Determining the “busiest” NYC subway line depends on the metric used (ridership, trains per hour, crowding, etc.), but based on the most common measure — annual ridership — the frontrunners are:

1. By Total Annual Ridership (Pre-Pandemic & Recent)

Historically and currently, the Lexington Avenue Line (4/5/6 trains) is the busiest trunk line in the system. It serves the East Side of Manhattan, a major job center, and connects with numerous transfer points.

• 4/5/6 trains together carried ~1.3 million riders on a typical weekday before COVID-19.
• Even post-pandemic, it remains the busiest, with the 6 train often being the single most crowded route.

2. By Peak Crowding & Trains Per Hour

The Flushing Line (7 train) often claims the title for highest peak crowding and most frequent service (with up to 30 trains per hour during rush hour pre-pandemic). It serves dense residential areas in Queens and connects to Grand Central.

3. Other Notable Busy Lines

• 8th Avenue Line (A/C/E): The A train is one of the longest and busiest routes, especially in Brooklyn and Upper Manhattan.
• Broadway Line (N/Q/R/W): Heavily used in Manhattan and Brooklyn.
• 14th Street-Canarsie Line (L train): Extremely crowded before service reductions in 2019–2020; still busy.

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Key Factors Influencing Busyness

• Manhattan trunk lines