What is "bottlenecks"

Usage examples of "bottlenecks".

Unnerving, because Hel was now totally dependent on the cable, after ninety minutes of negotiating the narrow, twisting shaft with its bottlenecks, narrow ledges, tricky dihedrons, and tight passages down which he had to ease himself gingerly, never surrendering to gravity because the cable was slack to give him maneuvering freedom.

Street barricades were already going up here and there, causing unfortunate bottlenecks of desperate people.