When discussing infrastructure sustainability, the risk of remaining too generic is extremely high. Everything is often reduced to an energy or environmental issue, forgetting that a structure is sustainable only if it can maintain over time a real balance between social, economic and environmental benefits and the ability to respond to accidents, degradation and obsolescence.

In the case of road tunnels, this perspective is particularly important. Here, sustainability cannot be separated from safety, and safety cannot be treated as an isolated issue. Tunnels concentrate traffic, energy-intensive systems, complex environmental conditions, operational continuity needs and emergency scenarios that put both design and management under pressure. For this reason, talking about sustainability in this context necessarily also means talking about risk.

Time, degradation and real robustness

An infrastructure ages, degrades and changes its behavior under the effect of use, accidents, stress and technological obsolescence. If all this is treated in a purely deterministic way, as if a structure designed once with adequate safety factors were robust by definition, a dangerous illusion is created. Fragility emerges only after a serious event, when the real margins have already been reduced.

From this perspective, the sustainability of a tunnel can be seen as the ability to react in an asymmetrically positive way to volatility and stress, that is, to achieve over the long term more benefits than damage in socio-economic and environmental terms. It is not enough for the infrastructure to withstand pressure: it must do so while maintaining a positive balance between the service provided, the safety guaranteed, environmental impacts and the overall costs to society.

Risk, therefore, does not concern only traffic or fire. It becomes a cross-cutting key that helps interpret different components of sustainability: human health, economic loss, environmental damage, air quality, resilience of the structure and management uncertainties. In this logic, the opposite of risk is not the absence of danger, but the presence of measurable benefits: greater reliability, lower social costs, better service, reduced environmental impact and higher residual value of the infrastructure.

Energy, safety and system performance

One of the most interesting aspects of this perspective concerns energy. In tunnels, sustainability should not be interpreted as simple consumption reduction, but as the ability to use energy produced from renewable sources to improve service and increase safety.

This means, for example, powering more effective lighting systems or preventive ventilation with photovoltaic energy when potentially dangerous conditions arise. The issue, therefore, is not consuming less at all costs, but making better use of the available energy to reduce overall risk.

The same logic applies to safety systems. Risk-based design and management make it possible to balance the performance of different subsystems more intelligently. An innovative system, if truly effective in reducing risk, can allow a reduction in the performance required from other more energy-intensive systems. This is the case, for example, with automatic extinguishing systems, which can limit temperatures and smoke and therefore reduce, for the same level of risk, the demands placed on the ventilation system.

Here sustainability is not a slogan: it is integrated optimisation between safety, energy and performance.

Environment, costs and long-term vision

There is also an environmental aspect that is often underestimated in tunnels: the concentration of pollutants at the portals. Open-air roads distribute emissions along the route, while tunnels concentrate them at specific points, with possible criticalities especially in urban areas or near homes. The availability of renewable energy could make possible strategies that are currently held back mainly by energy costs, opening the way to management that is more attentive even to the external effects of the structure.

From an economic perspective, increasing environmental sustainability and safety requires higher initial investments, but these must be read in a broader perspective: greater resilience, shorter closure times, lower social and health costs, fewer management uncertainties, higher residual value of the infrastructure, less deterioration of systems and better service for users.

It is a vision opposed to the short-sighted logic of minimum immediate cost: investing better today to avoid much higher economic and social costs tomorrow.

Conclusion

The sustainability of a tunnel cannot be reduced to an energy or environmental formula. It depends on energy, monitoring, fire mitigation, system quality, informed risk management and the ability to read infrastructure as an organism that must remain robust over time. In this sense, risk and sustainability are not separate issues: they are two sides of the same strategy.