noun, noun or participle which takes 'suru', intransitive verb
congestion; crowding; jam
The common modern meaning: a place, vehicle, road, line, or system is crowded or congested. As 混雑する, it is intransitive: 電車が混雑する, not 電車を混雑する.
朝の電車はいつも混雑している。
The morning trains are always crowded.
連休中は
Highway congestion is expected during the long weekend.
noun, noun or participle which takes 'suru', intransitive verb
confusion; disorder; chaotic congestion
A broader or less common use for a confused, disorderly state where many things are mixed together. In everyday Japanese, 混乱 is often clearer for pure 'confusion'; 混雑 here often still suggests a crowded or tangled situation.
事故直後、現場は混雑を極め、指示がなかなか伝わらなかった。
Immediately after the accident, the scene was in extreme disorder, and instructions did not get through easily.