wondered how the situation ever came to be.

But beginning on Tuesday, once the first travelers make their way between a B train and an uptown No. 6 at Bleecker Street, a daily frustration will have given way to a whimsical remembrance: Here stood New York City’s fussiest subway transfer point, the one that went one way but not the other.

Until this week, only riders on downtown No. 6 trains at Bleecker Street could transfer to the B, D, F or M lines at Broadway-Lafayette. Riders from the other direction would have to switch trains elsewhere — at Jay Street-Borough Hall or Atlantic Avenue-Pacific Street in Brooklyn, for example — or suffer the inconvenience of a walk above ground between the Broadway-Lafayette and Bleecker Street stations, capped by an extra MetroCard swipe.

But with the completion of a construction project of the Metropolitan Transportation Authority that included a platform extension and the installation of new elevators, the system’s only such incomplete transfer point has been made whole. “It’s the last kink,” said Peter Tashjian, 41, a No. 6 rider from the Upper East Side. “It’s like you’re smoothing out the wallpaper and the last little bubble is pressed out.”