In a creative engineering project in 1995, 20,000 discarded tyres were buried beneath a road in the US state of Maine to solve two problems at once: winter frost and spring mud. The trial was documented in a paper titled Field Performance of Tire Chips as Subgrade Insulation for Rural Roads. The paper describes the use of tyre chips as an insulating layer to limit frost penetration beneath a gravel-surfaced road.
The project was significant because Maine has a large network of gravel roads that face a brutal seasonal cycle. In winter, frost penetrates deep into the ground. In spring, that frozen ground thaws, holding water and turning soft and unstable. Heavy vehicles then leave deep ruts, potholes and mud that make roads almost impassable.
At the same time, Maine generated more than a million scrap tyres every year, with hundreds of illegal stockpiles reported in the early 1990s. Tyres take a very long time to break down, occupy valuable space in landfills and pose fire and pollution risks. Finding a safe, large-scale outlet for them had been a persistent challenge.
Then an idea came from University of Maine civil engineer Dana N. Humphrey. Instead of using whole tyres, his team cut them into large chips (typically 12mm to 76mm) and placed them beneath the road surface to create a thick, lightweight layer.
This layer improved drainage and reduced the effects of freezing and thawing. In cold regions, water in the soil freezes during winter, causing the ground to expand and push the road upward. When temperatures rise, the frozen ground melts and becomes soft and muddy. This repeated cycle causes cracks, potholes and uneven surfaces. The buried tyres helped create a flexible and well-drained foundation.
Their shape created voids where water could move instead of remaining trapped in the soil, allowing the road to better handle changing weather conditions. The project also demonstrated an environmentally friendly way to reuse waste. Instead of sending thousands of old tyres to landfills, engineers gave them a second life as useful infrastructure.
EPA’s 2003 report “Recycled Rubber Raises the Road | Maine Bridge Rehabilitation” also described the project that used the shredded tyres to raise a road and save $8.7 million over traditional methods
Why rubber?
Tyre chips are lightweight, highly permeable like coarse gravel and have excellent thermal insulation properties. They resist frost penetration and drain water away during the spring thaw. In the 1995 field trials, sections built with tyre chips showed noticeably less frost penetration and deterioration than adjacent conventional sections.
The approach is now known as Tyre-Derived Aggregate, or TDA. Federal highway guidance notes that tyre shreds offer reduced unit weight, good thermal resistance and good drainage, making them especially useful over weak soils and in cold climates.
Environmental studies by Humphrey found that when placed above the water table, tyre chips had negligible impact on water quality, with reviews concluding TDA has limited effect on drinking water quality when used as insulation and drainage layers beneath roads.
