The upper deck carries the New York City Subway's IRT Broadway–Seventh Avenue Line, serving the 1 train.

By the first decade of the 20th century, the construction of the city's first subway line had made the original bridge obsolete, and a double-decker span called the 225th Street Bridge was built to accommodate the subway line above highway traffic.

[6] In 2016, the New York City Department of Transportation, which operates and maintains the bridge, reported an average daily traffic volume in both directions of 36,027.

The two central sections comprised the swing span, which pivoted around a small masonry island in the middle of the canal.

On either side of the masonry island were navigable openings that measured 104 feet 1 inch (31.72 m) wide at mean high water.

[19][26] Prior to the construction of the Harlem River Ship Canal, Marble Hill was part of Manhattan Island, and the Spuyten Duyvil Creek made a tight curve around the northern shore of Marble Hill, connecting the Hudson River on the west shore of Manhattan Island with Harlem River on the east shore.

[17][37][38] In accordance with the canal project and the congressional legislation, in 1892, the New York City Department of Public Works was commissioned to build a bridge connecting Inwood and Marble Hill, which would carry Broadway.

[41] The New York City Board of Estimate approved the Harlem Ship Canal Bridge in February 1893.

[50] The subway's West Side Branch was to cross the Harlem River Ship Canal above Broadway, which necessitated modifying or replacing the existing bridge.

[19] The need to replace the Harlem Ship Canal Bridge was further emphasized in 1903,[55][56] when the New York State Legislature passed legislation allowing the realignment of the New York Central Railroad's Spuyten Duyvil Line (now the Metro-North Railroad's Hudson Line) along the Harlem River's eastern bank.

[57] The railroad wished to avoid a grade crossing with the Metropolitan Street Railway's streetcar tracks, to be built on the lower deck.

[22][50] Ultimately, the city made an agreement with the three railroads to relocate the first span down the Harlem River, only ten years after it had been constructed.

[2] When the IRT's West Side Branch was extended in March 1906, it had a temporary terminal at 221st Street, just south of the bridge's Manhattan end.

The project was being upheld as a way to alleviate traffic on the Broadway Bridge, which in 1933 accommodated 28,000 vehicles a day, almost as much as the Holland Tunnel between New Jersey and New York.

[71] In mid-December 1934, the section of Broadway across the bridge was signed as US 9 within New York City for the first time, as were several other U.S.

[76] The 225th Street Bridge was damaged by fire that October,[76][77] requiring it to be closed for emergency repairs.

[78] In January 1957, Public Works Commissioner Frederick H. Zurmuhlen announced that the swing bridge had sustained more severe damage than originally projected, and that it would be difficult to close the swing span due to warping of the steel beams.

[13] At the end of November 1960, the second bridge was closed to vehicular traffic, but remained open for subway operation.

[82][83] Subway service on the bridge was suspended for three days starting on December 23, 1960, to install the lift span during the Christmas weekend.

[85] Subway service and pedestrian crossings resumed on December 26; the iron-grating roadbed had yet to be welded at the time.

The second swing span was towed to just north of the University Heights Bridge, where it was cut up into scrap.

[89] After further intermittent closures to marine, road, and subway traffic, work was complete by November 1963.

[90][91] The proposal failed in 1977 after the United States Congress moved to ban tolls on these bridges.

[93] The work, costing $10 million, included repairs to the deck as well as placing a protective coating on the lift span's steel beams.

[10] By 2005, the NYCDOT had classified the bridge's condition as fair, with a 3.986 rating out of 7, indicating that some components were in need of repair.

[94] In 2018, the NYCDOT awarded a contract to Tutor Perini to renovate architectural, electrical, mechanical, and structural components of the bridge.