After six months, 1.2 million people had visited the NMAAHC, making it one of the four most-visited Smithsonian museums. Patrons spent an average of six hours at the museum; twice as long as had been estimated before the museum's opening. The museum's popularity led to some problems. Visitors stood in line in the museum foyer to take an elevator down to the underground level. The exhibits start with the Middle Passage and slavery where the hallway is intentionally designed to be cramped and somewhat claustrophobic. The large number of visitors who stop to read the exhibit's signs caused dangerous overcrowding. Museum officials began to limit the number of people who could take the elevator (and thus enter the exhibit) to mitigate this problem, although this led to still longer lines in the foyer.