In 2021, Pennsylvania mixed plastic equal to about 150,000 shopping bags into 1.5 miles of road at Ridley Creek; later checks found it performing like normal asphalt

A plastic shopping bag usually has a short journey. It carries groceries home, holds household items for a while, and often becomes a difficult waste problem after it is thrown away. However, in Pennsylvania, transportation engineers decided to test whether some of that waste could become part of something people use every day, for instance, a road.

In 2021, engineers used recycled plastic equal to about 150,000 single-use shopping bags in an asphalt mixture for a 1.5-mile road reconstruction project at Ridley Creek State Park. The goal wasn’t just about helping remove plastic from the waste stream. Engineers wanted to find out whether asphalt containing recycled plastic could withstand everyday road conditions as well as regular asphalt. To test this, Pennsylvania transportation officials built the road section as a five-year trial project and continued checking how the pavement performed over time. Thousands of those discarded waste items have found an unconventional second life under traveling vehicles rolling through a state park.

A road built from a waste problem


Plastic waste proves difficult to recycle because many types of plastic are collected together, making processing more complicated. Transportation agencies have been exploring roads as a potential destination since paving projects make use of a great volume of material. In the case of Ridley Creek, PennDOT did not reconstruct the entire road out of plastic, but made use of recycled plastic as an additive in the asphalt. Two sections of the road were treated with this mixture, while other sections remained with conventional asphalt, so that comparative research could be performed. Although the recycled plastic mixture represented a small percentage of asphalt, the volume added was considerable due to the size of the project. The same reconstruction effort also included the reuse of reclaimed asphalt pavement in the new surface.

Testing whether recycled plastic can withstand real roads

Reuse of waste as infrastructure is a good idea, but it’s also important to make sure recycled materials can withstand the field. Roadways are subjected to repeated stresses from vehicles, seasonal weather changes, and rain. Materials that perform well in the lab are not necessarily successful in the outdoors after a few years. The project was a trial rather than a permanent solution. The agency has also commented that recycled products need to be functional and to satisfy practical needs before they can be readily embraced. The availability, quality, and cost are important because transportation projects demand a large and regular supply of material. Another concern associated with plastic-based roads is whether the plastic particles will be released into the environment over time. PennDOT has been monitoring the pavement’s technical performance as well as possible microplastic release during the evaluation period.

Early checks showed the pavement was holding up

The initial results gave engineers a reason to pursue further research of the material. PennDOT reported that the recycled plastic asphalt was performing comparably to conventional asphalt and found no evidence that plastic particles were escaping from the pavement sections being tested. The five-year trial period provided engineers with valuable information about how recycled plastic asphalt performs under real-world conditions. However, continued monitoring remains important because roads are expected to function safely for decades. The demonstration isn't meant to imply that all plastic waste can be used directly in road construction. Rather, it provides data on one specific mixture under real-world conditions.

How the transportation industry is rethinking waste

Roads are one of the few industries that can utilize such large amounts of recycled material. There is a massive need for aggregate and asphalt for each mile of new pavement, and this is a place where materials may be able to find other applications. Transportation agencies nationwide have tested various reclaimed materials such as reclaimed asphalt, concrete, glass, rubber, and plastics. PennDOT recognized a number of potential advantages of using recycled plastic asphalt, such as the reduction of plastic waste disposed of in landfills, the development of markets for recycled materials, and the potential for extending the useful life of asphalt pavements. As part of its own recycling program, PennDOT has also assessed a number of options to determine materials that can be used in an engineered manner.

The growing demand for recycled construction materials

Roads are among the largest consumers of raw materials in the United States. Due to this size, a small change in pavement design can result in a big requirement for recycled material. The challenge for engineers is not only finding a way to reuse waste but also ensuring that recycled materials meet the same safety, durability, and performance standards as traditional materials. Long-term testing, such as the Ridley Creek project, provides the necessary data to make the decision on which of these options can be expanded from the experimental roads to broader applications.