The 'All Iron' footbridge, promoted by the Provincial Council of Bizkaia, will connect Barakaldo and Erandio. It is conceived not just as a pedestrian or cycle bridge, but as a mobile structure designed to open over the estuary, allowing large vessels to pass while facilitating daily connections for pedestrians and cyclists.
Behind its light and curved appearance lies an engineering work of enormous precision, dictated by water, tides, port traffic, and the need for each section to fit together millimeter by millimeter. All parts are made from special S355 steel and protected with specific paints to withstand the marine environment, as the corten steel commonly used in other infrastructures was not suitable for continuous exposure to the estuary's humidity and salinity.
The structure will span 352 meters in length and six meters in width, divided between a cycle path and a separate pedestrian zone. Much of its complexity will not be visible from the outside. The deck has been divided into ten large metal sections, in addition to the two central mobile spans, and each of these is further subdivided into smaller pieces to facilitate manufacturing, transport, and assembly. These components will travel nearly 70 kilometers from Vitoria to the estuary overnight via escorted special transports, requiring the temporary removal of signs, traffic lights, or bollards along the route.
Beneath the footbridge's surface, electrical conduits, control systems, lighting, and mechanisms for coordinating the bridge's opening will run. All these will be housed in a very small, sealed interior space to protect the structure from marine corrosion. The footbridge must also withstand wind, humidity, temperature changes, and the constant movement of the estuary without losing precision in its millimeter-perfect fits.
The mobile sections will also incorporate two large conical masts, approximately nine meters in height, and a counterweight system designed to balance the structure during rotation. Technicians compare the overall operation to a clockwork mechanism, as any minimal deviation can affect the closure of the central spans. Therefore, before final installation, the mobile sections will be pre-assembled and adjusted in a pre-assembly area in Zorroza, where parts of the interior installations and mechanisms will also be fitted. Only after verifying that everything fits precisely will the pieces be transported by pontoons along the estuary to their final position.
Construction is also influenced by the water's behavior. Currents, tides, and poor underwater visibility necessitate continuous coordination of subaquatic work and estuary maneuvers. In some areas, teams must pump water to allow divers to work with some visibility amidst the mud. Once operational, the footbridge can be fully opened in about five minutes by rotating its two central sections 90 degrees clockwise. The opening will occur only for the passage of large vessels, estimated at once or twice a month, and will be signaled via signage and public address systems for pedestrians and cyclists.
