Energy Transition of Road Infrastructures: Analysis of the Photovoltaic Potential on the A3 Napoli–Pompei–Salerno Highway

Abstract

The energy transition of the road transport sector is now a strategic priority for achieving global decarbonization targets. In particular, the highway sector offers the opportunity to integrate sustainable solutions without additional land consumption, thanks to the availability of relevant areas that are already covered by infrastructure. This study proposes a large-scale analysis of the potential photoelectric energy that can be produced within highway infrastructures, with the aim of evaluating the contribution that these assets can make to electric mobility. The analysis was conducted using geographic information systems (GISs), applied to the case study of the A3 Napoli–Pompei–Salerno highway. The processing of topographical, orographic, and solar data has made it possible to identify a total surface area of approximately 27,100 m² that is potentially suitable for the installation of photovoltaic systems, distributed among service areas, toll stations, car parks, and side sections. This result highlights the concrete possibility of making the most of the energy potential of highway infrastructure, promoting self-production and local consumption models to power the electric vehicle charging network, thus contributing directly to the reduction of emissions and the sustainability of the transport system.

1. Introduction

The growing recognition of the impact of greenhouse gas emissions on the global climate crisis has catalyzed international efforts to mitigate the environmental consequences through key agreements and initiatives. The 1997 Kyoto Protocol marked one of the first formal attempts to engage developed countries in binding commitments to reduce emissions [1]. Although a pioneering step, the Protocol faced several challenges, such as limited participation and the absence of commitments for developing countries, which undermined its overall effectiveness. A subsequent global commitment was made in 2015 with the Paris Agreement, which introduced a more comprehensive and flexible framework, stipulating that each participating country should set voluntary national emission reduction targets, while promoting accountability and financial support for developing countries [2]. The main goal of the agreement was to limit global warming to less than 2 °C above pre-industrial levels, with a further commitment to a more ambitious target of 1.5 °C. However, current emissions trajectories indicate that we are on course for significantly higher temperature increases, with possible scenarios of extreme weather by the end of the century [3]. The role of international financial mechanisms, such as the Green Climate Fund, has become fundamental in this context [4]. These mechanisms are essential for financing projects aimed at both reducing emissions and adapting to unavoidable climate change. Regional and bilateral agreements have broadened the scope of mitigation strategies, allowing for a more targeted approach and effective exchange of technology and experience between countries. An in-depth analysis of greenhouse gas emissions into the atmosphere needs to recognize the contribution of each sector. Sectors such as transport, agriculture, waste management, and industry play different and significant roles in this landscape. For example, the transport sector emits significant amounts of CO₂, N₂O, and CH₄ through the use of fossil fuels [5]. The waste sector produces GHGs from the decomposition of organic waste and its incineration, while buildings emit CO₂ from energy use and CH₄ from natural gas heating systems [6,7]. Agriculture is a major emitter of CH₄ and N₂O from livestock and fertilizer use, respectively [8]. A detailed understanding of these contributions is essential to formulate effective mitigation strategies and to move towards more sustainable development (Figure 1).

Some countries have adopted particularly effective approaches that not only aim to meet the objectives of the international agreements mentioned above but also provide concrete examples of how energy transition can be successfully achieved. Sweden stands out as one of the leaders in this field, having successfully integrated renewable energy sources into its energy mix [10]. In addition, the country has actively promoted the use of electric vehicles and encouraged consumers to switch from fossil fuels to less fossil fuel-dependent options. These efforts have resulted in a significant reduction in GHG emissions, demonstrating the effectiveness of renewable energy-focused policies. Similarly, Costa Rica has made great strides in promoting renewable energy. This Central American country has achieved almost 100% of its energy production from renewable sources, including hydropower, solar, and wind, positioning itself as a virtuous model of energy transition [11]. Costa Rica’s commitment to a fossil fuel-free economy highlights its pioneering role in the fight against climate change. Denmark has invested heavily in wind energy, becoming one of the world’s largest producers. The Danish approach also includes the development of efficient energy technologies and the promotion of energy consumption from renewable sources [12]. The experience of these countries shows that the benefits of such policies go beyond reducing emissions and also contribute to economic growth and long-term improvements in public health.

The responsibility to preserve the planet for future generations is a global one that requires constant cooperation and sharing of knowledge between countries and organizations. Only through joint and focused efforts can we try to ensure a better existence for all.

According to the International Renewable Energy Agency (IRENA) [13], an effective environmental transition that addresses climate change and improves energy security requires an energy system that not only reduces carbon emissions but also supports a resilient and inclusive global economy. In this perspective, planning must go beyond technological boundaries to address the broader needs of the new energy system and the economies it is intended to support. To achieve this goal, three fundamental pillars have been identified that will need to be addressed over the next thirty years, i.e., physical infrastructure, policy and regulatory frameworks, and skills and capabilities:

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Physical infrastructure: Forward-looking planning is essential to modernize and expand support infrastructure on land and at sea. This pillar includes the development of networks capable of facilitating the generation, storage, distribution, transmission, and consumption of renewable energy. Adequate infrastructure is essential to support national, regional, and global energy strategies and to manage new supply and demand dynamics;

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Policy and regulatory frameworks: It is essential to develop policy and regulatory frameworks that facilitate the deployment and integration of renewable energy and promote energy trade. These frameworks must improve socio-economic and environmental outcomes and promote equity and inclusion. They must enable an effective energy transition at all levels, from local to global, and adapt to new energy supply and demand dynamics;

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Skills and capabilities: It is essential to raise awareness and strengthen the capacity of institutions, communities, and individuals to acquire the skills, knowledge, and experience needed to drive and support the energy transition. Digitization offers many opportunities that can be harnessed for policies that enhance social sustainability.

The forecast for total primary energy supply is expected to remain stable due to increased energy efficiency and growth in renewable energy. The share of renewables in primary energy supply is projected to increase from 16% in 2020 to 77% in 2050 [14]. This 61 percentage point increase will be driven by a combination of end-use electrification, renewable fuels, and direct use of renewable energy. Achieving this level of renewable energy penetration is essential to meet global climate goals and will require significant investment, policy support, and continued technological innovation [14].

Improvements in energy intensity will be the result of a combination of renewable and efficient technologies in end-use sectors, together with widespread electrification. Electricity demand is projected to triple by 2050, with 37% of electricity coming from solar and 36% from wind [14]. These projections highlight the scale and complexity of the transformation required for a sustainable energy future.

1.1. Transport Sector

Mobility, both passenger and freight, plays a crucial role in the modern economy and society. In 2024, the transport sector was a significant contributor to global emissions, releasing 8.7 GtCO₂-eq, or about 15% of global energy-related CO₂ emissions [15]. In particular, road transport accounted for more than three-quarters of the sector’s energy consumption, followed by maritime, air, and rail transport [16]. Given the projected increase in demand for transport services, it is essential to promote a transformation of the sector towards sustainable practices in order to reduce carbon emissions. Current projections suggest that the transport sector could undergo a rapid and significant transformation [17]. This scenario envisages a dramatic reduction in the sector’s CO₂ emissions to 0.6 GtCO₂ per year by 2050 [17]. This reduction would represent a 91% difference compared to 2020. Proposed strategies include the large-scale deployment of low-carbon solutions such as electrification of transport, increased use of renewable fuels such as biofuels, hydrogen, and derived fuels, and implementation of energy efficiency measures and technological innovation across all transport modes.

Decarbonizing the transport sector will require the widespread use of renewable fuels, including sustainable biofuels, hydrogen, and synthetic fuels. The production of sustainable liquid biofuels will need to increase 3.3-fold from current levels by 2050, accounting for 23% of the sector’s final energy consumption [18]. The aviation sector would be responsible for 39% of this consumption, followed by maritime transport with 31% and road transport with 30% [18]. The global hydrogen stock would account for 17% of the sector’s energy consumption by 2050, with road transport contributing mainly through heavy-duty trucks [18]. In international shipping, a diversification of low-emission fuels is expected, with ammonia, methanol, and hydrogen accounting for around 72% of the fuel mix by 2050 [18]. In aviation, the use of synthetic kerosene would increase significantly, accounting for 42% of total energy consumption [18].

These changes highlight the need for a transition to an environmentally sustainable transport system that drastically reduces carbon emissions and contributes significantly to the fight against climate change. The key performance indicators (KPIs) used to analyze the transport sector refer to the IRENA 1.5 °C scenario (

Table 1. Key performance indicators in 1.5 °C scenario [19].

			Recent Years	2030		2050
			2020	PES	1.5 °C Scenario	PES	1.5 °C Scenario
KPI.01 Renewables (power)	Electricity generation [TWh/yr]	Global	7468	16,504	27,358	38,118	82,148
		G20	6327	14,269	22,397	31,071	60,547
	Renewable energy share in electricity generation [%]	Global	28	46	68	73	91
		G20	28	48	69	74	91
KPI.02 Renewable (direct use)	Renewable energy share in TFEC [%]	Global	18	23	35	33	82
		G20	16	22	36	35	82
	Modern use of energy [EJ]	Global	21	30	50	41	64
		G20	19	26	36	33	42
KPI.03 Energy intensity	Energy intensity improvement rate [%]	Global	1.7	1.8	3.3	2.0	2.8
		G20	2.1	2.1	3.6	2.3	3.1
KPI.04 Electrification in end-use sectors (direct)	Electrification rate in TFEC [%]	Global	22	23	29	28	51
		G20	25	26	31	32	55
KPI.05 Clean hydrogen and derivatives	Production of clean hydrogen [Mt/yr]	Global	0.7	2	125	21	523
		G20	0.5	2	94	20	373
KPI.06 CCS, BECCS, and others	CO2 captured from CCS, BECCS, and other removal measures [Gt/yr]	Global	0.04	0.1	2.2	0.5	7.0
		G20	0.03	0.1	2.1	0.4	4.9

).

These reflect the ambitious commitment required from researchers, politicians, entrepreneurs, and citizens over the next thirty years, and envisage intensified electrification of transport, greater fuel diversification, and increased deployment of hydrogen-based technologies. At the same time, the development of electric charging infrastructure is one of the main indicators for assessing the feasibility of the proposed targets. These indicators will be selected in line with risk management analyses and will contribute, together with other parameters, to the implementation of effective policies and the realization of projects necessary for the transition to a sustainable transport system.

1.2. Road Infrastructure

Focusing on emissions from the transport sector, the European Union has set significant greenhouse gas emission reduction targets: a 60% reduction by 2050 compared to 1990 levels and a 20% reduction by 2030 compared to 2008 levels [20]. The increase in car emissions is mainly due to the growing market share of sport utility vehicles (SUVs) [21]. In this regulatory context, an emission limit for battery electric vehicles (BEVs) has been set at 93.6 gCO₂/km from 1 January 2025, decreasing to 49.5 gCO₂/km by 2030 and reaching zero emissions by 2035 [22]. This transition to zero-emission vehicles is in line with the broader goal of transforming the continent into a hub for sustainable and low-impact mobility. The path to these goals includes technological improvements and a restructuring of the supporting infrastructure, such as more widespread charging stations and integrated renewable energy systems. These initiatives will be supported by fiscal policies that incentivize the purchase of electric vehicles and regulations that will gradually phase out the production of internal combustion vehicles.

The automotive industry has responded by expanding the electric vehicle market, adapting to technological and environmental needs, and minimizing pollution through the use of clean and renewable energy. These vehicles help to reduce harmful emissions and noise, promote a circular economy, and improve public health. The increasing adoption of electric cars in Europe has stimulated scientific research to assess their impact on the electricity grid and emissions, using mathematical models to analyze their evolution and environmental impact [23]. The analysis of electric car penetration scenarios, with projections of 50% and 80% coverage of the vehicle fleet by 2050, shows positive effects on the reduction of air pollutants [24]. However, potential challenges also arise in terms of electricity grid management and the composition of the national energy mix. A critical issue in these scenarios is the transformation of load curves, i.e., energy losses during transmission and distribution can increase demand in areas with limited energy resources, posing a significant challenge to the sustainability of the grid [25].

In the context of the development of increasingly accurate and common performance indicators (KPIs), derived from extensive experimentation involving multiple actors from different disciplines, converging results have emerged through the application of two different forecasting methods (Table 2). Despite the recognition of the value of the research methodology and the clarity of the presentation, there is a persistent lack of available data, a shortcoming that also limits the present research. The pace of change in data structures is not keeping pace with technological evolution, creating a dead end that hinders the progress of digital research. The models used to analyze the penetration of electric vehicles are based on official data provided by the European Alternative Fuels Observatory (EAFO) (Figure 2).

Despite the representativeness of EAFO, the lack of accessibility, reliability, consistency, and regularity of information updates limits its ability to effectively support research. It is therefore desirable to provide a single official source of useful, easily accessible, and up-to-date data to improve the efficiency of both the research itself and the product comparison. In addition, studies show that while BEVs will reduce greenhouse gas emissions in most EU countries, in a minority of countries, they will not reduce emissions due to their fossil fuel-based energy mix [27].

Table 2. Penetration of BEVs in the EU [28].

Methods	BEV Penetration (2030)	BEV Penetration (2050)	Energy Requirement (2030–2050) [MWh]	Emissions Trend
Linear regression	3.98%	15.98%	90,000.000	Increase until 2034, then a significant reduction
Brown	4.00%	15.50%	87,000.000	Increase until 2034, then a significant reduction, negative values from 2048

Table 2. Penetration of BEVs in the EU [28].

Methods	BEV Penetration (2030)	BEV Penetration (2050)	Energy Requirement (2030–2050) [MWh]	Emissions Trend
Linear regression	3.98%	15.98%	90,000.000	Increase until 2034, then a significant reduction
Brown	4.00%	15.50%	87,000.000	Increase until 2034, then a significant reduction, negative values from 2048

According to [28], model-based projections show that the increasing penetration of electric vehicles in the European market could lead to an initial increase in CO₂ equivalent emissions by 2027 and, in a second scenario, by 2034. This increase is due to current energy production methods. However, these emissions are expected to decline thereafter, driven by investment in renewable energy. These projections highlight the importance of an investment strategy that is closely aligned with policies to support the electric vehicle market. Furthermore, it is essential that this strategy is supported by the implementation of advanced technologies and methods for the digitalization of transport infrastructure, such as those discussed in this paper. This approach could minimize environmental impacts while maximizing the effectiveness of investments and benefiting from increasingly advanced, digital, and high-performance construction management practices.

The aim of the research is to propose a framework to support the transition to electric transport and the creation of intelligent roads. In particular, the paper proposes a large-scale analysis of the photoelectric potential that can be generated in the areas surrounding highway infrastructure, promoting the concept of self-production to support the electricity consumption of heavy and light vehicle traffic, thus avoiding further land consumption.

2. Materials and Methods

The following outlines the proposed methodology for carrying out a large-scale analysis of the photovoltaic (PV) potential that can be generated within the areas surrounding highway infrastructure. The proposal has been developed for the highway sector, as this environment offers several advantages over the rest of the road network.

The Italian territory, a peninsula jutting out into the Mediterranean Sea and including its two largest islands, Sicily and Sardinia, is physically connected to the European continent by the Alps, which form its natural border with neighboring countries. With the exception of a few flat areas, including the vast Po Valley, the country’s morphology is predominantly mountainous and hilly, with an orographic pattern that runs from north to south, creating a complex territorial context in terms of connectivity. This conformation has made it necessary to build a considerable number of bridges and tunnels, both in the road and rail systems. From an administrative and management point of view, the Italian road and highway network is essentially divided into four types of operators for a total of 840,000 km of infrastructure and 8055 operators (

Table 3. National road and highway transport network system [29].

Type of Management	N° of Management Entity	km of Routes	Incidence [%]
Highway concessionaires	27	8006	0.95
ANAS public roads	1	27,259	3.25
Regions, provinces, and metropolitan cities	123	135,691	16.16
Municipalities	7904	668,673	79.64

) [29].

Among these, the highway concessionaires and the national operator ANAS, which have reached a high level of managerial and technological maturity, are well placed to promote the gradual digitization of the infrastructure. The degree of process engineering associated with this type of infrastructure favors change management aimed at creating a networked system for managing public infrastructure assets, bearing in mind that these concessionaires manage 3.25% of the road network (Table 3).

2.1. Integrated System for Energy Sustainability in Highway Transport

The research uses the national highway network as a reference infrastructure to propose a digital framework capable of maximizing and accelerating energy and environmental sustainability plans for road transport. One of the most pressing issues currently hindering the widespread adoption of electric vehicles appears to be the lack of an adequate number of charging points. The advantage of choosing highways is that it guarantees the possibility of installing a satisfactory number of charging points on long-distance routes. Other advantages include the fact that their special concessionary status means that their economic viability is linked to tolls; the possibility of controlling traffic by means of entry and exit barriers; and the presence of service areas and ancillary facilities adjacent to the road platform, which facilitate the installation of renewable energy production systems on the latter, thus avoiding further land consumption. It has been repeatedly demonstrated that the level of digitalization applied to infrastructure assets can manage complex and dynamic systems, which helps to define the complexity of a smart road and smart grid system, where electric vehicles communicate with charging points, which in turn are connected to electricity storage and production systems [30,31,32].

A multidisciplinary and multi-level approach is needed, including regulatory measures, data collection, definition of guidelines, establishment of criteria and incentives, promotion of cooperation between the various stakeholders, and implementation of strategies for defining and financing sustainable investments, and a national control room capable of implementing and managing a just transition.

In order to analyze the potential photoelectric energy that can be generated, seven main hypotheses of a logical, economic, and administrative nature have been put forward, on the basis of which the following proposal has been developed:

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Regulations;

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Data collection;

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Guidelines;

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Criteria and incentives;

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Cooperation;

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Definition and financing;

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Adoption of lean construction protocols.

Regulations: It is important to ensure that sustainable practices in the highway sector are not only encouraged but also mandatory; this may include regulations on greenhouse gas emissions, energy efficiency standards for vehicles, and requirements for the use of renewable fuels. This is similar to the provisions for the PNRR and Recovery and Resilience Facility (RRF) funds, or for EU-funded projects under the European Green Deal. The process can be based on the Do No Significant Harm (DNSH) principle implemented by Regulation (EU) 2020/852 and complemented by Commission Delegated Regulation (EU) 2021/2139 of 4 June 2021.

Data collection: The core of the analysis is also based on effective and accurate data collection, which is essential for monitoring the environmental impact of highway transport and for assessing the effectiveness of the policies implemented, thus allowing a control room to follow every step of the creation and management of a sustainable and environmentally friendly transport system, while at the same time leaving individual implementers free to manage their own changes in compliance with the regulations in force. This can include data on traffic, fuel consumption, CO₂ emissions, the use of electric vehicles, the efficiency of renewable energy production facilities, and much more. By analogy with the processes of digitization and regulation of information flows for the design, construction, and management of road works, an appropriate ontology aimed at the energy sustainability of electric transport can be devised. By standardizing the information content and integrating it into the IFC 4.3 standard, the sustainability of road and highway corridors can be extended well beyond national borders, reaching first and foremost the TEN-T network [33].

Guidelines: Provide companies and government agencies with guidance on how to implement sustainable practices. These can cover various aspects such as environmentally friendly highway design, sustainable maintenance, and the use of sustainable technologies.

Criteria and incentives: Setting clear criteria and offering financial incentives can motivate both companies and individuals to make more sustainable choices. Incentives can include subsidies for the purchase of electric vehicles, tax breaks for companies that adopt sustainable practices, and funding for research and development of sustainable technologies. The choice of highway assets provides another opportunity to incentivize investment through a share of highway toll revenues.

Cooperation: Cooperation between the public sector, the private sector, non-governmental organizations, and civil society is essential to promote sustainability in the highway sector. Through partnerships and joint projects, knowledge, resources, and best practices can be shared.

Definition and financing: It is important to clearly define sustainability goals and ensure adequate funding to achieve them. This may include investment in sustainable infrastructure, such as charging points for electric vehicles and improvements to the energy efficiency of highways. Equally important is investment in a governance structure capable of coordinating and monitoring the whole system, while promoting innovation and sustainability within the principles of the well-known Deming cycle: Plan–Do–Check–Act [34].

Adoption of lean construction protocols: For the management and optimization of civil engineering and plant and infrastructure projects, with the aim of reducing waste, improving efficiency, and optimizing processes within a construction site, with the aim of delivering the project with the best possible use of resources, faster timescales, and higher quality.

Addressing the energy sustainability of road transport requires long-term commitment and cooperation from all stakeholders. With robust regulations, appropriate incentives, and a shared commitment to sustainability goals, it is possible to achieve a more efficient and sustainable highway transport system.

2.2. Analysis of Elements for the Development of the Framework

In the context of analyzing the energy potential of highway infrastructure, it is essential to outline the role of the actors involved. Governments and regulatory authorities play a central role in defining the rules and standards for data collection and ensuring that it is carried out in a uniform, consistent, and systematic manner. At the same time, highway operators are responsible for collecting and analyzing traffic data to monitor traffic flow conditions and identify critical issues or infrastructure needs in a timely manner. To complete this ecosystem, end-users, i.e., vehicle drivers, also contribute to the generation of useful data through their daily mobility activities.

In order to estimate the energy requirements associated with electric mobility on highways, a calculation model has been developed to quantify the total energy consumption required to support the circulation of electric vehicles. The simplified model adopted is intended as a preliminary tool to obtain an initial estimate to support the subsequent phase of assessing the technical and economic feasibility of the intervention. The construction of more complex simulation models, capable of integrating real-time traffic information and providing a dynamic view of the system, will be the subject of future studies.

Another important aspect is the assessment of the potential of renewable energies in the highway sector. Identifying and mapping the areas available for the installation of PV systems and other renewable technologies along the highway route are crucial activities to respond sustainably to the energy demand generated by electric mobility. This methodological approach represents a paradigm shift in the design of highway infrastructure: from passive elements that have historically occupied significant areas of land, they are transformed into active and productive players from an energy point of view. In this way, part of the land taken from the natural landscape can be symbolically returned to the community through the production of clean energy.

The next phase of the analysis concerns the integration of energy supply and demand through the simulation of energy scenarios and the development of storage strategies. In a transitional phase such as the current one, it is necessary to consider different levels of penetration of electric vehicles and to plan the distribution and timing of the installation of production facilities in a coherent manner. If properly managed, the balance between renewable energy production and vehicle consumption can not only meet local demand but also export excess energy to the national grid or industrial districts. Planning is an essential step in ensuring the effective implementation of support infrastructure, whether through new construction or adaptation of existing facilities. This must be accompanied by continuous monitoring and regular updating of the system to adapt to changes in energy demand and technological innovation.

3. Case Study of the A3 Naples–Pompei–Salerno Highway

The Naples–Pompei–Salerno highway was built on 21 May 1925 and opened in June 1929 (Figure 3). It was the second highway in Italy after the Milan–Laghi highway. In the years that followed, work on the highway was interrupted by the Second World War but was resumed at full speed during the economic boom. The infrastructure continued to develop until the 2000s, when major upgrades were carried out, including technological improvements to increase the safety and efficiency of the highway. Today, the highway network is 51.6 km long and includes seven tunnels (2.86 km) and 14 viaducts (5.11 km). Between Naples and Scafati (representing 50% of the network), the highway has two 15 m wide carriageways, three lanes in each direction, and an emergency lane along almost the entire stretch. Between Scafati and Salerno, there are two carriageways, each 9 m wide, with two lanes in each direction.

The highway network includes the following:

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Fourteen toll gates (Barriera Napoli Sud, Ponticelli, Portici–Ercolano, Torre del Greco, Torre Annunziata Nord, Torre Annunziata Sud, Pompei Ovest, Castellammare di Stabia, Pompei Est–Scafati, Diramazione SS 268, Angri Sud, Barriera Nocera Inferiore, Nocera Sud, Cava de’ Tirreni);

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Three service areas (Torre Annunziata Ovest, Alfaterna Ovest, Alfaterna Est);

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One hundred and one parking areas (one every 500 m on highways);

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Two service areas (Barriera Napoli Sud, Salerno).

The service areas on the highway network are distributed along the southbound carriageway at an average distance of 25 km and are open 24 h a day. In accordance with the agreement, the concessionaire Napoli–Pompei–Salerno has sub-concessioned the provision of fuel, catering, and other services to specialized operators under an access regime. In addition, the current concession provides for the construction of four service areas on public land.

The application of the framework has led to the development of the following WBS:

• Definition of the GIS model for the identification of areas suitable for the installation of RES, using the open source software QGIS v.3.28;
• Analysis of the results obtained and selection of design solutions;
• Definition of design proposals;
• Dimensioning of the project layout.

4. Results

As part of the territorial analysis activities aimed at defining project hypotheses, it was necessary to acquire and process accurate topographic data. To this end, a structured methodological approach was developed that allowed the processing and use of geographical information essential for understanding the morphology of the area under study. For the processing required for the design hypotheses, a systematic procedure was adopted to extract the essential topographical data. This activity was carried out using the Digital Terrain Model (DTM) for the highway section under study, including parts of the adjacent territory relevant to the overall assessment of the area. In the first phase, the DTM was imported into a GIS environment (QGIS) in the form of a georeferenced raster image in Geo TIFF format. This type of data, structured in matrix form, allows the terrain to be modeled in three dimensions and morphometric analyses to be carried out, which are essential for assessing the physical characteristics of the area. From the DTM, it was possible to obtain various exports useful for orographic analysis and subsequent energy simulations:

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Contour lines: generated at 25 m intervals to facilitate readability whilst maintaining an appropriate level of detail;

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Slope raster: used to assess ground slope;

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Aspect raster: useful for identifying the orientation of surfaces in relation to the sun;

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Hillshade raster: used to improve morphological visualization;

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Solar radiation raster: used to assess solar energy potential.

During the import process, the spatial reference system WGS 84/UTM zone 33 N (EPSG:32633) was assigned to the project, in accordance with the geographical location of the analyzed section. The contour lines were further processed by creating a 3D vector to facilitate the subsequent modeling and visualization phases. This three-dimensional representation supports the volumetric and spatial analysis of the orography, which is useful for assessing the suitability of the site for the installation of facilities or infrastructure. To optimize the readability of the DTM and its thematic features, a shading grid was generated within the QGIS environment. Among the products that can be derived from the DTM, the raster of slope exposure to true south (aspect) represents the orientation of topographic surfaces to true south (Figure 4). This parameter is particularly relevant for energy assessments as it directly affects the solar radiation received by the surfaces. The operation was performed in the QGIS environment using the “Raster > Analysis > Exposure” command available in the toolbar. The previously imported and georeferenced DTM raster was used as the input layer for the processing. The following options were selected when setting the processing parameters:

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Return 0 instead of −9999 for flat values to avoid the presence of zero values in pixels with zero slope, thus ensuring data continuity;

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Calculate margins to include boundary cells in the calculation and obtain a complete representation of the dataset.

Figure 4. A 3D map of the raster aspect.

Figure 4. A 3D map of the raster aspect.

The result of the processing is a grid representing the exposure of the slopes. Areas exposed to the south are shown in lighter colors, while those exposed to the north are shown in darker colors.

It should be noted that the calculation is so accurate that it also calculates the exposure in flat areas. However, as these areas are not usable in practice, the analysis of flat areas is not taken into account.

Slope raster

The slope map represents the steepness of the terrain expressed as a percentage. To generate this raster, use the geomorphological analysis processing tool, accessible via the Raster > Analysis > Slope path. In the QGIS tool dialogue box, select the Slope option, set the DTM as input, and give the output raster file a name. Also, select the option to express the slope in percent rather than degrees. The resulting raster allows you to analyze the slope of the terrain with percentage values ranging from 0 to 81%. From a cartographic point of view, the symbology used associate dark shades, tending towards black, with the lowest slopes (close to 0%), while progressively lighter shades, up to white, represent increasing slope values, up to the maximum recorded (81%). A slope of 100% corresponds to an angle of 45°. The relationship between slope (in percent) and angle (in degrees) is:

θ = arctan (slope/100)

(1)

The slope parameter plays a fundamental role in the analysis of slope stability: an increase in slope is generally associated with an increase in soil instability, which has a direct impact on the erosivity of surface water. In addition, slope affects the energy balance of the soil, as the amount of incident solar energy varies with the slope of the terrain.

Irradiation Raster

Additional information that can be derived from a DTM is a map of solar radiation at ground level, which is useful for quantifying incident solar energy expressed in Wh/m² on a daily basis. To generate this raster, it is necessary to first obtain aspect and slope maps as described above. Once these two rasters are available, you can use the QGIS processing environment, using the GRASS GIS module via the r.sun tool.

The GIS data were obtained from the “National Summary Database” (DataBase di Sintesi Nazionale—DBSN), an accessible national dataset provided by the Italian Army. Its high resolution and national coverage make the DBSN suitable for geospatial modeling and solar radiation analysis [35].

Using this tool will open a dialogue box where you will need to specify the elevation raster, the aspect raster, and the slope raster. It is also possible to set a minimum slope value to be taken into account in the calculation and to select a specific date of the year for which the solar radiation is to be calculated. Once the parameters have been set in the dialogue box, it is possible to proceed with the processing, which will return the grid of solar radiation on the ground (irradiance) for the specified day of the year.

It should be noted that the r.sun processing of the GRASS module in QGis returns as output the grid with values expressed in Wh/m² for a single day of the year (previously selected).

In order to achieve the objectives set, it was necessary to calculate the estimated average annual value of solar radiation incident on the ground, expressed in kWh/m². As QGIS does not provide an automatic method for this calculation, it was performed manually using a specific formula entered into the “Raster Calculator” according to the procedure described below:

• Calculation of daily solar radiation for four dates representative of the astronomical seasons:

  -

  15 January for winter (day 15 of 365);

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  15 April for spring (day 105 of 365);

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  15 July for summer (day 196 of 365);

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  15 October for autumn (day 288 of 365).

• Determination of the seasonal average daily value obtained as the arithmetic mean of the four calculated rasters (2):

(winter value + spring value + summer value + autumn value)/4

(2)

3.

Calculation of the annual average value obtained by multiplying the daily average value by the number of days in the year (3):

average daily value × 365

(3)

4.

Convert the unit of measurement from Wh/m² to kWh/m² and divide the result by 1000 (4):

(annual average)/1000

(4)

The resulting raster therefore represents the average annual solar radiation falling on each square meter of surface area, expressed in kWh/m².

Once the expression has been entered into the Raster Calculator and the save path has been defined, the raster containing the average annual insolation values is generated.

Below are pictures of the GIS model showing the 2D and 3D representation of the orography of the study area, highlighting the main geomorphological features of the area crossed by the highway route (Figure 5 and Figure 6).

From the cartographic analysis of the resulting raster, it can be observed that

-

Areas with light shades tending towards yellow correspond to lower radiation values, generally associated with north-facing slopes, as also highlighted in the three-dimensional extract;

-

Areas with darker colors tending towards red indicate high radiation values, usually referring to south-facing slopes and flat surfaces.

The radiation values are distributed along a scale ranging from 370 kWh/m² to 2658 kWh/m².

Analysis of Results Obtained and Proposed Design Solutions

The purpose of the analysis is to formulate design solutions that include the implementation of renewable energy generation systems to be built in the areas surrounding the A3 highway. Therefore, after analyzing the area affected by the existing highway route by studying the geomorphological characteristics contained in the DTM, the essential territorial data useful for this purpose were extracted. In this specific case, by studying the average annual data of solar radiation on the ground, it was decided to study the areas along the highway carriageway where sections of PV noise barriers could be installed. Once the areas with favorable characteristics, both in terms of solar radiation and solar exposure, were identified, a visual analysis of the state of the sites was carried out using Google Earth, which showed that along some sections of the highway there were areas of scattered settlements or buildings close to the road infrastructure, as well as a lack of specific noise mitigation measures, such as noise barriers on the sides of the carriageway. Therefore, we moved from an analysis of solar radiation data generated using QGis software to an actual analysis of the condition of the sites, proposing areas suitable for a design solution capable of achieving a dual purpose: ensuring adequate noise mitigation and contributing to the production of electricity from renewable sources. The proposed solution involves the installation of suitable PV sound-absorbing barriers on the identified sections of the highway.

On the other hand, as far as existing structures are concerned, the construction of suitable parking shelters with PV roofs could be considered. These shelters will be installed at existing service areas and at a panoramic rest area along the highway. In addition, PV systems will be installed on the roofs of existing buildings in service areas and some toll stations.

The selected project proposals cover the following areas:

-

Service areas:

○

Torre Annunziata West;

○

Alfaterna West;

○

Alfaterna Est.

-

Panoramic parking area, Golfo di Salerno.

-

Toll gates:

○

Napoli South;

○

Torre del Greco;

○

Torre Annunziata Nord;

○

Torre Annunziata Sud;

○

Castellammare di Stabia;

○

Angri Sud;

○

Nocera Inferiore.

-

Highway sections:

○

Section in the Pompei area (between Pompei Est and Castellammare di Stabia, from km 30 + 000 to km 30 + 560 in the direction of Salerno);

○

The section in the Angri area (between Angri Sud and Angri Nord, from km 25 + 000 to km 25 + 585 in the direction of Salerno);

○

Pagani section (between Nocera Inferiore and Angri Sud, from km 20 + 000 to km 20 + 585 in the direction of Salerno);

○

the Nocera section (between Alfaterna Est and Nocera Inferiore, from km 16 + 000 to km 17 + 100 in the direction of Salerno).

For each identified area, the relative values of the average annual solar radiation on the ground were determined, as shown in the following example (

Table 4. Average annual insolation on the ground by project area.

Service Area of Torre Annunziata West
ID	Value [kWh/m2]
Building	2104.00
Photovoltaic roof	2104.00
Service area of Alfaterna West
ID	Value [kWh/m2]
Building	2047.68
Photovoltaic roof	2047.68
Service area of Alfaterna Est
ID	Value [kWh/m2]
Building	2048.65
Photovoltaic roof	2048.65
Panoramic parking area in the Gulf of Salerno
ID	Value [kWh/m2]
Building	-
Photovoltaic roof	2319.00
Toll gate of Napoli South buildings
ID	Value [kWh/m2]
Building	2187.42
Photovoltaic roof	2187.42
Toll gate of Torre del Greco buildings
ID	Value [kWh/m2]
Building	2138.45
Photovoltaic roof	-
Toll gate of Torre Annunziata North buildings
ID	Value [kWh/m2]
Building	2174.48
Photovoltaic roof	-
Toll gate of Torre Annunziata South buildings
ID	Value [kWh/m2]
Building	2174.48
Photovoltaic roof	-
Toll gate of Castellammare di Stabia buildings
ID	Value [kWh/m2]
Building	2104.94
Photovoltaic roof	-
Toll gate of Torre Angri South buildings
ID	Value [kWh/m2]
Building	2103.69
Photovoltaic roof	2014.38
Toll gate of Nocera Inferiore buildings
ID	Value [kWh/m2]
Building	2022.71
Photovoltaic roof	-

).

The project proposals that can be applied to the areas previously identified concern the production of electricity from renewable energy sources through the installation of PV systems. This proposal has been developed on the basis of an analysis of the existing infrastructure along the highway network, with the aim of redeveloping and reusing part of the available land. A preliminary feasibility study has been carried out in the three service areas identified, Torre Annunziata West, Alfaterna Est, and Alfaterna West, in order to identify the areas that are actually suitable for the installation of PV systems. In particular, it is planned to use the roofs of the highway service areas, the canopies of the petrol stations, and the open-air car parks by installing PV canopies. Below is a satellite image showing the highway route (in green) and the intervention areas along it. It was necessary to create a union frame in which each square represents the part of the territory affected by the study areas (Figure 7).

The design hypotheses envisaged in this study are located at different points along the highway sections, and the total area available for the project works is 27,100 m² (2.7 ha).

In order to assess the area’s potential for electricity generation from photovoltaic systems, we estimate its annual energy production using the following formula (5):

E = A × G × η

(5)

where

E is the annual electricity production [kWh/year];

A is the total surface area available for the installation of photovoltaic systems [m²];

G is the average annual solar radiation on the surface [kWh/m²/year];

η is the overall efficiency of the photovoltaic system (including module efficiency, inverter losses, orientation, and shading).

Based on an available area of A = 27,100 m², an average annual solar radiation of G = 2300 kWh/m²/year (an average of the measured values of 2000 and 2600), and a system efficiency of η = 0.15, the expected annual energy production is given by Equation (6).

E = 27,100 × 2300 × 0.15 = 9,364,500 kWh/year ≈ 9.36 GWh/year

(6)

This level of production is significant. It could meet the annual energy needs of around 3500 electric vehicles (assuming 10,000 km per vehicle per year and consumption of 27 kWh per 100 km) or around 3400 Italian households (assuming average consumption of 2700 kWh per household per year). While this value does not cover regional energy demand, it represents a substantial local contribution to decarbonization. This is particularly notable given that it is based entirely on existing infrastructure and avoids further land consumption.

Based on the estimated annual production, the environmental benefits of installing photovoltaic systems in the identified areas can also be quantified. Using an average emission factor of 0.42 tons of CO₂ avoided per MWh produced from renewable sources for the Italian electricity grid [36], this results in an annual reduction in emissions of (7).

9360 MWh/year × 0.42 tCO₂/MWh = 3931 tCO₂/year

(7)

It should be noted that calculations (6) and (7) are rough estimates based on average values, intended solely to provide an indication of the potential scale of impact. Nevertheless, the results clearly demonstrate the significant positive contribution that integrating photovoltaics into highway infrastructure could make to decarbonization, particularly if implemented nationwide.

Regarding the panoramic rest area overlooking the Gulf of Salerno, the project could include the use of spaces currently used for vehicle parking by covering them with PV shelters. Photovoltaic shelters are car park roofs that serve the dual purpose of providing shade for parked vehicles and generating renewable energy. The PV system for electricity generation is located on the sloping roof and can be connected to the grid or can independently power the charging stations for electric cars parked there. Of the 14 toll stations along the highway, 7 have been selected for the installation of PV modules on the roofs of the toll booths and adjacent technical buildings, where they exist, and for the construction of carports with PV roofs at the Napoli Sud and Angri Sud toll stations, which already have sufficient parking space. These specific stations have been selected on the basis of technical and functional optimization criteria, including the availability of adequate space for the installation of larger systems and the ease of setting up infrastructure for recharging electric vehicles in their vicinity, to promote the integration of distributed generation and sustainable mobility. Four points along the highway have been identified where the construction of PV noise barriers has been proposed due to the lack of appropriate noise mitigation systems.

5. Discussion

Looking back over the content and stages of development of the work, the multiple benefits of the proposed framework emerge clearly, both in terms of favorable energy prospects and from a managerial, environmental, methodological, and technological point of view, opening up the possibility for discussion in the following areas of interest:

-

Investment planning;

-

Design of works;

-

Investment efficiency;

-

Traffic management;

-

Mitigation and monitoring of environmental parameters;

-

Integration and development of innovative technologies.

By analyzing these areas, it can be seen how the analysis of international and national scenarios, based on regulatory objectives, clearly outlines the expected values and implementation times. These objectives require detailed analysis and operational plans for their implementation. It is therefore useful to address the identification of the energy needs of a significant type of asset, focusing on the energy transition and sustainable management of transport infrastructure, in parallel with the processes of monitoring the safety of works.

The proposed methodology may be relevant in the context of the electric and digital transition of the automotive sector, as it aims to minimize environmental impacts and the consumption of new land. The interventions are concentrated in areas relevant to the highway network, transforming it into a productive environment capable of regenerating the energy needed to sustain traffic flows and exporting it to the national electricity grid.

This autonomy of highway assets is not in contradiction with proposals to diversify energy supplies to create more efficient and sustainable mixes, reducing the complexity of the remaining part. The highway management regime, through the concessions that define the obligations of the concessionaires–operators, promotes the efficient planning and management of the works for the construction of the infrastructure necessary for the energy transition, the proper management of the life cycle of the facilities, and the implementation of ESG systems and/or environmental protocols such as ENVISION, including through appropriate tariff incentives on toll revenues, minimizing the possible negative impacts of decommissioning, the rules of which are not yet well defined [37].

Before analyzing the energy data resulting from the application of the framework to the A3 case study, it is worth highlighting some of the benefits of potential digital management of asset information in terms of the effectiveness, efficiency, and cost-effectiveness of public works. In particular, an economic framework for a general sustainability project for an entire section of highway of approximately 60 km, assuming uniform technologies and defined prices, can indicate the possibility of achieving standardized work costs as far as possible. This creates economic and environmental benefits, using computerized environments to define databases capable of improving the experience of public asset managers and the interaction of work with the construction environment, including interference management, and even designing analyses based on machine learning methods [38].

The transition to electric vehicles is a key element in decarbonizing the transport sector and achieving the European Union’s climate change targets. According to projections by the International Energy Agency (IEA), global sales of light electric vehicles could reach 40% by 2030 and almost 55% by 2035, based on current policies [39].

In Italy, the National Integrated Energy and Climate Plan (PNIEC) has set a target of 4.3 million electric vehicles on the road by 2030 [40]. However, by the end of 2023, the electric vehicle fleet in Italy will be only 220,000 units, representing 0.5% of the total car fleet and 5% of the target set. These figures highlight a significant discrepancy between the targets and the current situation, suggesting that more effective policies and incentives are needed to accelerate the uptake of electric vehicles. The penetration of electric vehicles will have a significant impact on the management of highway infrastructure. A significant increase in the number of BEVs will require the expansion and adaptation of charging infrastructure along highways, as well as efficient management of energy demand to avoid overloading the electricity grid. In addition, the integration of innovative technologies such as intelligent energy management systems and fast charging solutions will be key to supporting this transition and ensuring a satisfactory user experience.

Recent studies have explored various strategies for integrating photovoltaic systems into road infrastructure. Ebner et al. [41] introduced the PV-SÜD concept, which involves installing steel-framed photovoltaic structures above highway lanes in Germany and Austria. While this approach is technically feasible and modular, it involves high infrastructure costs and a certain degree of structural complexity. Peerlings et al. [42] studied the integration of vertical bifacial photovoltaic modules into noise barriers in the Netherlands. They estimated a national potential of 200 GWh/year, which would enable the charging of solar-powered electric vehicles near service stations, meeting over 80% of the forecast demand for 2030. Jiang et al. [43] proposed a comprehensive planning strategy for installing photovoltaic systems on Chinese highways, introducing the concepts of Road Solar Capacity (RSC) and Photovoltaic-Available Road Area (PRA). This approach incorporates detailed solar radiation modeling, GIS-based PRA estimation, and spatial matching with local energy consumption via the Road Energy Consumption Circle (RECC). Although robust, their method remains analytically complex and requires a large amount of data. The proposed research offers a simplified, scalable, GIS-based methodology for assessing photovoltaic potential along a real highway section in Italy. This approach prioritizes available surfaces within the transport corridor (e.g., rest areas and noise barriers), enabling a rapid assessment of installable photovoltaic capacity without the need for extensive infrastructure or spatial modeling. This balance between feasibility, replicability, and sustainability means the method can be replicated in Mediterranean regions characterized by high solar availability and spatial constraints.

In summary, while research provides tools to improve energy efficiency and sustainability of highway infrastructure, the success of the transition to electric mobility will also depend on the ability to address the challenges associated with the uptake of electric vehicles through appropriate policies, investment in infrastructure, and technological innovation.

6. Conclusions

The growing awareness of the need to reduce greenhouse gas emissions and promote more sustainable mobility has led governments, institutions, and road infrastructure operators to adopt increasingly integrated, digital, and energy-efficient strategies. In this context, this study has taken a systematic and multidisciplinary approach to the issue of energy transition in the highway sector, proposing a digital framework applicable to such infrastructure to support electric mobility through the local production of energy from renewable sources. Through the analysis of a representative case study, the A3 Naples–Pompei–Salerno highway section, it has been possible to demonstrate the feasibility of possible solutions for the integration of photovoltaic systems in highway areas. The simulations carried out, based on GIS processing and morphometric analysis of the terrain, highlighted the photovoltaic potential that could be installed over an area of 27,100 m². This result, in line with the decarbonization projections developed by IRENA and in line with the objectives of the PNIEC, is of strategic value in terms of a self-sufficient, smart, and resilient road network.

The proposed approach has improved interoperable digital tools in a GIS environment to support decisions in the planning, design, and management phases of interventions. The use of these tools has made it possible to generate a robust model capable of providing spatial and technical information essential for assessing energy potential and defining localized intervention strategies.

The design solutions potentially identified, such as photovoltaic noise barriers, electric vehicle shelters, and installations on existing buildings, demonstrate the possibility of redeveloping already built spaces and, more importantly, of transforming infrastructure from a passive element to an active node in the national energy system, without increasing land consumption.

The research also highlighted the need for systemic change, not limited to technological aspects, but including regulations, standards, incentives, and centralized governance through a national transport sustainability authority. This body, acting in synergy with public authorities and private operators, could coordinate investments, monitor environmental results, and provide incentives for virtuous practices through economic and regulatory instruments.

In conclusion, the framework developed is proposed as an operational model that can be replicated at the national level, capable of combining digitization, sustainability, and innovation. If properly supported by coherent public policies, it could be a strategic tool for the decarbonization of the transport sector, contributing to the achievement of European climate goals and to the creation of a more efficient, resilient, and sustainable infrastructure system.

Future developments

The results of the trial on the A3 Naples–Pompei–Salerno highway confirm the validity of the proposed approach, demonstrating that it is technically possible to cover a significant part of the energy requirements of electric mobility through photovoltaic systems installed in highway areas. These data open up promising scenarios for the integration of road infrastructure and the national electricity system, supporting the creation of a network of smart roads powered by renewable sources, capable not only of managing part of their own energy needs autonomously but also of contributing to the overall resilience of the energy network through energy exchange, storage, and intelligent management systems. In this context, the case study highlighted the opportunity to develop an integrated and centralized digital system capable of collecting, processing, and synergistically using data from infrastructure assets to support operational and strategic decisions. For future developments, integration with BIM systems for territorial modeling, demand simulation, and cost–benefit analysis is desirable, as well as the adoption of technologies such as Digital Twin, Internet of Things (IoT), and Artificial Intelligence (AI), which could facilitate the predictive management of energy and vehicle flows, promoting the convergence between Smart Roads and Smart Grids [44]. Furthermore, the photovoltaic potential can be modeled in detail by integrating different technologies (e.g., monocrystalline, thin film, or bifacial) and installation types, including fixed or solar tracking structures, in order to estimate actual energy production more accurately. All this would allow dynamic, continuous, and predictive control of energy flows in favor of the energy balance paradigm between production, storage, consumption, and vehicle traffic, and would be another concrete response to the challenges related to the variability of renewable energy production and the management of BEV penetration. From a methodological and regulatory point of view, it is necessary to adopt common ontologies and standards to ensure interoperability between digital environments, to promote a regulatory framework in line with the principles of the DNSH and the European Green Deal, and to establish a national control room supported by a Transport Sustainability Authority capable of coordinating public and private stakeholders.