From lower carbon emissions to fewer potholes, there are a number of benefits to building a layer of plastic into roads.

On a road into New Delhi, countless cars a day speed over tonnes of plastic bags, bottle tops and discarded polystyrene cups. In a single kilometre, a driver covers one tonne of plastic waste. But far from being an unpleasant journey through a sea of litter, this road is smooth and well-maintained – in fact the plastic that each driver passes over isn’t visible to the naked eye. It is simply a part of the road.

This road, stretching from New Delhi to nearby Meerut, was laid using a system developed by Rajagopalan Vasudevan, a professor of chemistry at the Thiagarajar College of Engineering in India, which replaces 10% of a road’s bitumen with repurposed plastic waste.

India has been leading the world in experimenting with plastic-tar roads since the early 2000s. But a growing number of countries are beginning to follow suit. From Ghana to the Netherlands, building plastic into roads and pathways is helping to save carbon emissions, keep plastic from the oceans and landfill, and improve the life-expectancy of the average road.

By 2040, there is set to be 1.3 billion tonnes of plastic in the environment globally. India alone already generates more than 3.3 million tonnes of plastic a year – which was one of the motivators behind Vasudevan’s system for incorporating waste into roads.

It has the benefit of being a very simple process, requiring little high-tech machinery. First, the shredded plastic waste is scattered onto an aggregate of crushed stones and sand before being heated to about 170C – hot enough to melt the waste. The melted plastics then coat the aggregate in a thin layer. Then heated bitumen is added on top, which helps to solidify the aggregate, and the mixture is complete.

Many different types of plastics can be added to the mix: carrier bags, disposable cups, hard-to-recycle multi-layer films and polyethylene and polypropylene foams have all found their way into India’s roads, and they don’t have to be sorted or cleaned before shredding.

As well as ensuring these plastics don’t go to landfill, incinerator or the ocean, there is some evidence that the plastic also helps the road function better. Adding plastic to roads appears to slow their deterioration and minimise potholes. The plastic content improves the surface’s flexibility, and after 10 years Vasudevan’s earliest plastic roads showed no signs of potholes. Though as many of these roads are still relatively young, their long-term durability remains to be tested.

By Vasudevan’s calculations, incorporating the waste plastic instead of incinerating it also saves three tonnes of carbon dioxide for every kilometre of road. And there are economic benefits too, with the incorporation of plastic resulting in savings of roughly $670 (£480) per kilometre of road.

In 2015, the Indian government made it mandatory for plastic waste to be used in constructing roads near large cities of more than 500,000 people, after Vasudevan gave his patent for the system to the government for free. A single lane of ordinary road requires 10 tonnes of bitumen per kilometre, and with India laying thousands of kilometres of roads a year, the potential to put plastic waste to use quickly adds up. So far, 2,500km (1,560 miles) of these plastic-tar roads have been laid in the country.

“Plastic-tar road can withstand both heavy load and heavy traffic,” says Vasudevan. “[It is] not affected by rain or stagnated water.”

Similar projects have emerged around the world. The chemicals firm Dow has been implementing projects using polyethylene-rich recycled plastics in the US and Asia Pacific. The first in the UK was built in Scotland in 2019 by the plastic road builder MacRebur, which has laid plastic roads from Slovakia to South Africa.

MacRebur has also found that incorporating plastic improves roads’ flexibility, helping them cope better with expansion and contraction due to temperature changes, leading to fewer potholes – and where potholes do happen, filling them in with waste plastic otherwise destined for landfill is a quick fix. The UK government recently announced £1.6m for research on plastic roads to help fix and prevent potholes.

In the Netherlands, PlasticRoad built the world’s first recycled-plastic cycle path in 2018, and recorded its millionth crossing in late May 2020. The company shredded, sorted and cleaned plastic waste collected locally, before extracting polypropylene from the mix – the kind of plastic typically found in festival mugs, cosmetics packaging, bottle caps and plastic straws.

Unlike the plastic-tar roads laid in India, the UK and elsewhere, PlasticRoad doesn’t use any bitumen at all. “[PlasticRoad] consists almost entirely of recycled plastic, with only a very thin layer of mineral aggregate on the top deck,” says Anna Koudstaal, the company’s co-founder.

Each square metre of the plastic cycle path incorporates more than 25kg of recycled plastic waste, which cuts carbon emission by up to 52% compared to manufacturing a conventional tile-paved bike path, Koudstaal says.

But once the plastic is inside a path or road – how do you make sure it stays there? Might the plastic content be worn down into microplastics that pollute soil, water and air?

Ordinary roads, tyres and car brakes are already known to be a major source of microplastic pollution. Koudstaal says that plastic-containing paths do not produce more microplastics than a traditional road, as users don’t come into direct contact with the plastic.

The other potential point where microplastics could be released from the paths is from below: the paths are designed to allow rainwater to filter through them, trickling down through a drainage system beneath the path’s surface. But Koudstaal says microplastics are unlikely to leave this way either: “The bike paths include a filter that cleans out microplastics, and ensure rainwater infiltrates into the ground cleanly.”

Gurmel Ghataora, senior lecturer at the department of civil engineering at the University of Birmingham, agrees that using plastics in the lower surfaces of the road minimises the risk of generating additional microplastics. “It is inevitable that such particles may be generated [at surface level] due to traffic wear,” he says.

With India home to one of the world’s largest road networks, growing at a rate of nearly 10,000km of roads a year, the potential to put plastic waste to use is considerable. Though this technology is relatively new for India, and indeed the rest of the world, Vasudevan is confident that plastic roads will continue to gain popularity, not only for environmental reasons, but for their potential to make longer-lasting, more resilient roads.