It was easy to imagine the blue bikes in fair weather, spinning over the East River during the morning commute, or toward the sidewalk cafes of SoHo for a twilight meal.

Yet as Citi Bike, the bike-share program in New York, quickly evolved from curiosity to lifeline to verb, even supporters acknowledged that a reckoning would arrive as the calendar turned to winter.

The city’s program, unlike those of some cold-weather counterparts, remains open all year. And in the throes of an especially unforgiving winter, the system is confronting perhaps its greatest test yet: negotiating the expected nose dive in ridership, scrambling to protect its stock from storms and showing that a program powered in large measure by novice cyclists can endure a season of black ice and face-whipping wind.

What has emerged is something of an urban survival sport, the ranks thinning but never disappearing as the temperature dips.