According to WPB, Europe has launched a new research project examining whether asphalt pavements can function not only as transport infrastructure but also as seasonal heat exchangers capable of collecting, transferring, and reusing thermal energy. The TARS — Thermo-Active Roads for Sustainable Heating and Cooling — project began on October 1, 2026, and will continue until September 30, 2028, with the aim of developing a more complete engineering understanding of pavements that contain fluid-carrying pipes within or beneath the asphalt structure.
The basic concept is straightforward but technically demanding. Pipes embedded in the pavement circulate fluid that can absorb part of the heat accumulated by asphalt during warm periods and transfer it for direct use or storage. During colder periods, the same network can return heat to the pavement, creating a two-way thermal system rather than leaving the road as a passive surface exposed only to natural temperature cycles. In practical terms, the road becomes both a structural asset and a thermal interface.
The idea is particularly relevant because asphalt naturally absorbs large amounts of solar radiation. During summer, dark pavement surfaces can reach very high temperatures, increasing the thermal load on the pavement and potentially contributing to temperature-related deformation and faster material aging. A thermo-active system attempts to turn part of this thermal burden into a usable energy resource by removing heat before it remains trapped in the pavement or is released back into the surrounding environment.
Reducing summer pavement temperature could provide a second benefit beyond energy collection. Lower peak temperatures inside asphalt layers may reduce susceptibility to some heat-related damage mechanisms and could potentially improve long-term durability. The reverse process may also be useful during colder conditions, when stored or externally supplied heat can circulate through the embedded pipes and raise pavement temperature. However, the project is not presenting a finished commercial snow-melting or road-heating system; its purpose is to determine whether the concept can operate reliably over the full structural life of a road.
The project is coordinated by École Nationale des Ponts et Chaussées in France, with Université Gustave Eiffel and Imperial College London participating as partner institutions. It is supported through the Marie Skłodowska-Curie Actions program under Horizon Europe, with an EU contribution of approximately €242,261. The program should therefore be understood as a focused research project rather than the beginning of large-scale installation of heated and cooled roads across Europe.
This distinction is important because the central challenge is not simply whether heat can be transferred through asphalt. Earlier research has already demonstrated that circulating fluid through embedded pipes can collect thermal energy or warm pavement surfaces. The more difficult question is whether such a system can remain mechanically durable while repeatedly carrying traffic loads, experiencing seasonal temperature changes, and operating as an energy system over many years.
Embedding pipes changes the internal structure of a pavement. The pipes create new interfaces and can alter local stiffness, temperature gradients, and stress distribution, all of which may affect how asphalt responds to repeated vehicle loading. A system could perform extremely well from a thermal perspective and still be unsuitable for road use if the pipe layout creates cracking, deformation, or weak zones within the pavement. For this reason, TARS is developing a coupled thermo-mechanical framework rather than treating heat transfer and pavement mechanics as separate problems.
This combined approach is especially relevant to asphalt because binder behavior is strongly temperature-dependent. As temperature rises, the binder becomes softer and the risk of permanent deformation can increase; at lower temperatures, it becomes stiffer and may become more vulnerable to thermal cracking. Removing or adding heat therefore changes more than the surface temperature of the road. It can also change the mechanical state of the asphalt layers themselves, which means thermal performance and structural durability must be assessed together.
The research will combine multi-physics and multi-scale modeling, pavement characterization, laboratory testing, and numerical simulation. One of the objectives is also to create a surrogate metamodel that can estimate long-term thermal performance without requiring the full computational cost of detailed simulations for every possible operating condition. Such a model could eventually allow engineers to examine variables including pipe depth, spacing, fluid temperature, flow rate, climate, and pavement composition in a more efficient way.
These design variables create a series of engineering trade-offs. Pipes placed close to the surface may collect heat more efficiently because they are nearer to the hottest asphalt layers, but shallow installation can expose them to greater mechanical stress from traffic and construction operations. Deeper pipes may be better protected structurally but could reduce thermal-transfer efficiency. A denser pipe network may improve heat exchange while also increasing material use, installation cost, maintenance requirements, and the number of interfaces inside the pavement.
The project therefore treats thermo-active roads as integrated pavement–energy systems rather than simply conventional asphalt containing heating pipes. The temperature of the circulating fluid, the intensity of heat extraction, and the resulting thermal gradients must all remain compatible with the mechanical behavior of the pavement. Extracting more energy is not necessarily beneficial if it creates thermal or structural conditions that shorten the road’s service life.
A major part of the research is also devoted to cradle-to-grave life-cycle assessment. This is essential because a pavement cannot be considered sustainable only because it collects renewable heat. The environmental cost of manufacturing and installing the pipe network, running pumps, storing thermal energy, maintaining the system, and eventually reconstructing the pavement must also be included. If installation significantly increases construction impacts or reduces pavement life, part of the energy benefit could be canceled out.
The reverse is also possible. If active thermal regulation reduces damaging temperature peaks, extends pavement life, or lowers winter-maintenance requirements, the environmental and economic benefits may become substantially larger than the value of harvested heat alone. This interaction between energy collection and pavement durability is one of the most commercially significant aspects of the concept because road infrastructure already covers an enormous surface area that exists primarily for transportation. If part of that area can also function as thermal infrastructure without compromising road performance, the same physical asset could perform two functions.
Unlike photovoltaic systems, thermo-active roads are not primarily intended to convert sunlight into electricity. They operate as thermal collectors: asphalt absorbs solar energy, the pipe network transfers heat into circulating fluid, and that energy can then be used directly or stored for later use. Low-temperature thermal energy may be suitable for several applications, but the current project has not demonstrated that a given road can economically heat a defined number of homes or buildings. Any such claim would depend on pavement area, climate, storage technology, system losses, operating temperature, and the actual thermal demand of the connected user.
For that reason, the immediate goal of TARS is more fundamental than the idea of roads heating buildings. The project is trying to establish whether a thermo-active pavement can provide useful thermal energy while remaining mechanically durable and environmentally sustainable over its full life cycle. If that technical foundation can be demonstrated, future projects could then evaluate specific commercial applications.
Long-term behavior will be critical because asphalt properties change with age. Oxidation gradually stiffens the binder, while the embedded pipes and their surrounding interfaces may experience repeated expansion and contraction as temperatures change. A system that performs efficiently in a short laboratory trial may behave very differently after years of traffic loading, binder aging, and seasonal thermal operation. The road must therefore maintain both structural and thermal performance throughout its service life.
This gives the project direct relevance to the bitumen industry. If thermo-active pavements progress toward wider deployment, binders may eventually need to be evaluated not only for conventional traffic, water, and climate exposure but also for repeated thermal cycles created by the energy system itself. Binder rheology could become an increasingly important design parameter because actively controlled pavement temperatures may create thermal histories that differ significantly from those of conventional roads.
Polymer-modified bitumen could become relevant where greater resistance to deformation or repeated thermal cycling is required, although the project does not currently establish that polymer modification is necessary. The appropriate binder would depend on pavement structure, climate, pipe configuration, and operating temperature. The same principle applies to asphalt-mixture design because aggregate structure, air voids, layer thickness, thermal conductivity, and binder characteristics could all affect both heat transfer and structural response.
This could eventually introduce new performance criteria into asphalt specifications. Conventional pavement design focuses primarily on resistance to traffic loading, cracking, rutting, moisture, and aging, while an energy-active pavement would add another requirement: the ability to exchange heat efficiently without sacrificing those conventional properties. That could create new research opportunities in bitumen formulation, thermally conductive aggregates, recycled materials, and additives designed specifically for thermo-active roads.
Construction practices would also need to adapt. Pipe position and depth would have to remain accurate during paving and compaction, while the system itself would need to tolerate asphalt production temperatures, roller loads, and later maintenance operations. Future milling or rehabilitation would become more complex because contractors would have to account for embedded infrastructure beneath the pavement surface.
The concept may also have implications for urban heat management. Removing part of the energy stored in asphalt during peak summer periods could reduce surface temperature and potentially lower the amount of heat released back into the urban environment. The actual magnitude of that effect will depend on local climate, system size, and operating strategy, and the project still needs to validate whether the benefit is significant enough to matter at a practical scale.
From a commercial perspective, the decisive question will eventually be whether the value of recovered energy and any extension of pavement life can justify the additional construction, maintenance, and operating costs. A technically successful system is not automatically an economically competitive one. Energy prices, installation costs, thermal storage, maintenance complexity, and rehabilitation schedules will determine whether thermo-active roads can move beyond research projects into routine infrastructure.
TARS will continue until September 30, 2028, and its most important outcome may not be a road that literally heats and cools on command, but a validated engineering framework showing where such systems make technical and environmental sense. For the asphalt and bitumen industries, that alone would represent an important change in how pavement is viewed: not only as a structure that must survive heat, but potentially as infrastructure capable of collecting, moving, and reusing it.
By WPB
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