In the effort to mitigate the relentless tide of marine debris, researchers in Hawaii are experimenting with a literal road to recovery. By integrating plastic waste and discarded fishing gear into asphalt, the state is testing whether the very pollutants choking its coastlines can be repurposed as durable infrastructure.
This initiative, known as the Nets-to-Roads program, represents a significant shift in how the islands handle their unique environmental vulnerabilities. While other regions in the U.S. Have explored plastic-infused pavement, Hawaii is the first to specifically target marine debris—a critical distinction given the archipelago’s exposure to tourist waste and the Great Pacific Garbage Patch, which periodically engulfs the island chain.
The scale of the effort is already evident in the numbers. To date, 90 metric tons of plastic trash have been removed from the Pacific Ocean, and more than a metric ton of fishing nets alone have been paved into Hawaiian roads.
The Engineering Behind the ‘Nets-to-Roads’ Process
The transformation of ocean trash into a drivable surface is a multi-step logistical operation coordinated by the Center for Marine Debris Research at Hawaii Pacific University. Marine biologist Mafalda de Freitas and her colleagues lead the effort to collect and sort debris from local beaches. They specifically target polyethylene—a durable plastic commonly found in yogurt containers, milk jugs, and industrial fishing nets.
Once sorted, the waste is shipped to the U.S. Mainland to be shredded and ground into a fine powder. This material is then returned to an Oahu-based pavement production facility, where it is blended with other ingredients to create a hot asphalt mix. This mixture is then deployed to specific test sites, such as a length of road on Ewa Beach on the southwestern side of the island.
To ensure the roads are not only sustainable but functional, researchers are testing various “recipes.” Some mixtures include a rubber called styrene-butadiene-styrene, which is added to increase the flexibility and durability of the pavement, while other strips serve as controls using traditional asphalt.
Addressing the Microplastic Dilemma
The most pressing concern for the scientific community is not whether the roads will hold, but whether they will leak. There is a significant risk that the wear and tear of daily traffic could cause the plastic-infused pavement to shed microplastics back into the surrounding soil and water.
Jennifer Lynch, a chemist and head of the Center for Marine Debris Research, emphasizes the gravity of this risk. “We’re extremely concerned about the shedding of plastics or other chemicals into the environment,” Lynch says, noting that these toxic additives can lead to reproductive problems, chronic inflammation, and hormone disruption in both humans and animals.
To address this, the team conducted rigorous leaching tests. They simulated heavy stormwater by dumping sanitized, filtered water onto the road and sweeping the surface to collect gravel dust. Preliminary results, presented on March 22 at the American Chemical Society meeting in Atlanta, suggest that the asphalt remains largely intact. Jeremy Axworthy, a marine biologist and lab manager with the program, reported that there was no significant microplastic release when compared to traditional asphalt strips.
Experimental Phases and Methodology
The research is being conducted in distinct phases to isolate the variables that affect road stability and pollution:
- Phase One (2022): Three strips were laid—one traditional asphalt with rubber, one with marine waste and rubber, and one with marine waste without rubber.
- Phase Two (2024): Five experimental strips were introduced to further differentiate between the effects of ground fishing nets versus general consumer plastic waste, both with and without the addition of styrene-butadiene-styrene rubber.
To achieve a more precise quantification of polymer release, the team is currently utilizing an industrial solvent called dichlorobenzene to extract plastic polymers from road dust. These detailed results are expected in forthcoming reports.
Challenges in Scaling to a Tropical Climate
While the initial data is promising, scaling the project for statewide use requires overcoming environmental hurdles unique to the Pacific. Bill Buttlar, director of the Mizzou Asphalt Pavement and Innovation Lab at the University of Missouri in Columbia, notes that Hawaii’s geography presents challenges not found in the American Midwest.
The combination of intense tropical rainfall and volcanic activity creates a volatile underground environment. When the ground shifts due to seismic or volcanic activity, it can cause roads to crack regardless of the materials used. “The main challenge to scaling this is getting the recipe right with the asphault because what works in Hawaii may be a little different than what works in the Midwest,” Buttlar says.
| Material Source | Additive Used | Primary Goal |
|---|---|---|
| Marine Debris/Nets | Styrene-butadiene-styrene | Durability & Pollution Reduction |
| Consumer Plastic | Styrene-butadiene-styrene | Waste Diversion & Flexibility |
| Traditional Asphalt | Standard Rubber | Experimental Control |
The success of this program could provide a blueprint for other island nations facing similar crises of marine pollution. By turning a liability—the Great Pacific Garbage Patch—into a literal foundation for transportation, Hawaii is attempting to close the loop on plastic waste.
The next critical checkpoint for the project will be the release of the polymer quantification data derived from the second phase of experimental strips, which will determine if the “Nets-to-Roads” recipe is safe for large-scale implementation.
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