New Coastal Road viaduct on Reunion Island

Setting new standards for durable design, future-proofing, biodiversity and resilience to extreme conditions and climate change.

The new highway linking the Reunion’s Saint-Denis and La Possession was designed to replace the former Route du Littoral, a perfect example of vulnerable infrastructure faced with natural hazards that runs along the coast and is the only main transport corridor available between capital and major port.

To replace that, the new highway has been designed to last 100 years, is adaptable to multimodal use throughout its lifespan, and will withstand some of the world’s most extreme marine weather conditions.

Its design includes a remarkable viaduct approximately 5,400m in length that rests on 48 piers in the sea. This structure is now possibly the most durable and reliable such highway in the world, having been designed by Egis to withstand the most violent hazards, including cyclonic swells, cyclones, high temperatures, heavy rainfall, seismic events, vessel collisions and more.

Its design includes a remarkable viaduct approximately 5,400m in length that rests on 48 piers in the sea. This structure is now possibly the most durable and reliable such highway in the world, having been designed by Egis to withstand the most violent hazards, including cyclonic swells, cyclones, high temperatures, heavy rainfall, seismic events, vessel collisions and more.

Can roads really be sustainable?

Built along a biodiverse coastline, the new road has been future proofed with six lanes to accommodate traffic growth, with two lanes convertible to light rail in future. But perhaps the most extraordinary effort for sustainability came in addressing biodiversity.

The Reunion coastline is rich in both flora and fauna, particularly with endemic species. The seas over which parts of the road now run, are also home to humpback whales and dolphins, as well as corals and numerous breeds of local birds.

To put a road through this environment was a unique sustainability challenge but in doing so, it has become something of a case study for how to do it well. Egis undertook in-depth and innovative environmental studies covering issues like ecology, marine acoustics and sedimentology to inform design and delivery.

A coral bed was found on site, so in order to prevent the natural marine habitats from being covered up, an anti-suspended matter barrier was set up between the work zone and the coral bank. In addition, a marine corridor was designed into the project to encourage the migratory maturation of juveniles from the coast to their adult refuge habitats offshore.

Viaduct piers have even been eco-designed to provide nursery areas and, further out to sea, eco-reefs were laid out to enable ecologically sustainable development across the project area.

The Award of Excellence was given to this project, as part of the 2021 FIDIC Project Awards, with eight global projects identified on the basis of sustainability and impact.