Pennsylvania used 5,570 tons of shredded tires in the Tarrtown Bridge approaches; project estimated to save about $514,000

Waste tires accumulate quickly. An estimated one billion waste tires are generated around the world each year, while the United States generates approximately 240 million to 250 million annually, according to a 2026 review published in Transportation Infrastructure Geotechnology. The figures highlight the scale of a waste stream that can create storage, disposal, and fire-management challenges. Instead of sending some of those tires toward conventional disposal, engineers in Pennsylvania used processed tire material as part of a bridge construction project.

At the Tarrtown Bridge project on Tarrtown Road in Armstrong County, Pennsylvania, crews used tire-derived aggregate as lightweight fill in the bridge's two approach embankments. The aggregate consisted of processed, angular tire shreds, and the project used approximately 5,570 tons of the material, equivalent to roughly 557,000 tires. PennDOT monitored settlement and structural behaviour during and after construction, with the project demonstrating how the lightweight material could be used to address difficult ground conditions.

Why shredded tires can work as fill


The main advantage comes down to weight. Conventional soil and rock fill can place substantial pressure on weak ground beneath a road or bridge approach. That pressure can contribute to settlement, which is particularly troublesome where a bridge structure meets an earth embankment. The bridge itself is relatively rigid, while the surrounding ground can move and settle differently.

Tire-derived aggregate offers a much lighter alternative. The 2026 review by Belay Nerea and colleagues describes TDA as a lightweight material that can reduce vertical and lateral stresses on underlying soils. That makes it useful in applications such as embankments, retaining walls, and other structures where the weight of conventional fill could be a concern.

The material also has a useful physical characteristic that may seem surprising for something made from old tires: it allows water to move through it readily. The spaces between the tire shreds give TDA relatively high permeability, allowing it to function as a drainage material as well as lightweight fill. Good drainage can be valuable around roads and bridges because trapped water can weaken surrounding soil and contribute to problems associated with repeated wetting, freezing, and thawing.

At Tarrtown, the lightweight fill was particularly useful because the approach embankments were being constructed over ground where reducing the load was important. PennDOT's project documentation compared the tire-derived aggregate approach with conventional excavation and replacement methods. Its cost analysis estimated that the TDA approach could save about $514,000 compared with the conventional alternative. That figure is a projected cost difference from the project's analysis, rather than a claim that exactly $514,000 was ultimately paid out as a cash saving.

From waste tires to infrastructure

Tire-derived aggregate is not limited to bridge approaches. The 2026 review notes that processed tires have been used in embankments, retaining walls, drainage applications, and other civil engineering projects. Depending on how the material is processed and where it is being used, engineers can select different particle sizes and configurations to provide the required combination of strength, drainage and weight reduction.

Its lightweight nature can also reduce the pressure placed on retaining structures and underlying soils. In cold regions, tire-derived aggregate has additionally been investigated for applications where its properties can help limit frost-related problems.

There is an environmental consideration, however. Turning tires into construction material does not mean the material can be used indiscriminately. The review found that research generally indicates a low risk to groundwater from TDA leachate, but some short- and long-term studies have reported elevated concentrations of elements such as zinc and iron. That means engineers still need to consider local soil, groundwater, and drainage conditions before selecting tire-derived aggregate for a particular project.

Using old tires in infrastructure can nevertheless help address one of the problems created by stockpiling them. The U.S. Environmental Protection Agency has noted that large tire piles can collect rainwater, creating potential mosquito-breeding habitat, while also presenting significant fire risks. Finding productive applications for processed tires therefore provides an alternative to simply storing or disposing of them.

The Tarrtown project shows how an awkward waste stream can become a practical engineering resource. By using lightweight tire-derived aggregate in the bridge's approach embankments, Pennsylvania engineers were able to reduce the weight placed on the underlying ground while putting hundreds of thousands of waste tires to work in infrastructure.