Bottleneck and Over-crowding

Bottleneck noun - A crowded mass (as of cars) that impedes or blocks movement.

Over-crowding and bottleneck are semantically related In some cases you can replace phrase "Over-crowding" with "Bottleneck", this terms are similar.

Over-crowding noun - Excessive crowding.

Bottleneck and over-crowding are semantically related in blockage topic. Sometimes you can use "Bottleneck" instead a noun phrase "Over-crowding".