The road to microplastic-free highways

Members of the HTMA's Sustainability Advisory Group discuss the impact of the plastic used in highways management and maintenance

When the BBC's Blue Planet II aired at the end of 2017, it brought home to viewers the devastating impact our use of plastic is having on the environment. Many people watching the programme immediately vowed to cut down on their use of non-recyclable plastics, swearing off takeaway cups and single-use plastic bags in favour of reusable drinking bottles and bags for life.

In many industries, though, such simple switches are just not possible. The highways maintenance sector is one such sector, and the Highways Term Maintenance Association (HTMA) is aware that the issue of plastics needs to be addressed. “It is important that we start looking at the impact highways is having in this area,“ says Jason Convey, senior health, safety, environment and quality manager at VolkerHighways and chair of HTMA's Sustainability Advisory Group. “It is vital that we as a sector look at the way we design our roads and the materials we use in building and repairing our roads. It is an opportunity to invest and innovate ways of reducing the use of plastic to achieve this. It is important that the HTMA lead and facilitate this.“

Last year, HTMA launched a Sustainability Charter aimed at helping the highways management and maintenance industry become more sustainable during the next five years. Among the points set out in the charter is a commitment to address key sustainability challenges, such as plastics consumption.

Material benefits

Plastic is used to make thousands of roadside products that the industry relies on for safety, including cones, barriers, signs and bollards. To a much lesser extent, it also goes into products such as road markings, which can contribute to the release of microplastics into the environment.

“The reason why products like cones and barriers are made out of plastics is because they are resilient,“ explains Malcolm Bryson, Amey Highways health, safety, environment and quality manager for environment and sustainability. “They need to be lightweight so that they are easy to handle, as well as being robust enough to last for a long time. That means plastic might well be the best material for those products.“

The companies that manufacture these products are increasingly finding ways to incorporate recycled plastic into the mix: one manufacturer announced two years ago that it would be using recycled vinyl flooring in the manufacture of its traffic cones. Others, meanwhile, are looking to make the products fully recyclable at the end of their useful life. One advertises that 75% of its products – which include pedestrian and traffic barriers, road plates, signs and cones – are made from recycled plastic.

AECOM associate director Caroline Toplis says that recycled plastics can also be incorporated more directly into highways. “As well as the issues caused by the use of plastics in highways, there are solutions. Innovative work is being done to incorporate waste plastics into highways materials. AECOM has been gathering evidence of projects around the world that are researching the use of plastic waste in asphalt road construction, as part of its work for work for the Midlands Highways Alliance on reducing the carbon impact of highways maintenance activities.“

The microplastic problem

One of the examples Toplis looked at is a trial by Enfield Council to use asphalt that incorporates recycled plastics for road resurfacing. The asphalt contains between 3kg and 10kg of recycled plastic pellets per tonne, with the plastic replacing bitumen in the mix. The London council's trial follows one by Cumbria County Council, which used the same material to resurface a section of the A7 in the Lake District.

However, Bryson advocates caution when it comes to including plastic pellets in the surface layer. “It is a good use for low-level recycled plastics – the mixed dirty plastics like shopping bags – where it can really be put to use rather than burning it. And if you use it in the lower levels of road construction, where it won't wear away, that is great,“ he says. “But my concern is if you put it in the wearing course, that you will create microplastics. One of the significant issues for us is road wear particulates. This has only become a mainstream issue recently, but it's a key challenge for the highways sector.“

Microplastics are small plastic particles, usually classified as anything from 5mm in diameter down to microscopic size. The presence of these microplastics in all sorts of products and waste has recently become a significant topic of debate as their effects on the environment become better understood. We now know that these tiny particles are being ingested by animals and can be embedded in their tissues, as well as getting into the food chain so that humans are also ingesting them.

Microplastics can be formed when larger chunks of plastic are broken down, but they are also manufactured as a raw material for different industries. In January, the UK government banned their use in cosmetics and personal care products such as exfoliating face scrubs and toothpastes.

Industry solutions

Increasing concern and interest in plastics has intensified the amount of research on emissions being carried out internationally. The European Tyre and Rubber Manufacturers Association (ETRMA) has set up a working group to look at the whole body of evidence on tyre and road wear particulates. It is also part of the Global Plastic Release Project, which includes global businesses such as Adidas, Dow and Mars, along with the United Nations Environment Programme, the International Union for Conservation of Nature and the World Business Council for Sustainable Development.

“We, along with our colleagues in Europe, are watching the developments closely,“ says Paul Aldridge, sustainability director at road marking specialist WJ Group. He adds that almost all UK road markings are made using hot applied materials, which, like most surfacing materials, consist principally of aggregates and binder. “The base raw materials for road markings are mainly by-products from other industries. The aggregates come from waste offcuts from marble quarrying, the reflective glass beads are made from recycled glass cullet and most of our binders are bio-based by-products from paper manufacture using natural tree resins. As such, the actual plastics content in road marking materials is extremely low, at 1% or less. Coupled with the fact that all plastic packaging used is melted down to become part of the end product and with the development of significantly more durable products, we are continuing to reduce our impact.“

Again, the industry is looking for solutions, says Bryson: “There is a lot of innovative work going on. While our road marking partners are looking at alternatives to plastics, we have been looking at microplastics associated with brake and tyre wear. There have been some interesting trials using data collection and smart technology.

“Where you get the most wear is at junctions, because of the braking and accelerating. Using cameras and vehicle tracking of HGVs, which have more impact, it is possible to prioritise these vehicles at traffic lights so that they don't have to stop.“ Bryson explains that this technology can be used to create a priority hierarchy at controlled junctions, with emergency services at the top, then buses, and then HGVs. “It's not going to happen overnight, but it is of interest to Highways England and local authorities where there are big challenges around road quality.“

The highways maintenance sector may still be at the early stages of understanding the impact of its use of plastics, but initiatives like these suggest that solutions are available.

The HTMA's Sustainability Advisory Group aims to highlight and tackle sustainability risks that influence the highways management and maintenance industry, and ensure pragmatic delivery of sustainability.