Plastic is eating the roads. It might be a cleaner, quieter, ready-made alternative to asphalt for the next generation of paving.
The asphalt on our roads is made of an aggregate, often rocks, sand, and gravel bound by a sticky substance called bitumen.
Since at least the fifth century BC, humans used naturally occurring bitumen for waterproofing ships, adhering bricks, and embalming mummies. After 2,000 years in these bit player roles, bitumen hit the big time in 1830s Europe as an input to asphalt roads.
Today, bitumen is made from crude oil. It’s a sticky black product, the last bit out of the fractional process after petrol, diesel, butane, kerosene, and so on have all been extracted.
In the last 15 years, a small group of environmentally minded engineers and designers pioneered innovations that bind asphalt with plastic rather than bitumen. A few have even built roads entirely of plastic, replacing the asphalt surface and deeper structures that usually need heavy earthworks.
Proponents claim that plastic roads offer major improvements in design, cost, and quality while also serving as an outlet for waste plastic. Critics argue that plastic roads are empty ‘green’ hype or can’t compete with the benefits of traditional asphalt. The truth is most likely that using plastics in road building does have real environmental, cost, and structural benefits. But, outside of niches like bike paths and pedestrian paths, innovations still have yet to reach the scale and capabilities of the traditional asphalt road.
The road to innovation
Any innovation in road building faces an uphill battle. Asphalt has strong merits. It’s quiet. It has good ridability – it feels good to drive on – and provides safe friction for tires. It’s not attractive, but not especially ugly. Maintenance may be noisy and smelly, but it’s a straightforward process of laying new asphalt sheets. Governments value this simple, well-known maintenance process. To dethrone asphalt, any innovation must improve on these many good attributes.
The market for roads hesitates to change. ‘There hasn’t been much innovation in road building materials or its construction processes in recent years’, civil engineer Luke Weatherstone of BridgeBlog said in an interview. ‘Both contractors and government bodies are very risk averse.’ If a city adopts a wild-eyed new road technology and it fails, they risk losing millions, upsetting taxpayers, and looking incompetent. ‘If it goes horribly wrong, the public will be up in arms’, says Weatherstone, ‘The product has to be superior to asphalt on cost, performance, and environmental outcomes to offset those negatives. It’s a risk analysis that’s hard to beat.’
Road building is also not a typical market. Contractors work with a relatively small number of locally monopsonistic municipalities and government offices. Contracts are long-term affairs. Contractors have little incentive to persuade their clients to adopt something new – especially if it cuts into their margins. In the short term, the new technology looks expensive and risky. Unfortunately for would-be innovators, city budgets are almost always short-term affairs.
Roads are also a highly regulated technology. Governments and engineering organizations set rigorous standards for road building. For example, American states like Colorado publish hundreds-of-pages-long mandatory specification manuals that detail requirements ranging from how earthworks should be measured to the mineral content in pavement to how delivery tickets for shipments of concrete must be written. New technology must comply with or change these standards to reach widespread market adoption.
Our inability to improve roads might also be symptomatic of our failure to improve construction more broadly. In the United States, construction speed and cost and quality of roads have all moved in the wrong direction. For example, the cost of building a mile of American roadway has tripled in real terms since the 1960s, to over $30 million.
These cost increases don’t track to higher wages or inflated input materials. And despite bigger budgets, quality has fallen. ‘There is widespread consensus’, write Leah Brooks and Zachary Liscow in Infrastructure Costs, ‘that US infrastructure quality has been on the decline.’ In their 2021 “Infrastructure Report Card”, the American Society of Civil Engineers gave American roads the less-than-reassuring grade of D. But to the pioneers of plastic roads, this dysfunction looks like opportunity.
The plastic man of India
Plastic roads began in India. In the late 1990s and early 2000s, governments in India began to restrict and then ban single-use plastic such as disposable plastic bags.
Rajagopalan Vasudevan, an engineering professor at the Thiagarajar College of Engineering, worried that bans would hurt India’s poorest families. While many governments have demonized plastic (and plastic bags in particular), the cheapness and durability of plastic make it the affordable choice to package necessities like cleaning chemicals and bagged water. Poorer families are more likely to buy the smaller quantities of products in single-use plastic packaging. Finding a way to repurpose used plastic waste would be better than a ban, reasoned Vasudevan.
Vasudevan began to tinker with waste plastic in his waste management lab. He noticed that molten plastic bonded well with the stone aggregates used in asphalt.
Vasudevan made asphalt mixtures that replaced some of the petroleum-derived bitumen binding agent with molten plastic. This new material – ‘plastic asphalt’ – looks, feels, and sounds nearly identical to traditional asphalt. But it’s tougher than traditional asphalt while also repurposing plastic waste. Tests revealed that plastic asphalt slows pothole formation and helps resist rainwater, especially important during India’s monsoons.
Most recycling uses the same types of plastic – usually thicker, harder, larger items like jugs and bottles (which is why so much plastic still ends up in landfills even in places with recycling programs). But Vasudevan’s process repurposes hard-to-recycle plastics like single-use grocery bags and thin plastic packaging. Sorting plastics can also be complicated and expensive, but Vasudevan’s shredded plastics form a composite, so recyclers don’t need to sort plastic types. Plastic asphalt is a waste sink: plastic in, plastic asphalt out. It also uses less new material derived from petroleum since it replaces some bitumen.
Vasudevan’s own research argues that waste plastics are moldable enough for plastic asphalt at relatively low temperatures. These low temperatures are too low to release toxic gasses during production, he argues. But other researchers suggest that Vasudevan’s conclusions are premature and toxic emissions during the plastic asphalt production process may be happening and must be studied.
Roads are high-stress environments for plastic asphalt. One worry of using plastic in asphalt is that the mix breaks down when exposed to heat, light, and friction. Vasudevan argues that these risks are overstated. The hot bitumen and stone homogenize the plastic, he says, so there’s little risk of microplastic run off. But recent research and laboratory tests suggest that plastic asphalt may release microplastics under normal roadway conditions. These environmental costs should be weighed against the known pollution caused by asphalt roads.
After years of advocacy by Vasudevan, plastic asphalt found champions in India’s government. Cities like Chennai, Pune, and Jamshedpur started to pave utility roads, driveways, and accessory paths with plastic asphalt. By 2020, India had paved tens of thousands of kilometers of plastic asphalt roads, mostly within cities (India’s national highways still use traditional asphalt). Some research seems to validate Vasudevan’s claims these plastic asphalt roads have proven more durable and lower maintenance over time.
Vasudevan patented his techniques and shared the patent for anyone to use. In faraway Scotland, another innovator prepared to compete with Vasudevan’s methods.
The rise of plastic asphalt
By the 2010s, Vasudevan’s methods had spread far and wide. Scottish engineer Toby McCartney entered the fray.
McCartney claims to have been inspired to make plastic asphalt in India – but not by Vasudevan. While working in southern India with a charity, McCartney noticed an informal practice where local trash pickers filled potholes with plastic waste and set it on fire. Melted plastic mixed with dirt and gravel to fill holes and cracks. McCartney, an electrical engineer by trade, wondered if this informal practice might be refined into a new technique for road maintenance.
McCartney returned home and founded Macrebur, a plastic road company of which he’s currently CEO. As with Vasudevan’s method, Macrebur replaces a large percentage of the bitumen in roads with plastic waste. Macrebur sources from UK households, businesses, and farms but ships its product around the world. Each mile of Macrebur road, McCartney boasts, contains the equivalent of one million plastic bags.
Macrebur designed its own industrial process for plastic asphalt. As with Vasudevan’s method, Macrebur’s mix focuses on plastics that can’t be recycled with traditional methods, like plastic bags and bottle tops. Macrebur combines plastic pellets with small amounts of bitumen and sells these mixes.
McCartney argues that his plastic asphalt has cost-saving and durability benefits and that the Macrebur process replaces a higher quantity of bitumen than other methods. Research on Macrebur’s products by the University of the Sunshine Coast in Australia seems to validate some of the company’s claims about Macrebur’s superior durability to traditional asphalt.
In 2016, Macrebur caught the eye of Sir Richard Branson and other prominent investors, who awarded the company a cash prize and marketing assistance. Then, in 2019, Macrebur received £1.6 million to pilot their technology throughout the United Kingdom and expanded across the UK to places like London, Bristol, and Cumbria. International customers called. Macrebur now has projects in South Africa, Australia, Slovakia, Dubai, Estonia, the United States, and more.
While Macrebur took plastic asphalt to new heights of engineering, two Dutch designers began to sketch a radical new concept: roads made almost entirely of plastic.
Roads are much more than surface pavement. Roads require earthworks and construction to create a usable base for the asphalt. These construction processes are noisy, polluting, labor-intensive, slow, and expensive, whether or not you use plastic asphalt as the road’s surface.
Major improvements in the cost and performance of roads may require a more fundamental change than what plastic asphalt can offer. In 2013, Dutch designers Simon Jorritsma and Anne Koudstaal sketched just such a novel idea: roads of interlocking, modular stretches of plastic.
While McCartney’s and Vasudevan’s plastic asphalts focus on the surface of roads, Jorritsma and Koudstaal’s innovation focuses on what lies beneath. The concept, called the Plasticroad, claims not just the plastic-waste-absorbing benefits of plastic asphalt but radical changes to road construction itself.
Their method molds waste plastic into lightweight, prefabricated stretches of road, each a few meters long. Plasticroad is 100 percent recycled plastic. But Plasticroad is a base, not a pavement surface. A thin layer of aggregate, called the wearing course, covers the Plasticroad to provide appropriate levels of noise and grip for drivers. Since they use a thin layer of traditional surface covering, Plasticroads look and sound similar to traditional asphalt. But the similarities end there.
Plasticroad pieces snap together like giant Lego bricks. Each piece has a hollow core. This has several benefits.
First, cities can run fiber-optic cables or electrical conduits through hooks along the edges of the Plasticroad. Maintenance requires five to ten centimeters of digging to access the infrastructure – whereas cables are 18–24 inches under traditional roads. Larger infrastructure like water pipes can be buried beneath Plasticroad. As with traditional roads, Plasticroad must be removed to access this buried infrastructure. Proponents argue that the design of Plasticroad lowers the hassle of this maintenance: Rather than removing and repaving asphalt, cities can detach a segment of Plasticroad, make a fix, and then snap it back into place.
The molecular properties of plastic make Plasticroad adjust to extreme hot and cold better than traditional asphalt. Since it’s hollow, Plasticroad also handles water differently. The company that produces Plasticroad argues that its design can extend – or even replace – cities’ storm sewers. Traditional asphalt absorbs some rainwater, but unabsorbed water runs off the road into ditches or storm sewers. Plasticroad doesn’t absorb water at all. Rather, it gradually filters it to surrounding subsoil through a porous bottom layer. If the soil is saturated, Plasticroad stores water within its hollow core for filtering later.
Jorritsma and Koudstaal’s work caught the eye of industry. Construction firm Volkerwessels, plastic manufacturer Wavin, and oil and gas company Total formed a joint venture in 2020 to develop and commercialize the product.
Like Macrebur or Vasudevan’s plastic asphalt, Plasticroad makes an environmental case. The roads are an outlet for waste plastic. And when a piece breaks down, it’s melted and molded into a new stretch. Its creators call it ‘circular infrastructure’.
But Plasticroads earliest adopters seem compelled by the business case. The lightweight deck that sits atop the Plasticroad lasts 30 years – about ten years longer than typical asphalt – and the subsurface base lasts 50 years – similar to hard-to-maintain concrete roads.
Carbon-focused cities can complete the whole construction process with lighter electric machinery (rather than typical diesel machines) and no expensive earthworks. Plasticroad claims 80 percent lower transport costs, 75 percent fewer raw materials, 70 percent faster construction, and a lower total cost of ownership since the road’s modularity makes maintenance easier and cheaper – though it is difficult to find authoritative per-mile cost comparisons.
After several years of prototyping and feasibility studies, Jorritsma and Koudstaal built the first Plasticroad in 2018: bike paths in the cities of Zwolle and Giethoorn in the Netherlands.
Plasticroad went viral on social media in 2019. The proposal has attracted critics ever since. Plasticroad claims that the surface layer insulates its plastic base from UV exposure and friction, which stops microplastic runoff – though there may still be the risk of the hollow plastic core leeching microplastics as erosion occurs during water filtration.
Early critics of Plasticroad also argued that the lighter weight of plastic roads will make them permanently unusable for high-traffic areas or roads that must support heavy loads. Eric Kievit, a managing director of Plasticroad, agrees. But the criticism is irrelevant, says Kievit, because that’s not the mission of Plasticroad. The company focuses only on pedestrian pathways, bike paths, and other light-use infrastructure.
The future of the plastic road
So what of the future of plastic roads?
In the near term, plastic asphalt seems like the surer bet. Plastic asphalt is more a refinement of a legacy technology than a replacement. We shouldn’t be surprised that it’s found wider adoption: It’s easier to persuade a city to slightly change their bitumen mix than to upend the 200-year tradition of asphalt.
The future of fully plastic roads like Plasticroad must be far more speculative. While Plasticroad seems to offer long-term cost savings, no projects have existed long enough to validate the promise of decades-longer lifetimes for the roads. Without use as highways and city streets, Plasticroad, too, is unlikely to challenge asphalt’s dominance for major roads.
But Plasticroad might change cities in another way. It makes the infrastructure to support human-scale urban design much cheaper, faster to build, and easier to maintain. If it’s cheaper and easier to make bike paths and footpaths, perhaps cities will build more of them. Even if plastic may not be the future of roads, we need more innovators like the plastic road pioneers working on the problems of our built environment.