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Article

Factors Influencing the Carbon Footprint of Major Road Infrastructure—A Case Study of the Učka Tunnel

by
Hrvoje Grofelnik
* and
Nataša Kovačić
Faculty of Tourism and Hospitality Management, University of Rijeka, 51410 Opatija, Croatia
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(5), 4461; https://doi.org/10.3390/su15054461
Submission received: 31 January 2023 / Revised: 27 February 2023 / Accepted: 28 February 2023 / Published: 2 March 2023
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Abstract

:
In addition to its positive socioeconomic impact, tourism also has some negative effects on the environment, particularly through carbon dioxide (CO2) emissions. Although the impact of tourism on the environment is visible, many of the cause–effect relationships have not yet been adequately explored. In order to determine individual factors regarding the temporal variation in the carbon footprint of a major road infrastructure facility (the Učka Tunnel, Croatia), a regression analysis was conducted. The study analyzes the carbon footprint of the pre-pandemic and pandemic periods and uses factors at the national and regional levels influencing the region of Istria County, as representative of the developed tourism regions in the Mediterranean. The results of the research provide theoretical insight into the sustainability and cause–effect relationships between the economic and social factors of road transport in tourism-developed destinations, with characteristic seasonality. At the application level, the research results can be used to predict the temporal variations in the environmental impacts of road infrastructure, as well as economic parameters that can be used in the prediction process and crisis management models of major road facilities.

1. Introduction

The impact of human activities on environmental change has increasingly become the focus of modern scientific research. In the context of climate change mitigation, greenhouse gas (GHG) emissions and carbon dioxide (CO2), in particular, stand out. One of the largest shares of the economy’s overall impact on the environment in terms of CO2 emissions comes from passenger and freight transport, to which tourism also contributes significantly [1]. In contemporary research on the relationship between the anthropogenic impact of CO2 emissions into the atmosphere, and the natural environment as an element that absorbs CO2 from the atmosphere, the carbon footprint method is increasingly utilized. Current research on the impact of human activities on the environment and development strategies both aim to reduce the overall carbon footprint [2].
This paper specifically examines the environmental impact of CO2 emissions in Istria County (Croatia), an area that is economically focused on tourism. Tourism in this region is predominantly based on road transport, as shown by the figures in this research and confirmed by the data on the incoming traffic at the border crossings of Kaštel and Plovanija [3], which inevitably affect the environment in regards to CO2 emissions. The carbon footprint can be measured at the global level in terms of the average biocapacity of the global ecosystem, while at the local level, it is perceived in the context of the absorption biocapacity of a particular isolated area [4]. Most research on the carbon footprint of tourism in the relevant scientific databases addresses the impact of carbon emissions at the global or national level [5,6]. In addition, most carbon footprint studies do not analyze the factors that influence changes in the intensity and seasonality of emissions, but rather view them on an annual basis, without considering seasonality and monthly variations [7]. To address this gap in the existing research, the focus of this paper is on a case study of one of the large and strategically important road infrastructure facilities and the measurement of factors that influence its monthly and seasonal variations in the environmental impact of CO2 emissions. A special place in this research is also given to the separation of the individual factors that influence the intensity and temporal variations of the CO2 footprint at the national and regional level.
The aim of this research is to contribute to the clarification of the cause–effect relationships between economic and social factors that influence the seasonality of the transport-related carbon footprint in predominantly tourist areas. At the applied level, the research results can be used for projections of future environmental impacts, as well as for projections of economic parameters that influence the normal and crisis management of major road infrastructure facilities. The study focuses on the analysis of the case study of the Učka Tunnel, which strategically connects the two of the most developed tourist regions of the Republic of Croatia [8], as well as the region of Istria with the rest of the national territory. The Učka Tunnel is also an important road connection of Central Europe with Istria, the important tourist destination of the north Mediterranean region. As a highly touristic region, Istria exhibits the typical characteristics of a Mediterranean summer tourist destination and depends primarily on the arrival of international tourists by means of private road transportation [8,9,10,11].
The goal of this research is to distinguish individual factors that influence the intensity and seasonality of the carbon footprint of the infrastructure of major roads.
To achieve the stated goal, six specific factors were singled out, and the following hypotheses were formed.
  • H-1: There is a positive correlation between tourist arrivals in the studied region and the increase in the carbon footprint of the traffic in the Učka Tunnel.
  • H-2: There is a positive correlation between overnight stays of tourists in the studied region and the increase in the carbon footprint of the traffic in the Učka Tunnel.
  • H-3: There is a positive correlation between the economic activity in the studied region and the increase in the carbon footprint of the traffic in the Učka Tunnel.
  • H-4: There is a positive correlation between the level of employment in the studied region and the increase in the carbon footprint of the traffic in the Učka Tunnel.
  • H-5: There is a negative correlation between the level of unemployment in the studied region and the increase in the carbon footprint of the traffic in the Učka Tunnel.
  • H-6: There is a negative correlation between the COVID-19 pandemic in the studied region and the increase in the carbon footprint of the traffic in the Učka Tunnel.

2. Theoretical Background

The economic development at the national level depends largely on the transport system and all of its possible uses. Since important international transport routes pass through Croatia, the transport system must fulfil a double task—the international and national transportation of a considerable number of people (including tourists), as well as a significant flows of goods. The long-standing condition for the continuous development at the national level, which implies the quality of transport and transport infrastructure, i.e., the identification of the technical-technological and organizational deficiencies of the national transport system in relation to the environment, is the priority for development and a sustainable future [12]. Efficient transportation infrastructure reduces travel time and provides better connections between destinations [13,14], with a positive impact [15] when transportation issues are not poorly managed [16], i.e., when risks to the environment and communities are minimized. Mitigating regional isolation through tunnel connections and improved road infrastructure in general helps address geographic isolation and population decline [17], mainly due to the positive relationship between regional economic development and road infrastructure [18,19]. The potential of road transport infrastructure for the development of tourist destinations is also reflected in employment opportunities for local people [20], but unlike other local actors, it is often underestimated by authorities [21]. In its 40 years of existence, the Učka Tunnel has achieved the above-described economic and strategic goals, which can also be seen in regards to its current upgrading and modernization.
It is a great challenge to operationalize sustainability in major infrastructural (tunnelling) projects [22] and integrate all aspects of sustainability in managing them over the tunnel’s long life span. Environmental impacts from road tunnels attracted significant scientific attention in the late 1990s and early 2000s [23,24,25,26,27], but the carbon footprint methodology had not been developed at that time. The construction of transportation infrastructure is often viewed through the lens of engineering factors, while the parameters related to GHG emissions, the focus of this work, are often neglected or deemed as secondary. The quantified emissions of tunnel infrastructure, i.e., the environmental impact of road transport, allow for the monitoring of their changes over the time and exist in relation to economic and technological development [28]. Differences in tunnels, as well as differences in research approaches among various studies determining GHG emissions per one meter of a tunnel [29,30], indicate the need to consider the entire lifecycle of a tunnel to assess its GHG footprint [31].
Several previous studies on GHG emissions, using road tunnels as an example, are based on the life cycle assessment method (LCA) [29,30,32,33], as it is a tool for assessing the environmental impact (emissions) of transportation infrastructure. Contrary to the perception of high life-cycle emissions during operation [34,35], emissions during road tunnel construction are also proven significant or even greater than those during the operational phase [30,32,36]. The measurement of GHG emissions is part of a suitable approach to determine the sustainability of tunnels during construction, i.e., a more holistic approach to environmental impact assessment (EIA) [37], while sometimes, emissions from existing tunnels are determined to predict emissions in new tunnel construction [38]. Road gradients, vehicle speeds, and days of the week (in relation to different fleet compositions) are also recognized as significant emission factors [28]. However, technological innovation also provides the opportunity to capture and use a great share of CO2 emissions for human benefit [39].
Whether in regards to tunnel construction, fire hazards, ventilation, safety, traffic risks or accidents, or various simulation or prediction methods, the relevant scientific databases show that the technical focus predominates in the recent research on road tunnel infrastructure, as noted in the work of [40,41,42,43,44,45,46,47]. In the existing studies, the socio-economic perspective is missing, as well as the impact of large infrastructure objects, such as the one studied in this paper (the Učka road tunnel), and studies prevailingly analyze the impacts of infrastructure on international trade [48,49,50,51], while regional development is rather neglected. The construction of road tunnels, such as the Učka Tunnel, has important strategic, economic, political and social value for the integral national transport system [52]. In light of the strategic development potential of road infrastructure and the fact that the key role of transport systems is to provide a network for the movement of people and goods [15], destination development policies need to be more holistic and take into account the indirect effects and impacts of transport infrastructure on a destination [21], including the perspective of local stakeholders affected by the infrastructure [53].
There are only few studies that analyze the relationships and impacts of road tunnel infrastructure and regional tourism. It is interesting to note that the social significance of the existence of this type of infrastructure is mainly studied in more isolated areas or areas that are otherwise challenged due to their specificities—for example, in the mountainous regions of the Alps [54] or on remote islands such as in Iceland [17] or the Faroe Islands [21].
Road transport, which at 77% in 2020, accounts for the largest share of total EU transport-related GHG emissions, is expected to be decarbonized in the coming decades through measures such as the promotion of low-carbon fuels, electric cars, or a shift to public transport [55]. The transformation of the transport system is not a short process, and it will take a long period of time to achieve carbon neutral goals. The fact is that international tourists arriving in the Republic of Croatia predominantly travel by private car [56,57], as is shown by the region-related data obtained for this research. It is therefore logical to expect that the carbon footprint of road traffic will continue to influence the environment for a considerable number of years. In this light, this research contributes to the analysis of the current state, but also to the future improvements in road infrastructure management.

3. Materials and Methods

For the purpose of this research, the authors collected statistical data at the national, regional, and local levels in direct contact with the relevant institutions. The timeline data series in the research is analysed monthly, starting in January 2015 and finishing in December 2020. The following institutions and companies were contacted to gather the relevant datasets: BINA-Istra, a joint stock company for the financing, construction, management, and maintenance of motorways (concessionaire of the Učka Tunnel and the Istrian Ipsilon Highway), the Croatian Bureau of Statistics, the Croatian Employment Service (national and regional), the Croatian Pension Insurance Institute (Office for Strategic Analysis, Development, and Project Management), the Teaching Institute for Public Health of Istria County.
In defining the economic activity of the observed area, it was not possible to obtain regional indicators, so indicators at the national level were considered in the form of the Coincident Economic Index (CEIZ). The CEIZ (Figure 1) is a composite economic indicator developed by the Institute of Economics in Zagreb, by the parallel application of a dynamic factor model and a Markov switching model [58]. It provides information on national business cycle conditions. Therefore, the CEIZ index value changes monthly, indicating the current state of the national economy.
The data from the Croatian Pension Insurance Institute on the number of “insured persons” (employed by legal entities and natural persons, as well as by tradesmen, farmers, and in independent professional activities) were used to determine the number of employed persons. It was not possible to obtain the data for the monthly dynamics from the Croatian Bureau of Statistics (the usual source of the number of employed persons) required for this study. The data from the Pension Insurance Institute [59], available for each individual region (down to the local level), are collected on the last day of the month, according to the place of work and not the place of business (Figure 2). The above data are provided to the authors in the form of interactive datasets.
The impact of the number of unemployed persons is quantified using online statistics from the Croatian Employment Service [60], which allows for the monthly retrieval of data for the observed period (Figure 2). Registered unemployed persons are persons between 15 and 65 years of age who are able to work or partially able to work, who are not employed, are actively seeking and available for work, and who meet the criteria of the provisions of the Labor Market Act (OG No. 119/18).
The number of overnight stays and tourist arrivals are among the basic indicators of tourism development in the Republic of Croatia, monitored at all levels (local, regional, and national) and consolidated in the databases of the regional authorities for destination management, the Croatian Bureau of Statistics, and the Ministry of Tourism (Figure 3). For this paper, data from the online report “Tourist Arrivals and Overnights in Istria” for the observed period (2015–2020) were used [61].
Data on road traffic through the Učka Tunnel were obtained by direct contact with the concessionaire of the Učka Tunnel and the Istrian Ipsilon Highway and were converted into specific CO2 emission values (kg) using the carbon footprint method, according to the following carbon footprint equation:
CF Učka = ∑ (distance* × emission coefficients**)
* Road distance—Učka Tunnel (km).
** Different coefficients are used for calculating the carbon footprint of different vehicles.
The carbon footprint of daily road traffic in the Učka Tunnel was calculated based on vehicle kilometres on the observed road section and CO2 emission coefficients by vehicle category, i.e., fuel consumption of each vehicle group [4,62,63,64]. The concessionaire BINA-Istra monitors tunnel passage statistics for the following five categories of vehicles:
  • Category I: motor vehicles with two axles and a height of up to 1.90 m;
  • Category IA: motorcycles, motorized tricycles and quadricycles;
  • Category II: (a) motor vehicles with two axles and a height of more than 1.90 m, whose maximum permissible mass does not exceed 3500 kg; and (b) motor vehicles with two axles and a height of less than 1.90 m, towing a trailer, regardless of the number of axles and the height of the trailer;
  • Category III: (a) motor vehicles with two or three axles and a maximum permissible mass exceeding 3500 kg; (b) motor vehicles with two axles and a maximum permissible mass exceeding 3500 kg, towing a single-axle trailer; and (c) motor vehicles in category IIa, towing a trailer, regardless of the number of axles of the trailer;
  • Category IV: (a) motor vehicles with four or more axles and a maximum permissible mass exceeding 3500 kg; (b) motor vehicles with two axles and a maximum permissible mass exceeding 3500 kg towing a trailer with two or more axles; and (c) motor vehicles with three axles and a maximum permissible mass exceeding 3500 kg, towing a trailer, regardless of the number of axles on the trailer [65].
The obtained values of the carbon footprint on a monthly basis for the period from 2015 to 2020 are linked to individual factors/variables in regression models in order to obtain the most reliable combination of factors/variables for use in future environmental impact and infrastructure management projections.
The following independent variables were used in multiple regression (absolute, numeric):
  • (β1darr) domestic tourist arrivals—number of tourists (in thousands) in Istria County;
  • (β2farr) foreign tourist arrivals—number of tourists (in thousands) in Istria County;
  • (β3dov) domestic tourist overnight—number of tourists (in thousands) in Istria County;
  • (β4fov) foreign tourist overnight—number of tourists (in thousands) in Istria County;
  • (β5em) employed—number of employed persons (in thousands) in Istria County;
  • (β6unem) unemployed—number of unemployed persons (in thousands) in Istria County;
  • (β7ceiz) CEIZ index—monthly composite business cycle indicator (Republic of Croatia);
  • (β8covid) COVID-19—monthly number of COVID-19 cases in Istria County;
  • Model 0—All 2015–2020
lnCF = β0 + β1darr + β2farr + β3dov + β4fov + β5em + β6unem + β7ceiz + β8covid
Model 0 (all variables) was rejected after checking test for heteroscedasticity and residual independence. The variables showed high autocorrelation. In model 0, variables β3dov, β4fov, and β5em showed a high level of autocorrelation with the monthly oscillation of the carbon footprint in the Učka Tunnel due to the dominant role of tourism seasonality connected with the increase in road traffic in the summer tourist season. The seasonality of tourism determines major oscillation in the region’s overall economic activity, which is not only visible in the number of overnight stays of domestic and foreign tourists, but also in the seasonal rise in the general number of employed persons in the Istria region. It is important to note that the labor force in the tourist season comes not only from the local labor market, but also from outside of the Istria region.
After an analysis of the effects on the regression models and their results, the number of variables was reduced to four independent variables.
lnCF = β0 + β1darr + β2farr + β6unem + β7ceiz
The modified model with a reduced number of variables met all conditions for running a linear regression.
The standard errors of heteroscedasticity in the regression were confirmed by Breusch–Pagan and Abried–Whites tests. To test whether the residuals from a regression analysis are independent, the Durbin–Watson (DW) test was used. The DW values for model 0 are 1.58 for model 1 and model 2, indicating that there is no significant autocorrelation. The Pearson correlation coefficient and variance inflation factors (VIP) were used to detect multicollinearity. The values of the Pearson correlation coefficients ranged from 0.10 to 0.18 (indicating that collinearity among the variables is not likely to exist), and the values of the VIPs ranged from 1.05 to 2.41 (also indicating low correlation among the variables used).
The basic model for multiple linear regression is set as follows:
  • Model 1—2015–2020
lnCF = β0 + β1darr + β2farr + β6unem + β7ceiz
Model 1 was created for the entire period under study, from 2015 to 2020.
  • Model 2—2015–2019
lnCF = β0 + β1darr + β2farr + β6unem + β7ceiz
Model 2 was constructed for the period from 2015 to 2019, excluding the year with the outbreak of the COVID-19 pandemic, which had a significant impact on all social parameters, including those observed as independent variables in this study.

4. Results

The results of the carbon footprint in the Učka Tunnel show that the monthly value of the emission levels are highly seasonal and are influenced by tourism activity. The peak of the summer tourism season in July and August leads to an increase in the number of vehicles passing through the Učka Tunnel (Figure 4). The total CF of the Učka Tunnel in the period from 2015 to 2020 was 17,323,540 kg of CO2, with an average of 2,887,257 kg of CO2 per year.
In analyzing the influence of each variable on the CF of the Učka Tunnel, two regression models were created (Table 1), each containing four variables that were found to be reliable. The models differ in time, indicating the importance of each variable in relation to common years and a period that includes a year with significant impact from the COVID-19 pandemic on society as a whole, including tourism and related CO2 emissions.

4.1. Model 1 (2015–2020)

Interpretation of Model 1:
  • For 1000 additional domestic guest tourist arrivals, the traffic volume in the Učka Tunnel increases by 0.808%. This means that for an increase of 1000 arrivals of domestic guests, the carbon footprint increases by 23,329 kg of CO2 on an annual basis.
  • For 1000 additional foreign guest tourist arrivals, the traffic volume in the Učka Tunnel increases by 0.042%. This means that for an increase of 1000 arrivals of foreign guests, the carbon footprint increases by 1213 kg CO2 on an annual basis.
  • If unemployment increases by 1000 people, traffic in the Učka Tunnel decreases by 4.818%. This means that for an increase in the number of unemployed by 1000 people, the carbon footprint decreases by 139,108 kg CO2 on an annual basis.
  • For a one percentage point increase in the CEIZ index at the national level, traffic in the Učka Tunnel increases by 3.146%. This means that for a one percentage point increase in the CEIZ index, the annual level increases the carbon footprint by 90,833 kg CO2.

4.2. Model 2 (2015–2019)

Interpretation of Model 2:
  • For 1000 additional domestic guest tourist arrivals, the traffic volume in the Učka Tunnel increases by 0.423%. This means that for an increase of 1000 arrivals of domestic guests on an annual basis, the carbon footprint increases by 12,213 kg of CO2.
  • For 1000 additional foreign guest tourist arrivals, the traffic volume in the Učka Tunnel increases by 0.045%. This means that for an increase of 1000 arrivals of foreign guests annually, the carbon footprint increases by 1299 kg CO2.
  • If unemployment increases by 1000 people, traffic in the Učka Tunnel decreases by 5.752%. This means that for a 1000 person increase in unemployment annually, the carbon footprint is reduced by 166,075 kg CO2.
  • The changes in the CEIZ index for the observed period were not statistically significant for interpretation.

5. Discussion

Istria is the most developed coastal tourist region in Croatia and shares tourist characteristics with the rest of the larger Mediterranean tourist region. By land, Istria is the closest seaside destination to the Central European tourist markets. Its tourism is characterized by seasonality (Figure 3) and depends mainly on road transport [57]. The research found a clear positive correlation between regional tourism in the Istrian region and its impact on the increase in traffic intensity, consequently showing greater negative impact on the environment, as illustrated using the example of the Učka Tunnel (Models 1 and 2).
The results of the conducted research confirm the emphasised seasonality of tourism in Istria, with a summer maximum of tourist arrivals and overnight stays. Although when testing the preconditions and reliability of the input data in the regression models, the data on overnight stays of tourists (H-2) could not be reliably used, the use of data regarding the arrivals of domestic and foreign tourists confirmed the hypothesis (H-1). Therefore, the research confirms that the increase in arrivals of domestic and foreign tourists also increases the traffic intensity in the Učka Tunnel, i.e., increases its carbon footprint.
The research confirmed the positive influence of economic activity at the national level (using the CEIZ index; Figure 1) on the increase in traffic intensity in the Učka Tunnel. The established positive relationship is visible for the observation period from 2015 to 2020 (H-3). At the same time, it is important to stress that the level of statistical reliability of these data is insufficient for both periods, i.e., for comparison with the period from 2015 to 2019 (Table 1). The above indicates that under the conditions of large and sudden economic changes at the national level (Model 1), the CEIZ index can be a good support for the projection of traffic intensity in the Učka Tunnel, while under the conditions of normal fluctuations, it does not prove to be statistically significant (Model 1). These data are valuable as a possible input for models of transport infrastructure management from the environmental, safety, and security perspective in relation to crisis management.
Indicators of monthly trends in the number of employed persons (Figure 2) at the regional level (Istria) (H-4) were predicted as one of the economic variables covering all economic activities (including tourism). However, the data were not used in the regression model because they did not meet the conditions of heteroscedasticity and residual independence, and the variables had high autocorrelation. The monthly data on the number of employed persons has not been used because its autocorrelation with the seasonality of tourist activities is too high. In contrast to the trend in the number of employed, a negative correlation between the variables was confirmed for the monthly changes in the number of unemployed persons (H-5), and it was found that the increase in the number of unemployed negatively affects the traffic intensity in the Učka Tunnel, i.e., reduces the carbon footprint.
In addition to the five years studied (2015–2019), the period studied in Model 1 included 2020, marked by the occurrence of the COVID-19 pandemic, requiring special attention when interpreting the data. The impact of the registered number of COVID-infected people in Istria County (H-6) on the traffic in the Učka Tunnel was not directly confirmed. When interpreting this data, it is necessary to take into account the very small number of COVID-infected people [66], which leads to the fact that the conditions of this variable for the interpretation of the regression models (heteroscedasticity, residual independence, and high autocorrelation of the variables) are not met. It should also be noted that hypothesis H-6, relating the impact of the pandemic on traffic in the Učka Tunnel, was confirmed by the impact of the pandemic on the decrease in tourist arrivals, which in turn, was reflected in a significant decrease in traffic through the Učka Tunnel after the pandemic outbreak in March 2020. The consequences of the anti-epidemic measures in spring of 2020, which limited the spatial mobility of people, are evident in the research results, reflecting the decreased intensity of national and regional road traffic, as well as tourist arrivals, in the summer season 2020 [67].
A comparison of models 1 and 2 shows the increasing importance of domestic tourism for Model 1, which includes the year 2020. It shows that the pandemic affects not only the absolute carbon footprint, but also the structure of tourist arrivals (as observed during the 2020 pandemic season, when the share of domestic tourists increased).
It is important to note that in Model 1 and Model 2, notwithstanding the fact that the models show a relatively larger impact of domestic tourist arrivals on carbon footprint growth, the overall absolute impact of foreign tourist arrivals on the environment is larger, as the average annual number of arrivals is 14.7 times higher (in the period of 2015–2020) than the number of domestic arrivals [3,11,57]. The difference between the influence of the variables of domestic and foreign tourist arrivals to Istria through the Učka Tunnel in the regression models is a consequence of the tunnel’s geographic position. Its role in the national traffic system, which predominantly connects the region with the rest of the national territory, is reflected in the increased influence of domestic guests on the carbon footprint of the tunnel, while a significant portion of foreign visitors arrive in Istria from other traffic directions, i.e., from Slovenia and Italy, which do not use the Učka Tunnel.
Comparing the effects of unemployment in Istria County on the carbon footprint of the Učka Tunnel in models 1 and 2, it is notable that unemployment, as a variable for predicting the traffic intensity and carbon footprint of the Učka Tunnel, proved to be the most stable and statistically significant under normal circumstances (Table 1).

6. Conclusions

Croatia is a tourist destination with a distinct summer season, and one of its main characteristics is that a large proportion of guests arrive by road, mainly from Central Europe. Notwithstanding the focus of modern technological advances and development strategies on sustainable and carbon-neutral road transport, the spatial circulation of people (including tourists) is still responsible for significant environmental impacts. The conducted study was focused on road traffic in the Učka Tunnel, which has a strategic position in the national traffic system and connects the Mediterranean tourist region of Istria with Central Europe. In the context of the overall impact of road traffic on the environment, the factors influencing CO2 emissions, are examined in this paper.
The study proved the direct and indirect causal impact of tourism on traffic intensity in the Učka Tunnel and consequently, its impact on the environment through CO2 emissions. The study covered the period from 2015 to 2020, with the pandemic year 2020 obviously standing out. The analysis identified individual factors influencing the carbon footprint in the Učka Tunnel, with varying intensity. Regression analysis was used to determine the influence of the singled out factors (economic activity, tourist arrivals, tourist overnight stays, employment, unemployment, and the intensity of the pandemic) on the monthly changes in values of the tunnel’s carbon footprint throughout the year.
From a theoretical point of view, the research results clarify the cause–effect relationships between economic and social factors and road traffic in developed tourist areas. The results can be used to predict the actual environmental impacts and economic parameters that influence the management of major road infrastructure facilities. Comparing regression models 1 and 2, two variables can be singled out to predict traffic volumes and environmental impacts in normal and crises periods. The CEIZ index variable gains importance as a predictive variable in the case of major disruptions in economic development at the national level, spilling over into the regional economy. The CEIZ index can be used as a tool for managing crises in general, as well as for predicting traffic intensity in the Učka Tunnel. In contrast to the prediction of traffic volume in crises, the variable of unemployment in Istria County under normal circumstances proved to be the most stable and statistically significant for the prediction of traffic intensity and the carbon footprint of the Učka Tunnel.
The scientific contribution of the research is the filling of the existing research gap in measuring the impact of tourism on the carbon footprint segment of large transport infrastructure facilities on the environment in the operational phase of the infrastructure life cycle. The specific contribution of the research can also be noted in the expansion of the database of the actual measured data of local impacts on the environment (carbon footprints), which should provide a better (accurate) basis for environmental management in the future. The research opens the possibility of implementing the presented model in similar, mainly tourist destinations with pronounced seasonality, in order to improve the prediction process of the environmental impact and the possibilities of sustainable and crisis-resistant management of major road infrastructure facilities.
The strategic importance of interregional road connections is greater than the narrow issue of the carbon footprint associated with transport through a tunnel. However, when planning and operating infrastructure, management must balance the sustainability aspects of tunnel existence with the project profitability. Tunnels demonstrate benefits [14,17,20,21] for the connected regions by reducing travel times, mitigating regional isolation, enabling employment, and fighting population decline, as well as supporting regional economic development in general, but they must be responsibly managed. Therefore, future research on road infrastructure effects would benefit from a broader perspective, as well as an interdisciplinary approach in the research and in actual projects [31].
In relation to policy implication, the EU regulatory context will play a role in the decarbonization of transport in the near future, through measures such as the promotion of low-carbon fuels, or electric cars [55]. Actual projects demonstrate that the importance and interpretation of sustainability within a road infrastructure project are highly dependent on the interpretation of the project leader [22]. Thus, if the climate 2030 and 2050 goals are to be achieved, the integration of sustainability into major projects should not be optional nor coincidental. The EU framework for sustainable investments [31,68] requires a standardized sustainability assessment of tunnel investments, and a variety of EU policies directly or indirectly support the decrease in road transport emissions [69,70,71]. It is to be expected that the internalization of external transportation costs at the ‘polluter’ and the ‘user’ level, through carbon pricing and infrastructure charging mechanisms [71], will make a significant contribution to reducing the transport (infrastructure) CO2 emissions.
In order to reduce the size of the carbon footprint caused by the emissions in the Učka Tunnel, which are related to tourism seasonality in the Istria region, it would be desirable in the light of achieving the carbon neutral goals of the European Union 2050 plan to promote or even co-finance bus transport connections with major central European destination. It would also be ecologically justified to promote or even co-finance the local supply chains for tourism so the goods would not have to travel long distances, which include the Učka Tunnel.
The step toward a future carbon-neutral economy is not possible by “doing business as usual,” and it implies major changes. One such change could include not doing business with the cheapest suppliers, who are tied to the rest of the national market and use the supply route through the Učka Tunnel, but doing business with local and more ecologically friendly supply options. Aside from environmental aspects, infrastructural impact analysis should broaden its profitability perspective and implement criteria regarding social and ecological sustainability in relation to local stakeholders [53], as societal benefits are closely related to economic development and connectivity [48]. The singling out of measurable cause–effect relationships between economic and social factors that influence the transport-related carbon footprint in predominantly tourist areas helps distinguish the individual factors that can be used in the environmental, economic, and crisis management of major road infrastructure.
The general contribution of this paper is in raising awareness regarding the environmental impact of tourism, and in particular, tourism-related transport, in the context of the European Commission’s European Green Plan 2050 in the area of GHG emissions and the achievement of a carbon-neutral economy.
For future steps in the research, it is possible to expand the range of independent variables linking the environmental impacts of transport and tourism. Possible variables for future research can combine the economic and socio-demographic data of passengers through the tunnel (the data may be anonymously collected in collaboration with the concessionaire of the tunnel from pre-paid cards of the users). Moreover, the variables can be compared with some case studies of local tourist destinations (characteristic tourist municipalities in the region). Future research can also be broadened with data from the nearby county of Primorsko-Goranska, which is not dependent on the Učka Tunnel, but exerts some influence on the Istria region and traffic in the tunnel.

Author Contributions

Conceptualization, H.G.; methodology, H.G. and N.K.; analysis and validation, H.G. and N.K.; writing—original draft preparation, H.G. and N.K.; writing—review and editing, H.G. and N.K.; visualization, H.G.; supervision, H.G.; project administration and funding acquisition, H.G. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the Faculty of Tourism and Hospitality Management, University of Rijeka, Croatia, grant ZIP-FMTU-007-03-2022.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. National CEIZ index(es) for the period from 2015 to 2020, according to data from reference [58].
Figure 1. National CEIZ index(es) for the period from 2015 to 2020, according to data from reference [58].
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Figure 2. Unemployed and employed persons in the observed region from 2015 to 2020, according to data from references [59,60].
Figure 2. Unemployed and employed persons in the observed region from 2015 to 2020, according to data from references [59,60].
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Figure 3. Tourist arrivals and overnight stays in the observed region from 2015 to 2020, according to data from reference [61].
Figure 3. Tourist arrivals and overnight stays in the observed region from 2015 to 2020, according to data from reference [61].
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Figure 4. Monthly CO2 emissions of road traffic (in tons) for the period from 2015 to 2020 in the Učka Tunnel—calculation based in BINA Istra data (number of vehicles and vehicle categorization).
Figure 4. Monthly CO2 emissions of road traffic (in tons) for the period from 2015 to 2020 in the Učka Tunnel—calculation based in BINA Istra data (number of vehicles and vehicle categorization).
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Table
Table 1. Regression analysis of the carbon footprint of the Učka Tunnel (lnCF).
Table 1. Regression analysis of the carbon footprint of the Učka Tunnel (lnCF).
VariableModel 1,
2015–2020		Model 2,
2015–2019
Intercept12,41412,528
coefficients
Domestic tourist arrivals0.00808 *0.00423 *
Foreign tourist arrivals0.00042 *0.00045 *
Unemployed−0.04818 *−0.05752 *
CEIZ index0.03146 *0.00624 **
n7260
R20.8950.958
adj R20.8880.955
F142.23310.66
p<0.001<0.001
* p < 0.05; ** variables showing no statistical significance.
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Grofelnik, H.; Kovačić, N. Factors Influencing the Carbon Footprint of Major Road Infrastructure—A Case Study of the Učka Tunnel. Sustainability 2023, 15, 4461. https://doi.org/10.3390/su15054461

AMA Style

Grofelnik H, Kovačić N. Factors Influencing the Carbon Footprint of Major Road Infrastructure—A Case Study of the Učka Tunnel. Sustainability. 2023; 15(5):4461. https://doi.org/10.3390/su15054461

Chicago/Turabian Style

Grofelnik, Hrvoje, and Nataša Kovačić. 2023. "Factors Influencing the Carbon Footprint of Major Road Infrastructure—A Case Study of the Učka Tunnel" Sustainability 15, no. 5: 4461. https://doi.org/10.3390/su15054461

APA Style

Grofelnik, H., & Kovačić, N. (2023). Factors Influencing the Carbon Footprint of Major Road Infrastructure—A Case Study of the Učka Tunnel. Sustainability, 15(5), 4461. https://doi.org/10.3390/su15054461

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