The Ponte 25 de Abril is the only route into the city of Lisbon from the south over the Tejo Estuary. It is named after the Portuguese Carnation revolution of 25 April 1974. It was previously known as the Salazar Bridge, and is often referred internationally as the Tagus River Bridge. It was designed and built by American firms and features a stiffened-truss deck with similarities to the Golden Gate Bridge.

In the 1990s the city authorities planned the addition of two carriageways and a rail crossing using the superstructure of the original road bridge. A double-track railway now runs on a lower platform within the stiffening truss. The reconfiguration of the structure required reinforcement, including a second set of main cables. Bill Brown and his colleagues at Brown Beech were consultants to American Bridge Company and the Steinman, Boynton, Gronquist & Birdsall firm on the cable spinning, carried out on the operational suspension bridge.

In 1998 the Vasco de Gama Bridge was opened to the east to relieve some of the city’s traffic congestion.