The current Gallaraga bridge, which spans the Cadagua River in the municipality of Sodupe, lacks sufficient hydraulic capacity to handle the river’s flood events. It is an old structure consisting of massive masonry semi-circular arches, with an approximate length of 30 m and a deck width of 10.60 m. The bridge is composed of three vaults: the central vault has an approximate radius of 5 m, while the lateral vaults have a radius of 2.50 m. These vaults rest on two central piers—which feature cutwaters (starlings) on the upstream side—and on ashlar masonry abutments at the ends. In the late 20th century, the platform was widened using a concrete deck that rested on the existing bridge; the sidewalks are located on the cantilevers of this new deck.

The bridge’s poor flow capacity and its structural typology made it necessary to replace it with a single-span structure that is more slender and features an improved road profile.

The site and the span to be crossed led to an extensive study of various design solutions based on steel girder structures:

• Steel bridge with two box girders below road level; pinned-fixed supports.
• Steel bridge with two box girders below road level; pinned-fixed supports, lightened at the fixed connection.
• Steel bridge with two box girders below road level; fixed-fixed supports.
• Steel bridge with two box girders above road level in the central section; fixed-fixed  supports.
• Steel bridge, bowstring solution in the central section; fixed-fixed supports with diagonals/verticals.
• Steel bridge, bowstring solution; pinned-fixed  supports with vertical members.
• Steel bridge, bowstring solution.

Ultimately, it was concluded that the most suitable alternative was the fixed-fixed  bowstring with vertical members, which was the option developed in the final construction project. Consequently, the new bridge will feature a steel deck composed of a tied-arch structure, where the bottom chord consists of closed steel box girders with variable depth along their length. To ensure sufficient clearance for road traffic during entry and exit alignment transitions, the design incorporates rigid restraints within the abutments, allowing the arch to join the bottom chord nearly 5.00 m before reaching them. This configuration is achieved through two short spans within the abutment structure, resulting in a spacing of 39.35 m between the axes of the anchored bearings, while the distance between the front abutment bearings is 31.45 m

In cross-section, the arch is double, with a separation of 7.35 m between the arch axes and a total structure width of 12.40 m. The carriageway, 7.00 m wide and housing two 3.50 m traffic lanes, is situated between the two arches, which in turn serve as a barrier between vehicular traffic and the pedestrian traffic that runs along 2.10 m wide walkways supported by the exterior cantilevers.