Bridge a 10-lane freeway without disrupting traffic. That was the extraordinary challenge presented by the South African Department of Transport when it prohibited lane closures during construction of a bridge to take Harper Road over the N12 freeway in Germiston. The N12 carries 230,000 vehicles daily on its 10 lanes.
The Concorde East Overpass, completed in 1995, is the three-lane bridge that met the DOT challenge. The two-span single-pylon cable-stayed structure was constructed alongside the freeway, then rotated about the pylon into its final position spanning the freeway without closing the road to traffic. The second span, which acts as a counterweight, was buried under fill and is completely invisible in the finished structure. Unique in both design and construction, the overpass is the world's shortest cable-stayed bridge open to vehicular traffic and the only such bridge in South Africa.