The new A10 highway between Bucelas and Carregado in the north of Lisbon establishes a link between the A1, A9 and A13 highways. This route crosses the valley of the Loureiro River on a 1050 m long viaduct at a height of about 90 m above water level. Two independent structures with 18,10 m wide platforms carry three traffic lanes each. The conceptual design of the bridge was guided by the interplay of the topographical and geological conditions. While economy and speed of construction were ruling principles, it has been considered that the new bridge should call forth respect for its environment and thereby for the public who pays for it. Design of the Loureiro Viaduct was determined by the topographic features of the valley, combined with the use of well known construction methods that could meet the economic requirements. The formal unity of the ensemble, the proportional equilibrium of spans and pier heights, the simplicity of the chosen forms and the clear perception of the structural behaviour resulted in an appraised solution in regard to the visual effect, structural efficiency and economy.