The most crowded train in the NYC Subway system is often considered to be the 4, 5, and 6 trains during peak hours. These lines, collectively known as the Lexington Avenue Line, serve a significant portion of Manhattan and the Bronx, and experience high ridership due to several reasons: 1.

That’s a great question, but it’s surprisingly difficult to answer definitively because the New York City subway system is measured in several ways: by ridership, by length, by number of stations, and by cultural fame.

However, if we go by the single most important metric—annual ridership—the crown goes to:

The Lexington Avenue Line (served by the 4, 5, 6, and <6> trains)

Here’s why it’s considered the most popular/busiest:

• Sheer Volume: It carries more passengers than any other line in the United States. Pre-pandemic, the 4, 5, and 6 trains together served over 1.3 million riders on an average weekday.
• Critical Route: It runs under Manhattan’s East Side, connecting major hubs like:
  • Grand Central Terminal
  • Wall Street (via the 4 and 5)
  • The Upper East Side
  • Brooklyn Bridge-City Hall
  • Key Bronx neighborhoods
• No Parallel Service: For much of its route in Manhattan, there is no direct east-side alternative, funneling all east-side commuters onto this one trunk line.

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Other Strong Contenders by Different Metrics:

1. The Flushing Line (7 train): Often cited as the second busiest. It’s famous for being the “International Express,” running through incredibly diverse neighborhoods in Queens and terminating at Times Square. It was the first to get modern, high-tech trains.

2. The 8th Avenue Line (A, C, E trains): The longest line