The Park Avenue main line, which consists of the Park Avenue Tunnel and the Park Avenue Viaduct, is a railroad line in the New York City borough of Manhattan, running entirely along Park Avenue. The line carries four tracks of the Metro-North Railroad as a tunnel from Grand Central Terminal at 42nd Street to a portal at 97th Street, where it rises to a viaduct north of 99th Street and continues over the Harlem River into the Bronx over the Park Avenue Bridge. During rush hours, Metro-North uses three of the four tracks in the peak direction.

Park Avenue is a boulevard in New York City that carries north and southbound traffic in the boroughs of Manhattan and the Bronx. For most of the road's length in Manhattan, it runs parallel to Madison Avenue to the west and Lexington Avenue to the east. Park Avenue's entire length was formerly called Fourth Avenue; the title still applies to the section between Cooper Square and 14th Street. The avenue is called Union Square East between 14th and 17th Streets, and Park Avenue South between 17th and 32nd Streets.