60,000 miles of US roads could be under water in a few decades. Here's how experts say we can save our critical infrastructure.

• Sea levels along the US coastline could rise 10 to 12 inches over the next 30 years. 
• Damages on roads were about $1.5 billion in 2020 and could be as high as $37 billion in 2050. 
• A massive coastal barrier off the coast of Texas is an example of what could improve resiliency. 

Chris Hamilton is a bike enthusiast. Almost every day, he rides around his hometown of Key West, Florida, where he moved from Washington D.C. 7 years ago. Each time, he sees new houses being built, rising higher with every construction.

"In the Keys, if you redo your house, you have to mitigate it for sea level rise," he told Insider. "And so, up and down the streets, all of a sudden you'll see a house that's three or four feet higher, or six or seven or eight feet higher. In some places all the new houses begin at 15 feet," above sea level. 

The postcard-famous Florida Keys are a chain of islands connected to Miami by a 165 miles stretch of US Highway 1 known as the Overseas Highway thanks to its extensive network of bridges. The islands are particularly exposed to rising sea levels. In 2019, some of its roads and neighborhoods were flooded for 82 days straight.

Across the country, more than 60,000 miles of roads and bridges near coastal areas are facing a similar fate, experts say. Rising sea levels and more extreme flooding brought on by climate change threaten billions of dollars of economic consequences and have experts urging officials to find speedy solutions to ensure resilience.

Roadways are the lifeline

Smaller, coastal communities like Key West are at the forefront of the sea level rise, but the main arteries of the vast US road network are just a few miles behind. 

"Roadways are increasingly going to become exposed to high tides and storm surge," William Sweet, an oceanographer at the National Oceanic and Atmospheric Administration told Insider. "Because they're on the ground and there's not much we can do about that without taking some serious preventative action."

Across the country, you can expect coastlines to rise an average of 10 to 12 inches over the next 30 years, according NOAA's Sea Level Rise Viewer, which lets you adjust sea level rise and visualize how in trouble your house or your commute might be. 

The team Sweet is part of, which studies the impact on roads and traffic of high tide flooding, the kind that can happen on a sunny day even without big storms, estimates there was about $1.5 billion worth of damage in 2020. By 2050, they say it'll be as high as $37 billion.

The costs include a number of direct and indirect consequences of frequent flooding. 

"You have places that will be flooded out, so physically you can't leave or you can't get there," Katy Serafin, a coastal scientist at the University of Florida, said. "But then you can also have delays and traffic in places that are really far away from the flood zones, as people have to take alternative routes."

NOAA's Sweet recommends departments of transportation across the country start identifying and prioritizing the most critical parts of their road network, the ones that connect ports, cities, and railroads and are critical to the economics of an area. 

'We're not too late' 

Chris Hamilton, who worked for the Department of Transportation in Virginia before his early retirement in Key West, said he wasn't optimistic about the Florida's resiliency up until a few months ago. 

Then, he started doing what NOAA recommends, reading about sea level rise and the plans that individual communities are studying to increase their own resiliency. 

Monroe County, for example, where the Keys are located, projects a sea level rise of 5.5 feet in 78 years — not great considering the islands have an average elevation of 3.2 feet.  

The county is studying a plan to progressively raise roads to make them less vulnerable, among other things, a project that may cost nearly $2 billion. 

Similar plans, projects and studies are being developed all over the US' coastal communities. Miami is working to rise the surface of some of its roads, for example, while New York is getting ready to build a sea barrier.

The Dutch are onto something

If there's a country that knows a thing or two about floods, it's the Netherlands. Almost a third of it is below the sea level, after all. 

For years, the Dutch have raised sea barriers across their rivers' estuaries and built levees. In the Netherlands Delta Program, which was introduced in 2010, the unpredictable nature of climate change and rising sea levels — we know they're rising, but it's hard to know how fast —  is taken into account from the very beginning. 

It's not a matter of how the situation is going to be in 50 or 100 years anymore, and how to fix that now — it's hard to raise the surface of all the coastal roads in the US at the same time — but how to have a long term plan that includes a number of smaller, more achievable steps. 

"So you're not trying to predict the future anymore," Lewis E. Link, a senior research engineer at University of Maryland "You're not trying to say 'what it's going to be in 2050, or 2100?' But you're understanding how sensitive you are to different levels of change. And now you have some idea of where your Achilles heel is with regard to flood protection, you can do an incremental adaptation." 

The Coastal Texas Program, a resiliency strategy that addresses "a wide array of immediate and long-term" needs across the coast of Texas, takes a similar approach. The program plans to build "multiple lines of defense" against hurricanes, storms, and rising sea levels, and the Federal Government gave the U.S. Army Corps of Engineers' the green light to start implementing it in December of 2022.

Part of it is the Galveston Coastal Barrier — nicknamed the "Ike Dike" after the 2008 Hurricane Ike, which caused a deadly storm surge on Galveston Island and Bolivar Peninsula and is considered one of the costliest US hurricanes. 

The project could cost up to $34 billion. 

"The initial design allows for a step A, a step B, and a step C if changes have to be made," Link pointed out. 

By understanding how to adapt incrementally, and starting to act as soon as possible, the US can learn how to adapt to rising sea levels. 

"We're not too late," NOAA's Sweet said. "But now's the time to be aware and repair."