The New Boca del Cerro Bridge: Harmonizing Engineering and Nature on Mexico’s Tren Maya

Situated at the end of the Usumacinta River Canyon – a protected area known for its extraordinary scenery – the new Boca del Cerro Bridge represents a careful blend of innovation and restraint. The original bridge, an arch designed to handle road traffic, a railway, and pedestrians, has long been cherished as an engineering milestone. With its 150-meter span, it was built using cantilevered construction of the steel arch’s trusses, a method that was groundbreaking in its time. 

Today, that same pioneering spirit is evident. Building a second bridge parallel to this historic structure required advanced technical solutions and sensitivity to the protected landscape. Engineers faced a dual challenge: maintaining harmony with the environment and respecting the historical significance of the existing bridge while creating a structure capable of supporting modern rail infrastructure. The new Boca del Cerro Bridge adopts contemporary truss technology but remains visually unobtrusive, echoing the contours of the natural surroundings and the existing structure.

The new bridge was constructed to provide essential connectivity without disrupting the landscape or overshadowing the historical bridge. Placed parallel to the original and painted in a subdued dark green, it intentionally fades into the canyon when viewed from downstream, creating the illusion of a single bridge. The bridge extends 160 meters across the river and is anchored by concrete spans at each end.

One of the most distinctive aspects of the design is its variable-depth composite truss, chosen to create a sense of lightness while providing the necessary structural integrity. Inspired by a similar design used in the Ulla River viaduct, the bridge features a Warren-type truss with double composite action – using steel and concrete together to reduce the amount of steel required. This choice minimizes environmental impact while ensuring performance and stability for the heavy railway traffic it will carry.

Building a bridge over the Usumacinta, Mexico’s fastest-flowing river, was no small task. The design team needed a process that would protect the river and the surrounding area. The team opted for an incremental cantilevered erection, allowing the truss to extend from both sides without requiring construction equipment in the river. This approach was critical, considering the variability of river levels and the need to safeguard the protected environment.

The bridge’s design thoughtfully blends practicality and elegance. Its Warren truss configuration reduces the connection points needed, optimizing the steel construction and ensuring reliability against the heavy, repetitive loads of railway traffic. Engineers incorporated subtle, rounded transitions between plates and smooth welds to enhance the structure’s appearance and longevity. By modeling every detail with Building Information Modeling software, the team minimized the risk of surprises during construction, ensuring efficiency and accuracy down to the smallest joint.
 

To support the railway, the bridge’s deck consists of a concrete slab on top of the steel truss, reducing compression stress in critical zones and enhancing durability. Likewise, along hogging zones, a bottom concrete slab reduces the compression stresses in those zones. This dual-material approach, using steel and concrete where most effective, speaks to the design’s ingenuity in creating a robust yet efficient structure.

The Boca del Cerro Bridge isn’t solely an engineering project – it’s also a symbol of Mexico’s commitment to balancing progress with preservation. By enabling greater accessibility across the Yucatán Peninsula, the bridge plays a vital role in the Tren Maya’s mission of economic and tourism development, linking bustling tourist destinations with inland communities. And yet, the design prioritizes the local landscape, with a structure that honors the natural and cultural heritage of the area.

As it quietly and elegantly spans the river, the Boca del Cerro Bridge showcases how we can thoughtfully integrate infrastructure projects into sensitive environments. It is a reminder that modern engineering, when guided by respect for history and nature, can create connections that bridge the past with the future.