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The New Coastal Road: Building a Highway Around an Island

It is said to be France’s most expensive road project – but it’s not actually in France. It’s a road, but the vast majority of it doesn’t run over land. Confused? 

The New Coastal Road which is being constructed on the French overseas department of Reunion in the Indian Ocean is set to be one of the most eye-catching new mega projects due to appear soon. At only 12.5 km (7.7 miles) in length, it certainly isn’t its size that’s impressive but instead of revamping the old dangerous road that runs close to the cliff, planners have designed a road that will use a series of platforms and a viaduct to run across the ocean rather than the land. 

The road will connect two of the main residential areas on Reunion, Saint-Denis, the largest city, and La Possession to the west. It was initially hoped it would be ready in 2020 – but that seems to have come and gone. With costs now soaring up to €1.6 billion (that’s close to $2 billion), this is a mightily expensive piece of road when we look at its cost per km basis.    


The small island of Reunion lies east of Madagascar in the expansive Indian Ocean. It measures 63 km (39 miles) long by 45 km (27.9 miles) wide and has a population of 859,000. The island’s landmass is just over 2,500 sq km (965sq miles) but the majority of this is mountainous. In fact, not only is it mountainous, it’s volcanic, with the extinct Piton des Neiges measuring 3,070 metres (10,072 ft) and the very much active Piton de la Fournaise at 2,631 metres (8631ft) – known locally as Le Volcan – which sounds a little ominous to me.  

And Le Volcan isn’t one of those active volcanoes that is happy to just sit around and relax. The eruption in 2007 was the largest in over 100 years and produced a staggering 3 million cubic metres (105 million cubic ft) of lava per day for nine days. Then there was the 2004 eruption, and 2015, 2016, 2019 oh and the recent eruption in December 2020 – anyway, I’m sure you get my drift. This is one of the most active volcanoes anywhere on the planet. 

The island’s principal industries are rum and sugar production, but it has seen a steady rise in tourism in recent years. That being said, Reunion suffers from painfully high unemployment which has remained for decades now. The unemployment rate in 2016 was 23% – the lowest it had been since 2008.   

The makeup of the landmass makes expansion particularly difficult. Most residential areas are wedged along the coast with roads heading inland invariably small, windy and potentially dangerous. The current road that snakes around the island is known as the RN1, a four-lane highway that no doubt has its charms but also plenty of limitations. Like any road built at the foot of steep cliffs, you may often find it closed because of rockfalls, while adverse weather is also known to cause the closure of this vital connection between residential areas. On average, the road is closed 40 times per year, which no doubt is a real pain for those living nearby. What’s even worse is that rockfalls have killed 23 motorists over the last decade. So basically, this is a terrible place for a road.   

The Plan

The new coastal road has been designed to relieve the pressure from the smaller RN1 and will lie between 80 and 300 metres from the shore while curving around to follow the island’s coast. The road will run from Saint Demis to La Possession just over 16 km away with the most visually striking component being the 5.4 km (3.3 miles) viaduct, along with three intersections where it connects with other roads and six sea embankment sections. 

Now, that makes everything sound fairly straightforward, but the challenges involved with building the new coastal road are enormous. Let’s start with the wind. This is an area of the world that tends to get battered by cyclones regularly. The road needs to be able to withstand winds of up to 300 km/h (186 mph). Then there is the obvious problem of waves crashing into the structure day in and day out for years to come. And to top it all off (and remember that this is the volcano capital of the world – that’s my own accolade there not from any official sources), it’s also an area prone to the odd earthquake every now and again. So, we’ve got cyclones, thunderous waves, volcanoes and earthquakes – if that’s not a significant set of challenges I really don’t know what is. 

But what is life without a good challenge? Not only will the new road greatly reduce congestion in the local area, but it’s hoped that it could lead to further investment on the island, while also providing over 18,000 jobs in the meantime.


Work on the coastal road began back in 2013 and is being built by French consortium including Bouygues Travaux Publics, VINCI Construction Grands Projets, Dodin Campenon Bernard and Demathieu Bard Construction. 

In total, the road will use 48 large platforms which were prefabricated at a production plant nearby before being moved down to the ocean. This was done to negate the impact on local wildlife and flora, but also saved the construction team the nightmarish job of trying to build these platforms in rough seas. The platforms are between 24 and 38 meters (78-124ft) tall, with between 12 and 15 meters (39-49ft below sea level, and between 3 and 8 metres (9.8-26.2ft) below the ocean floor. 

Key to the entire project has been the massive Zourite (creole for octopus). This mega-barge, used to manoeuvre the platforms into place, was built in Poland specifically for the project and is roughly the size of a football pitch. On top of that, the project is also using the world’s largest offshore overhead travel crane which is secured to a floating platform. This includes two pairs of lifting beams and is 30 metres (98.4 ft) in width. The crane is used to anchor the platforms securely on the ocean floor before lifting other prefabricated sections into place – as you can imagine, it’s not a quick process.    

The viaduct will be both impressive and the most difficult section of the road to build. It contains 36 main pier sections and 1,386 precast segments, each weighing between 210 and 285 tons. A specially designed launching girder, measuring 278 metres (912ft) in length and weighing 2,600 tons, was constructed and supports the work going on beneath it. The massive girder is then slowly advanced as the platforms and road below it are installed and is designed to be able to withstand 240 km/h (149mph) cyclonic winds. 

The viaduct was produced using 300,000 cubic metres (10.5 million cubic ft) of concrete and 52,000 tons of steels. The structure that forms the New Coastal Road has a predicted life cycle of 100 years. Now, 100 years isn’t exactly a short time, but it’s not exactly a long time either. The fact that this will all need to be replaced in a century says a lot about the strain that building in these kinds of conditions puts on even the sturdiest of materials.

While most of the attention is reserved for the road itself, the embankment below acts as its vital shield against the mighty ocean. 19 million tons of rock, gravel and sand was brought down to the coast from quarries around the island to form the foundations of this embankment. Along with that, 38,500 hard shell accropodes, which are those strange shaped concrete objects designed to protect coastal structures were also added. In total, these accropodes weigh a colossal 780,000 tons and they were by no means scattered randomly. Each one contains the equivalent of a black box which allowed them to be lowered by cranes with pinpoint accuracy in a pre-designed pattern to maximize the coastal defence.   

There was also plenty of consideration regarding the impact on wildlife as construction progressed. As you can imagine, this kind of building work is incredibly noisy and that noise can be harmful to cetaceans, such as whales and dolphins. To remedy this – or to try at least – sound barriers were installed near areas of offshore work. This was done using bubble curtains which is a system where bubbles are produced in a deliberate arrangement that then acts as a pneumatic barrier. The same kind of system is often used to combat oil spills or to block entrances to harbours.      


There has been some controversy surrounding this project, with some in France questioning whether this kind of money should be spent on an overseas department so far from the mainland. Some see the project as extravagant and over the top and have queried whether it could have been done on a significantly smaller budget. 

Those on the island seem united in the need for the new coast road, but there has been some animosity regarding some of the quarries that have been opened. A recent court hearing ruled that some of the environmental reports done on the quarries and the effects of dust in the area are inaccurate. And in any case, the project has suffered from a shortage of rock and sand on the island with barges and aircraft now bringing over materials from Madagascar.    

A Road to Remember

There seems to be a little confusing over just when the New Coastal Road on Reunion will finally open. There are whispers of a late 2021 opening but the local government has stated it’s now on schedule for a 2022 completion. 

With its original cost estimate of €700 million now more than doubled, it’s not difficult to understand why some see this as an overly ambitious project. The French have a complicated relationship with their overseas departments, as do many nations who still own distant lands gained long ago. Large-scale and costly infrastructure projects are often met with barely muted grumbles from the mainland. The idea of distant outposts scattered around the globe sounds appealing, just as long as they don’t cost too much money. 

But while this project certainly has some extravagance to it, there weren’t actually many other options. On a small island like Reunion space is at a premium and its ageing transport system can hardly support its ever-growing population. The conquering of the water will mean faster and easier movement around this section of the island with high hopes that it could lead to some kind of rejuvenation for an island that is still badly suffering from the fall out of the 2008 recession. 

It may be a relatively short distance, but the New Coastal Road on Reunion is going to provide one hell of a road trip when it’s finally done. 

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