But in January, Governor Cuomo, who controls the authority, essentially took over the project and announced a last-minute rescue plan that relied on a part-time construction schedule, with work affecting only one of the tunnel’s two tubes at a time.

That limits the work to nights and weekends, when service is reduced to every 20 minutes.

Work began Friday night. There were large crowds and some annoyance and confusion among riders over the weekend, but nothing apocalyptic.

The main challenge on Monday morning for the agency and the subway chief, Andy Byford, was to make sure workers would finish up overnight construction and remove themselves and their equipment in time for rush hour.

We go now to Emma:

So I take it the workers finished up in time for rush hour?

Yes, they have to get the workers and the equipment out to restart rush-hour service, and that’s going to continue to be a challenge.

If rush hour had started with only one tube open, it would have been a real disaster. But there were no major incidents, no trains stuck in tunnels, no catastrophes.

There was some overcrowding over the weekend?

Yes, there were lines just to go down the stairs onto the train platform, almost like the bouncer line at a nightclub.

But over all, far better than a full shutdown?

If you miss your train, you have to stand on the platform for at least 20 minutes. But as the governor’s office is saying, this is better than full closure, with no trains running at all.