Manhattan’s High Line, an elevated green trail repurposed from an old rail spur on the west side of Manhattan, grew a little bigger this June with the completion of a 600-foot span that incorporates two footbridges, one made of mass timber trusses, making for an unusual site over the busy streets of Midtown West.
“We used Alaskan yellow cedar to create a Warren truss — a nod to the historic industrial character of Chelsea, reminiscent of the steel rail bridges of that era,” says design principal Kim Van Holsbeke, of SOM, architect for the project.
The design objective was to create a “contemporary version” that references the “industrial legacy” of the Chelsea neighborhood and the many historic Warren truss configurations of old bridges throughout the country, he says.
The new High Line addition, known as the Moynihan Connector, creates a continuous path from the High Line to the Moynihan Train Hall. The High Line stretches above Manhattan streets for about 2.5 miles.
The first time mass timber has been used on the High Line, the cross-laminated timber bridge is configured in three 65-foot-long sections supported by two metal columns and the Woodland Bridge. The timber crossing cantilevers outward by 65 feet to reach the Magnolia Court at Manhattan West, says the architect.
SOM specified mass timber not just because of its fit with the neighborhood’s history.
“Mass timber is a regenerative, low-carbon material, and minimizing carbon emissions is one of the main goals in all our work,” explains Van Holsbeke.
Timber, he adds is “complementary” to the landscaping on Moynihan’s Woodland Bridge which aims to soften the “harsher urban character of Dyer Avenue.”
Van Holsbeke says because the connector is public infrastructure, it was important for the design firm to maximize durability while minimizing maintenance of the two bridges.
For the timber bridge, 16-by-24-inch CLT vertical diagonals were used. The top and bottom chords were spliced together with a cross section spanning 16-by-28 inches, and are between 85 feet and 110 feet in length, he points out.
The top members and chords of the timber system have a triangular geometry to optimize water runoff.
SOM collaborated extensively with timber manufacturer Structurlam (now part of Mercer Mass Timber Group) and builder Turner Construction to develop detailing.
Van Holsbeke says among the means of achieving a modern take on a historic Warren truss bridge involved working with the contractor to develop steel connections “finely integrated and subtly revealed in the bridge, rather than a big and expressive gusset plate connection that you would have seen in the past.”
The other crossing on the Moynihan Connector, the Woodland Bridge, is made of steel, supported on architecturally exposed weathered columns and angled bracket arms, says Van Holsbeke.
SOM started designing the project for the Moynihan Connector in February 2021 and the construction was completed in June 2023.
The High Line is the seed of a nonprofit called Friends of the High Line which advocated the preservation and repurposing of the abandoned rail spur.
Work first commenced in 2006 and earlier phases of the 2.5-mile line opened in 2009, 2011 and 2014.
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