to be crowded; to go into; to put into (suffix representing deepness / completion)
朝の通勤ラッシュ時の新幹線や地下鉄は、乗客で非常に_______ため、毎日の移動だけで体力を著しく消耗します。
Because Shinkansen and subways during the morning commuting rush are extremely crowded with passengers, physical strength is remarkably consumed just by daily movement.