Greenhouse Gas Emissions from Road Transport and Their Economic Value in the Assessment of Transport Projects Using a Cost–Benefit Analysis: Approaches Implemented in the Slovak Republic and Selected Central European Countries

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The proposed measures for the modification and supplementation of the CBA methodology in the Slovak Republic in the field of GHG emission assessments after their implementation can objectify the CBA results for this sector and can bring more realistic results for the process of assessing the implementation of transport construction in road transport.

Abstract

This comparative analysis identified disproportions in the CBA methodologies of selected countries in the scope of GHG emissions and their economic value in assessing transport projects in Slovakia and selected Central European countries. This study identifies the disparities in CBA methodologies in the Slovak Republic in the field of greenhouse gases. It proposes specific measures for improving the methodology itself, the use of best practices from CBA methodologies in selected countries, and discusses the possible implementation of the latest standards in the field of greenhouse gases and their economic value. These steps can objectify the calculated economic value of climate change for policymakers and decision-makers on transport infrastructure investments. The proposed measures for the modification and supplementation of the CBA methodology in the Slovak Republic in the field of GHG emission assessments after their implementation can objectify the CBA results for this sector and can bring more realistic results for the process of assessing the implementation of transport construction in road transport. The paper contains a case study for the calculation of GHG emissions from road transport, their economic value, and their disproportion in case of changes in the CBA methodology in the Slovak Republic for the assessment of road transport projects.

1. Introduction

A cost–benefit analysis (CBA) is a tool for the economic evaluation of the effectiveness of project implementation according to the financial expression of the costs and benefits arising from the project. Due to its focus, the CBA is also intensively applied in the transport sector. The transport system should be able to use resources more efficiently and increase its competitiveness [1]. The various factors and their interconnections make it difficult to accurately understand all possible interactions within transport projects [2]. The CBA methodologies of individual countries are not unified. The purpose of this paper is to analyze and evaluate to what extent they apply uniform and current emission factors, also whether they apply the same principles and procedures for the financial expression of the costs of climate change. This is even more important in the application of a CBA in the assessment of road transport constructions, as the upstream road infrastructure is being built along the routes of European transport corridors. According to Hajduk and Poliak [3], the European Union has the densest transport network in the world and has a much better-developed infrastructure per 100 km² than the United States and not much worse than Japan. Challenges in the transport sector in the European Union include creating a well-functioning Single European Transport Area; connecting Europe with modern, multimodal, and safe transport infrastructure networks; and moving toward low-carbon mobility, which includes reducing other negative transport externalities. From a social point of view, the affordability, reliability, and accessibility of transport are key. The results of the CBA analysis influence the decision-making processes for road infrastructure construction. Disparities in CBA methodologies between European countries may jeopardize the completion of the superstructure along the routes of international transport corridors.

The aim of this paper is to present the identified disproportions in the CBA methodology for a post-assessment of transport projects in the Slovak Republic with a focus on GHG emissions in comparison with selected Central European countries. The findings result from a research project aimed at the analytical evaluation of the Slovak methodology of a cost–benefit analysis (CBA) compared to foreign methodologies for the post-judgment of linear transport constructions and the proposal of possible adjustments of selected parameters. A partial research objective is a comparative analysis of the CBA methodology in Slovakia with the methodologies of selected Central European countries in the field of GHG emissions and climate change costs. The identified differences, assessments of relevance, and suitability are to serve in the form of recommendations for improving the applied approaches for calculating GHG emissions and climate change costs. The reason for comparing the CBA methodology in the Slovak Republic with the methodologies of selected Central European countries is the common historical and economic development, as well as the high interstate mobility of people and exchange of goods using the superior trans-European transport infrastructure. The impulse for the comparative analysis and this research project was the fact that in the case of the assessment of selected transport projects in the Slovak Republic by the CBA methodology, an economic disadvantage was determined, but if the parameters of the CBA methodologies of the neighboring countries were applied, the project could be economically advantageous. Therefore, the research assumption was made that there are differences in the CBA methodologies in the Slovak Republic in the GHG area concerning selected Central European countries, with an emphasis on their concretization, identification of the suitability/unsuitability of the procedures for calculating the costs of climate change, and the parameters applied.

The findings and recommendations can be a basis for designing CBA methodologies for GHG transport projects in EU countries that do not yet have methodologies in place and for updating existing CBA methodologies. Outdated parameters may lead to results such that decisions to support transport projects, even of international (transnational) importance, may not be made.

2. Literature Review

2.1. Cost–Benefit Analysis

De Rus et al. [4] have conducted research on cost–benefit analyses (CBAs) of transport projects, with an emphasis on theoretical frameworks, practical guidelines, and the measurement of direct effects, shadow prices, and wider economic benefits (WEBs). Their research highlights the key drivers of an economic evaluation, such as time savings, a reduction in operating costs, and quality improvements. At the same time, they offer a simple model to avoid common measurement errors. Guidelines for measuring direct effects focus on consistency and avoiding errors. The practical rules for shadow prices emphasize the need to adjust market prices for social costs. Similar research has been conducted by Jones et al. [5]. Nahmias-Biran and Shiftan [6] discuss the development of an innovative and comprehensive criterion for evaluating transport projects with a focus on equity aspects. The authors propose using activity-based models (ABMs) and subjective well-being measures (SWBs) to assess the full benefits of transportation projects and calculate accessibility improvements. They introduce a new measure called the “Subjective Value of Accessibility Benefits” (SVOA) that combines the ABM measure of accessibility with SWBs to provide a single measure that supports both equity and efficiency considerations when comparing alternatives.

Damart and Roy [7] examined the use of a cost–benefit analysis (CBA) in transport infrastructure decision-making in France. They emphasize that the CBA helps public decision makers to determine investment priorities, and it is essential to consider not only financial factors but also intangible factors such as noise and safety. Stakeholder participation is crucial for effective decision-making to consider different aspects. The research underlines the need for the transparency and accessibility of the CBA process and highlights its importance for transport investment and inclusive decision-making in France. Similar research has also been conducted by Vagdatli and Petroutsatou [8] and applied to a highway project in Greece. Gössling and Choi [9] examine the use of a cost–benefit analysis (CBA) by public transport authorities (PTAs) in Copenhagen, which appears to be the only city in the world justifying investments in bicycle infrastructure using a CBA. As the example of Copenhagen shows, reaching a political consensus on the parameters to be included, as well as their unit costs, is a key factor in the success of a CBA. Gerbec et al. [10] analyzed the impact of different drives on urban buses using a CBA of the CIVITAS-ELAN project in Ljubljana. The results of the updated cost–benefit analysis using the available data confirm that the reliability of the analysis depends significantly on the data used or its forecast.

Research by Bert van Wee [11] looks at the ethical aspects of a cost–benefit analysis (CBA) in the evaluation of transport projects and policies. The research discusses the criticisms that a CBA faces, such as limited applicability, problems with indicator selection, and ignorance of distributional effects. It proposes ways to address the ethical shortcomings of a CBA and highlights the importance of considering distributional effects and ethical theories in the evaluation. Rothengatter [12] explores the concept of wider economic impacts (WEIs) in evaluating transport infrastructure investments. He underlines the importance of considering WEIs alongside direct impacts in a cost–benefit analysis (CBA). He points out the need for a comprehensive assessment of infrastructure investments, considering social needs and technological innovation. Similar research has also been conducted by Vigren and Ljungberg [13].

Browne and Ryan [14] address the evaluation of transportation policies and programs in their research using a variety of techniques, including a cost–benefit analysis (CBA), cost–effectiveness analysis (CEA), and multi-criteria decision analysis (MCDA). The authors identify problems with quantifying non-market impacts and monetizing the total costs and benefits of transportation policies. They conclude that a CEA and CBA are useful for estimating costs and benefits but are limited in evaluating policies with marginal costs or multiple benefits. Hickman and Dean [15] claim that the application of a quantitative assessment of the various impacts of complex transport projects can only be partial in a cost–benefit analysis. The analysis may overlook impacts on society, human life, the environment, and the built environment. According to Wolek et al. [16], in terms of public transport decision-making, the recommended method for selecting the optimal investment scenario is the multi-criteria analysis (MCA). It allows the inclusion of various differentiated impacts that cannot be easily valued, which is its advantage over the CBA. However, the CBA is also recommended as a complementary method for the optimal investment scenario compared to the reference scenario. Andersson et al. [17] address the challenges in estimating the effects of disruptions in freight transport and propose a model to estimate the value of transport time variability (VTTV). They identify four main types of disruptions and investigate methods to measure transport time variability, specifically VTTV. They propose a mathematical method for estimating VTTV for freight transport and conclude that the chosen VTTV measure should capture the properties of the transport time probability distribution.

Vignetti et al. [18] combined a retrospective CBA with a qualitative analysis. Their research, carried out in nine European countries, highlights positive economic effects such as time and operational cost savings, while also demonstrating the importance of considering social exclusion (SE) and wider economic impacts when evaluating projects.

A CBA of traffic and transport projects also includes their environmental impacts and financial implications. Different approaches to calculating GHG emissions, emission patterns, and unit costs of GHGs lead to divergent results in assessing road transport developments in individual countries, which are often transnational in character and part of an international transport network. The varying approaches of countries and the results of the CBA affect prioritization, as well as the approval of the construction of transport structures. In the case of international transport corridors running through several countries, this disparity can compromise their integrity.

In EU countries, the Guide to Cost–Benefit Analysis of Investment Projects, the latest version from 2014, is used to assess transport infrastructure projects. The Guide is an operational manual that supports the Evaluation Unit and the geographical units of DG Regional Policy, other Commission services, and Member States in need to assess and check the completeness and adequacy of applications for EU funds received by the applicant. The guide is mandatory for all major projects submitted under the 2014–2020 ESIF. The Economic Appraisal Vademecum (EAV) was published in 2021. The EAV aims to support and simplify economic appraisal for EU co-funded investments in the programming period of 2021–2027. The EAV in Annex I provides an overview of existing CBA manuals at the national level; specifically, in 16 EU countries, there are 22 manuals focusing on transport.

To date, no research has been conducted in the Slovak Republic on comparing CBA procedures for assessing transport projects with an emphasis on GHG emissions and climate change costs, including the identification of disparities and an assessment of the adequacy of calculations. It is precisely the issues of climate change and transport that have received considerable attention recently.

2.2. Environmental Impact

Dehnhardt et al. [19] examined the use of a cost–benefit analysis (CBA) in policymaking, with an emphasis on a case study of climate change adaptation in Bremen, Germany. A CBA is seen as useful in raising awareness of environmental assets and increasing the transparency of the policy-making process. The research identifies factors that facilitate or constrain the integration of a CBA into policy-making, such as the participatory process of conducting a CBA, knowledge building, and time and resource constraints. J. Leicht and M. Leicht [20] provide an overview of the relationship between climate change (CC) and transport companies (TC), with an emphasis on sustainable transport practices and TC adaptation strategies. The research identifies four macro themes: climate impacts on transport companies (ICTC), climate impacts of transport companies (ITCC), climate-related regulations and TC reporting, and sustainable strategies of transport companies.

Banar and Özdemir [21] analyzed the environmental and economic aspects of passenger rail transport in Turkey using life cycle assessment (LCA) and life cycle costing (LCC) methods. The research focuses on high-speed rail (HSR) and conventional rail (CR) systems and their environmental and cost impacts. HSR has a higher environmental impact due to infrastructure (58%) and operations (42%), while for CR, they are 39% and 61%, respectively. The environmental factors examined include abiotic depletion, acidification, eutrophication, global warming, human toxicity, and freshwater ecotoxicity.

Research conducted by Pal et al. [22] deals with the development of an assessment framework using three techniques—simple additive weighting (SAW), interpretive structural modeling (ISM), and interpretive rating process (IRP)—to analyze transport and its impact on climate change. The authors introduce Ecological Modernization Theory (EMT) and describe a three-stage hybrid approach that uses SAW to reduce transport factors and measures to critical factors, ISM to examine the relationships between them, and IRP to rank them.

Rehman et al. [23] investigated the impact of green transport on environmental sustainability in ten countries that have undergone an energy transition. The authors highlight the critical role of transport in greenhouse gas emissions and environmental degradation. They use a sophisticated econometric technique, quantiles through moments, to develop a green transport index and analyze the data. The research also examines the impacts of innovation, domestic investment, urbanization, and the quality of institutions on the ecological footprint. The results suggest that innovation, domestic investment, and institutional quality contribute to maintaining environmental quality, while urbanization increases the ecological footprint. The simulation results of Lajunen [24] using a cost–benefit analysis suggest that plug-in hybrid and electric city buses have the best potential to reduce energy consumption and emissions. However, when selecting hybrid and electric city buses for fleet operation, it is essential to consider the operating schedule and route planning.

When applying both environmental and climate change impacts in CBAs, different approaches and the structure of pollutant emissions, including greenhouse gas emissions, are applied. Most global emissions come from the combustion of fossil fuels, which releases carbon dioxide (CO₂) into the atmosphere. In addition to CO₂, emissions also come from other greenhouse gases, namely, methane (CH₄) and nitrous oxide (N₂O). Although CH₄ and N₂O emissions are smaller in the atmosphere, they have a more substantial impact on the climate. Individual gases have been assigned weighted values based on their potency as greenhouse gases to simplify the accounting of greenhouse gases. This potency is referred to as the global warming potential (GWP), and their standard unit is the carbon dioxide equivalent or CO₂e [25].

Effective emission reduction strategies must consider different greenhouse gases (GHGs), such as CO₂, N₂O, and CH₄ [26]. These gases have different abilities to heat the atmosphere per unit mass and vary in their persistence in the atmosphere. Therefore, a key element is the framework for multiple greenhouse gases that determines the exchange ratios between them. The Kyoto Protocol introduced the 100-year global warming potential (GWP) as a metric to convert CH₄, N₂O, and fluorinated gases (F-gases) to CO₂ equivalents, which is proposed in the research of Lashof and Ahuja [27] and updated in the IPCC assessments (for the most recent values, see [28]). This method reduces the mitigation costs through flexibility in reducing the emissions of different GHGs. The EMF21 study compared multi-GHG strategies with CO₂-only strategies and found significant cost reductions in achieving the same target if a multi-GHG strategy was applied [29].

Meunier and Quinet [30] discussed the assessment of GHG emissions and the uncertainty associated with the cost–benefit analysis (CBA) of transport projects. They outline the importance of accurately and objectively including the impact of GHG emissions in the CBA, given the growing role of the transport sector in GHG emissions. The research discusses the evolution of CO₂ values in France and proposes a more representative indicator to compare national CBA methods. Jereb et al.’s [31] research quantifies fuel consumption and CO₂ emissions based on real traffic data at an intersection. The research was conducted in the Slovenian city of Celje and aimed to identify approaches to reduce the environmental and economic impacts of traffic operations through proper traffic flow management.

Liaquat et al. [32] looked at the potential for reducing emissions in the road transport sector in developing countries through biofuels. The research conducted by Liu et al. [33] focuses on analyzing the impact of the introduction of fuel cell vehicles (FCVs) into the on-road vehicle fleet in China on greenhouse gas (GHG) emissions. The research conducted by Krause et al. [34] analyzed the options for reducing CO₂ emissions in European road transport by 2050, with a focus on measures to improve vehicle efficiency and to consider the emissions of electric vehicles (EVs).

2.3. Direct and Indirect Emissions

In transport, approaches to calculating pollutants and greenhouse gases fall into two basic groups in terms of the direct or indirect environmental impact. Direct emissions are represented by the tank-to-wheel (TtW) approach, and indirect emissions by the well-to-tank (WtT) approach. The well-to-wheel (WtW) approach is a more comprehensive approach considering both direct and indirect emissions, but it does not deal with emissions over the entire life cycle of the product.

Research by Vagdatli and Petroutsatou [8] focuses on estimating tank-to-wheel efficiency functions for different vehicle types, such as internal combustion engine vehicles (ICEVs) and battery electric vehicles (BEVs). The study addresses the limitations of using a constant value to represent TtW efficiency, which may not adequately capture the variability of driving conditions. Hjelkrem et al. [35] found that TtW efficiency varies depending on the engine power used, and the estimated functions exhibited different patterns for diesel, petrol, and electric vehicles. The results showed that the TtW efficiency for electric vehicles was higher than that for fossil fuel vehicles, reaching approximately 85% efficiency. For fossil fuel vehicles, the efficiency varied with engine power, with diesel vehicles showing higher efficiency than gasoline vehicles at low power levels. Ebrahimi et al. [36] conducted research on emissions from articulated wheel loaders, which are non-road mobile machines used in the construction industry.

The research conducted by Osorio-Tejada et al. [37] deals with the environmental assessment of road freight transport services and presents a methodological approach to defining boundaries and activities within the transport system. It highlights the importance of integrated analyses to document the environmental sustainability of services, pursue policy objectives, and enable consumers to choose the most sustainable services. The study reviews previous life cycle assessment (LCA) studies in the transport sector and identifies limitations in the assessment of individual transport components.

Ramachandran and Stimming [38] looked at a comparison of low-carbon alternatives for road transport, such as electricity, hydrogen, and biofuels, in combination with battery electric vehicles (BEVs) and fuel cell electric vehicles (FCEVs). The comparison is based on the overall efficiency and greenhouse gas (GHG) emissions involved in converting primary energy sources into the energy needed on wheels through a well-to-wheel analysis. The research considers factors such as the electricity generation mix, renewable energy sources, and the impacts of direct ethanol fuel cells (DEFCs) on GHG emissions and the overall efficiency of the chain.

In research conducted by Alamia et al. [39], an analysis of WtW biomethane derived from biomass gasification for use in heavy-duty engines in the European Union was carried out. The research compared biomethane with fossil fuel alternatives such as compressed natural gas (CNG), liquefied natural gas (LNG), and diesel. Three different modern gas engines for heavy-duty vehicles were also considered: the spark ignition (SI), the dual fuel (DF), and the high-pressure direct fuel injection (HPDI) engines. The WtT research was based on a case study of the GoBiGas plant in Gothenburg, Sweden, which is the largest biomethane plant in the world. In the TtW part, three different engine technologies were compared. The results showed that WtW emissions from biomethane were reduced by 60–67%, 43–47%, and 64% when used in SI, DF, and HPDI engines, respectively, compared to diesel. HPDI and DF engines were found to be the most efficient technologies for biomass utilization, achieving significant emission reductions.

The research by Thiel et al. [40] analyses the potential costs and impacts of achieving CO₂ emission targets for new vehicles in the EU. The research focuses on TtW emissions and examines scenarios involving electric drive vehicles (EDVs) and shifts between vehicle segments. In their research, Correa et al. [41] evaluated five types of powertrains: diesel, hybrid, compressed natural gas enriched with hydrogen, proton exchange fuel cell, and battery electric vehicles. The analysis is divided into two stages: well to wheel and tank to wheel. Different driving cycles, ranges, and energy scenarios for electricity and hydrogen production are considered in the research.

2.4. Evaluation of Greenhouse Gases

Several approaches and different unit cost values are applied to evaluate greenhouse gases. In the current literature on the monetary valuation of climate impacts, two main approaches are found [42,43,44]. These approaches are based on economic theory and practice. One focuses on estimating the costs to society of climate change, while the other focuses on the costs of reducing CO₂ or other greenhouse gas emissions. The former approach is often referred to as the social cost of carbon (SCC), while the latter is known as the marginal abatement cost (MAC), which is expressed as an incremental change [45].

CORINAIR (Core Inventory Air), endorsed by the European Environment Agency (EEA), is an emissions calculation methodology that is consistent with IPCC guidelines and used for national and regional environmental assessments [46]. Emissions trading forms a key part of the EU’s policy to combat climate change. The debate on the inclusion of the transport sector has been going on for a long time, and since 2012, air transport has been included. The cost of reducing carbon dioxide emissions from the transport system is considered higher compared to sectors currently included in the Emissions Trading System (ETS) [47,48,49].

According to Poliak et al. [50], the direction of transport and the associated use of specific road infrastructure along the route of transport in international road freight transport have major impacts on the price of transport and price competitiveness in road transport in the EU common market.

The basic inputs for the software are environmental and emission factors, engine types, and fuel specifications. In addition, one of the other important parameters is the age of the vehicle, given that older vehicles with longer mileage pollute more, hence, the ’mileage degradation’ factor. This factor is used to relate the age of the vehicle or the annual mileage to another resulting emission degradation factor [51]. For EURO I and EURO II passenger cars with mileage above 80,000 km, a 60% increase in CO and NOx emissions and a 30% increase in NMVOC emissions can be observed [52]. In terms of the emission estimation, omitting specific parameters to calculate its effects leads to underestimating the problem. Most software and models, such as COPERT, do not allow the calculation of a mileage degradation factor specifically for buses. However, iGREEN is very useful not only when mileage degradation is an evident characteristic of the fleet but also whenever operating conditions are affected by different driving environments and weather situations [51].

3. Materials and Methods

The research and analyses are based on the currently valid CBA methodologies for assessing transport projects in the Slovak Republic, the Czech Republic, Hungary, and Austria. These methodologies contain specific GHG emission characteristics, emission factors, and unit costs of climate change, which are used in the analytical and research parts of this paper.

• The values of GHG emission factors and densities of selected fuels according to the Handbook of Emission Factors for Road Transport (HBEFA Methodology), version 4.2.2 were also used [53].
• The unit costs according to the Handbook on the External Costs of Transport, version 2019, January 2019—V1.1, European Commission [54], were used to determine the financial value of GHG emissions.
• Emission and energy factors for greenhouse gas emissions were calculated according to ISO 14083 Greenhouse gases—Quantification and reporting of greenhouse gas emissions arising from transport chain operations, ISO—International Organization for Standardization, valid from March 2023 [55].
• Emission and energy factors for greenhouse gas emissions were calculated according to STN EN 16258 Methodology for the calculation and declaration of energy consumption and greenhouse gas emissions from transport services (freight and passenger transport), Slovak Institute of Technical Standardization, September 2013 [56].

3.1. CBA Methodology in the Slovak Republic—Characteristics of Greenhouse Gas Emissions, Their Production, and Economic Value

According to the CBA methodology in the Slovak Republic, the relevant greenhouse gases from transport (arising from the combustion of fuels) to be considered in the CBA are carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O).

As a first step, the processor should determine the amount (ideally in tons) of greenhouse gases emitted based on fuel consumption data for vehicles using traditional fuels (petrol and diesel) and emission factors from electricity consumption (in the case of electric drives). Emission factors for different vehicle categories are in

Table 1. Emission factors (g/kg) of road vehicles (conventional fuels) [57,58].

Vehicle Category (Fuel)	Polluting Substance
	CO2	CH4	N2O
Passenger vehicles (petrol)	3180	1.09	0.206
Passenger vehicles (diesel)	3140	0.23	0.087
Light-goods vehicles (diesel)	3140	0.16	0.056
Heavy-goods vehicles, medium goods vehicles, and buses (diesel)	3140	0.27	0.051

below.

The density of the different fuels given in the CBA methodology in the Slovak Republic, as well as the emission factors according to the CBA methodology in the Slovak Republic, were used to calculate the amount of greenhouse gases emitted by petrol and diesel vehicles correctly. The data source for the CBA methodology in the Slovak Republic is the EEA.

Based on the content of the CBA methodology in the Slovak Republic, we have defined relationships for the calculation of the quantity of fuel consumed, the quantity of pollutants, and the cost of pollutants in Supplementary Materials.

The quantity of fuel consumed I (by mass) is calculated using Equation (S1) from Supplementary Materials.

The amount of greenhouse gases from road transport i is calculated using Equation (1):

$${AGHGRT}_i={AFCM}_i\ast {EFGHG}_{ik}$$

(1)

where

• ${AGHGRT}_i$ is the amount of greenhouse gas from road transport.
• ${EFGHG}_{ik}$ is the emission factor of the i-th type of fuel of the k-th type of GHG.

Substituting Equation (S1) into Equation (S2), we obtain Equation (S3) from Supplementary Materials.

The GHG cost of road transport is calculated using Equation (2):

$${CGHGRT}_{ik}={AGHGRT}_{ik}\ast {UCGHGRT}_{ik}$$

(2)

where

• ${CGHGRT}_{ik}$ is the cost of the kth type of greenhouse gas from the consumption of the i-th type of road transport fuel.
• ${UCGHGRT}_{ik}$ is the unit cost of the kth type of greenhouse gas from the consumption of the i-th type of fuel in road transport.

Substituting Equation (S3) into Equation (S4), we obtain Equation (S5) from Supplementary Materials.

To calculate the amount of greenhouse gases emitted by electric vehicles, the CBA methodology in the Slovak Republic uses emission factors according to the European Investment Bank (EIB) methodology, which is dedicated to projects and their carbon footprint. In this case, greenhouse gas emissions are considered indirect, i.e., they are not directly generated by the electricity consumption of the project (vehicles) but reflect the carbon footprint associated with the production and distribution of electricity. The factors are expressed in grams of CO₂ per kilowatt-hour and are specific to the Slovak Republic, as defined in

Table 2. Emission factors (gCO₂/kWh) of electricity consumption [58,59].

High-Voltage Network (HV)	Medium-Voltage Network (MV)	Low-Voltage Network (LV)
206	210	216

.

The valuation includes a unit price for CO₂ only. Therefore, the methodology converts other greenhouse gases into so-called carbon dioxide equivalents (CO₂es). Non-CO₂ greenhouse gas emissions are multiplied by a potential global warming factor:

• CO₂e (tons) = CO₂ (tons) × 1;
• CO₂e (tons) = CH₄ (tons) × 25;
• CO₂e (tons) = N₂O (tons) × 298;

The climate impacts of CH₄ and N₂O emissions are much higher than CO₂ alone. As GHG emissions have a global impact, the same price per ton of CO₂es is recommended for all countries, as can be seen in

Table 3. Unit price of t CO₂es in EUR at the 2023 price level [58,60].

2024	2025	2030	2035	2040	2045	2050
183.3	230.8	349.8	545.6	734.5	923.4	1119.2

. This is set based on the EIB recommendation as the median of various international models seeking to socially price the shadow costs in relation to strategic climate change mitigation objectives. The unit price increases significantly over time and is adjusted to the 2023 price level.

The Annex of the CBA methodology provides a detailed (annual) trend of the unit cost per ton of CO₂es for the purpose of the CBA processing. The unit cost of CO₂es is no longer adjusted for GDP growth or elasticity.

3.2. CBA Methodology in Hungary—GHG Emission Characteristics, Production, and Economic Value

In Hungary, the subject is addressed in Chapter “8.3.2 Economic Benefits” of the Methodological Guide to Cost–Benefit Analysis of Transport Projects, in the section “Changing Climate Change Impacts” [61].

The cost of greenhouse gas emissions is calculated using Equation (3):

$$Thecostofgreenhousegasemissions=A_{GHG}\ast P_{GHG}$$

(3)

• $A_{GHG}$ is the change in the amount of greenhouse gas emissions caused by the project in CO₂ equivalents (ton CO₂es), and
• $P_{GHG}$ is the shadow price of CO₂ equivalents (HUF/ton of CO₂es).

GHG emissions from transport projects are analyzed mainly based on the consequences of project activities (impact areas 2 and 3), such as vehicles operating on transport infrastructure. The base for calculating relative GHG emissions is based on passengers switching from one mode to another (mode-switching impacts), passengers changing mode (switching from one route to another or from one part of the day to another), and the increased number of passengers/transportations generated.

The required inputs are the change in greenhouse gas emissions expressed as CO₂ equivalents (CO₂e tons/year),

• Unit environmental external costs (HUF/ton CO₂e).

A separate climate impact analysis will provide data on the change in emissions (in tons/year). Monetary values of unit CO₂ equivalent emissions (CO₂es) have been determined based on European Investment Bank (2013) data, of which a median value shown in

Table 4. The unit cost of climate change (HUF/tons CO₂es) at the 2017 price level [61].

EIB Median (2013)
7560 HUF/ton CO2e (EUR 18.4278/ton CO2e)

Note: Conversion to EUR currency according to the ECB and NBS exchange rate list as of 5 November 2024: 1 EUR = 409,25 HUF.

below is recommended.

The annual growth rate of the actual unit cost value equals the change in real GDP (see

Table 5. GDP growth rate estimate [61].

	2017	2018	2019	2020–2030	2031
GDP growth rate (%)	103.6%	103.7%	103.2%	102.6%	101.5%

below).

In the absence of a separate climate impact analysis, the monetary value of the GHG-related impact can be estimated using the following inputs:

• Change in the number of kilometers traveled (vehicle-km/year);
• Unit CO₂ equivalent emissions (tons CO₂es/km);
• Unit external environmental costs (HUF/tons CO₂es).

In this case, the change in kilometers must be provided by a traffic model or traffic estimates. Data for 2010 on the average unit CO₂ emissions from road vehicles can be found, for example, in the update of the DG-MOVE manual (2014) (see also

Table 6. Unit CO₂e emissions of road vehicles (g CO₂e/km) in the CBA methodology in Hungary [61].

Vehicle Category	Diesel	CNG	Petrol	LPG	All Fuel Types
Bus	676	528			670
Passenger vehicle	179	159	197	182	189
Light commercial vehicle	218		278		228
Trucks 3.5–7.5 t	312				312
Trucks 7.5–16 t	534				534
Trucks 16–32 t	715				715
Trucks > 32 t	906				906
Moped			59		59
Motorcycle			104		104

).

The calculation of the amount of CBA CO₂e emissions in Hungary produced during transport is calculated according to Equation (S7) from Supplementary Materials:

$${ACO}_{2}eRT={EFCO}_{2}eVi\ast {DTV}_j$$

(4)

where ${EFCO}_{2}eVi$ is the emission factor of the i-th fuel type, and ${DTV}_j$ is the distance traveled by the j-th vehicle category.

If detailed data on the composition of road vehicles in the area of influence are available, DG-MOVE (2014) provides valuable data by vehicle category, fuel, and EURO engine class. Any source dealing with unit GHG emissions can only be used if sufficiently substantiated and detailed.

Based on JASPERS: GHG Emission Assessment for Road and Rail/Public Transport Projects (2015), the basic calculation principles are as follows. For each option, the factors of the mileage data and the emission data in carbon dioxide equivalents must be calculated.

• In the case of public road transport, the total kilometers traveled is the number of kilometers traveled over a certain period of time.

  ○

  The emission factor depends on the fuel consumption, the relevant speed, the road and vehicle category, as well as the road quality and geometry.

• In the case of public transport, the number of kilometers traveled is equal to the volume of kilometers traveled per year (vehicle km or train km).

  ○

  In terms of emission factors for tram, rail, and trolleybus transport,

  •

  energy consumed per kilometer (kWh/vehicle-km or kWh/vehicle-km);

  •

  the emission factor calculated in carbon dioxide equivalent (t CO₂/KWh) must be used.

  ○

  In the case of public bus transport,

  •

  the calculation is the same as for public road transport.

3.3. CBA Methodology in Austria—GHG Emission Characteristics, Production, and Economic Value

The subject is addressed in Chapter “9.4.5 Environmental costs” of the document Cost-Benefit Analysis in Transportation 2010, in the section “Climate costs”. Climate costs consider the currently assumed causal relationship in the CBA methodology in Austria between increased CO₂ emissions and an increase in the average atmospheric temperature, which is assumed to lead to macroeconomic damages compared to the desired (past) average atmospheric temperature (ceteris paribus) [62].

The starting point for determining the climate cost of road transport is the mass of fuel consumed [t], which is multiplied by a factor of 3.15 to obtain the mass of CO₂ emissions produced [t]. At a CO₂ cost rate of EUR 50/t (2009 price level), multiplying by the mass of CO₂ emitted gives the climate protection cost.

The greenhouse gas cost (climate protection cost) of road transport is calculated using Equation (5):

$${CCO}_{2}RT={ACO}_{2}RT\ast {UCCO}_{2}RT=AFC\ast {EFCO}_2\ast {UCCO}_{2}RT$$

(5)

where

• ${CCO}_{2}RT$ is the greenhouse gas cost of road transport fuel consumption (EUR),
• ${ACO}_{2}RT$ is the amount of CO₂ emissions produced from road transport (tons of CO₂)
• ${UCCO}_{2}RT$ is the unit cost per tone of CO₂ production from road transport (EUR/1 tons CO₂),
• $AFC$ is the amount of fuel consumed in road transport (tones), and
• ${EFCO}_2$ is the CO₂ emission factor (3.15 t CO₂/1 t fuel).

Separate studies are needed for the increased use of non-fossil fuel energy (e.g., hydropower for trolleybuses, trams, or railways).

3.4. CBA Methodology in the Czech Republic—GHG Emission Characteristics, Production and Economic Value

The topic is addressed in chapter “8.1.14 Externality” of the document Revision of the Departmental Methodology for the Evaluation of Economic Efficiency 2022, in the section “Environmental Pollution” [63].

Changes in pollution are calculated using the incremental method as the product of the change in pollutants in tons per year and the unit value of the social cost of the pollutant in a given year.

The greenhouse gas cost of road transport is calculated using Equation (6):

$$CGHGRT=AGHGRT\ast UCGHGRT$$

(6)

where

• $CGHGRT$ is the cost of greenhouse gases from road transport (CZK),
• $AGHGRT$ is the amount of greenhouse gases from road transport (tones), and
• $UCGHGRT$ is the unit cost of greenhouse gases from road transport (CZK/ton).

For road freight transport, Equation (S9) takes the form of Equation (S10) from Supplementary Materials, taking into account the type of vehicle and the driving performance.

The summary

Table 7. Emission factors of observed pollutants in passenger transport in the CBA methodology in the Czech Republic (g/vehicle-km) [59,63,64].

Mode of Transport/Unit	Type of Transport	Emission Factor
		CO2	NOX	SO2	PM2.5	PM10
Road transport (g/vehicle-km)	IAT—average	180.000	0.512	0.006	0.029	0.051
	IAT—city	240.000	0.683	0.007	0.039	0.068
	BUS—long-distance	783.000	4.779	0.051	0.098	0.942
	BUS—city	862.000	5.261	0.057	0.108	1.038
Rail transport (g/train-km)	Diesel—regional	1848.000	0.206	0.002	0.337	1.987
	Diesel—long-distance	976.000	1.089	0.009	1.781	10.500
	Electro—regional	2766.000	0.017	0.000	0.032	0.188
	Electro—long-distance	6915.000	0.043	0.000	0.080	0.469
Air transport (g/flight-km)	Domestic	6612.000	2.107	0.017	0.246	0.000
	International	23,251.119	7.410	0.059	0.865	0.000

Notes relating to Table 7 can be found in the Supplementary Materials.

and

Table 8. Emission factors of observed pollutants in freight transport in the CBA methodology in the Czech Republic [59,63,64].

Mode of Transport/Unit	Type of Transport	Emission Factor
		CO2	NOX	SO2	PM2.5	PM10
Road transport (g/vehicle-km)	Light DV	241.000	0.694	0.002	0.045	0.059
	Heavy GV	604.000	7.626	0.027	0.202	0.111
Rail transport	Diesel	11,434.000	4.353	0.035	6.957	89.301
	Electricity	7657.722	0.204	0.002	0.366	4.700
Air transport (g/flight-km)		6612.000	32,550.000	10.374	0.083	1.211
Water transport (g/sail km)		23,251.119	23,909.450	370.100	2.946	10.700

Notes relating to Table 8 can be found in Supplementary Materials.

below show other pollution cost metrics, but also the cost of greenhouse gas (CO₂) emissions. Where more detailed calculations are not available, simplified emission factors broken down by mode of transport and transport type can be used to quantify the most important pollutants.

Greenhouse Gas Emissions and Their Economic Value—CBA Methodology in the Czech Republic

The topic is addressed in chapter “8.1.14 Externality” of the document Update of the Departmental Methodology for the Evaluation of Economic Efficiency 2022, in the section “Costs from Greenhouse Gas Emissions”.

To quantify the social cost of GHG emissions, the following steps are recommended:

1

Determining the amounts of additional tons of CO₂, N₂O, and CH₄ emitted or saved (e.g., using project-specific emission factors, depending on the mode and transport type, average speed, and traffic density, expressed in grams per 1000 vehicle-km) or the amount of additional CO₂, N₂O, CH₄ emitted or saved;

2

Conversion of all GHG quantities from step 1 to CO₂ equivalents (CO₂es)

• CO₂e (tons) = CO₂ (tons) × 1;
• CO₂e (tons) = CH₄ (tons) × 25;
• CO₂e (tons) = N₂O (tons) × 298;

3

Quantification of costs using unit costs per ton of CO₂es.

Due to the global impact of GHG emissions, the same unit cost of EUR 90 per ton CO₂es is recommended for all countries (recommended value for 2010, “Updated Guide on External Costs of Transport”, RICARDO-AEA, Report to the European Commission, Directorate-General for Transport and Mobility, January 2014). This valuation is valid when expressing the cost of GHG emissions before 2022.

Following the recommendation formulated in the 2021–2027 Technical Guidance on Climate Impact Screening of Infrastructure, the unit costs resulting from the shadow carbon prices published by the EIB as the best available estimate of the cost of meeting the temperature increase limitation target set in the so-called Paris Agreement are then considered for all subsequent years from 2022 onwards inclusive. The shadow carbon price values for each year are shown in

Table 9. Unit cost of CO₂es from and including 2022 (CZK/ton), CU 2017 [63,65].

Year	CZK/ton CO2es	EUR/ton CO2es	Year	CZK/ton CO2es	EUR/ton CO2es
2022	3128	123.43	2038	12,924	509.96
2023	3594	141.81	2039	13,665	539.20
2024	4061	160.24	2040	14,405	568.40
2025	4527	178.63	2041	15,146	597.64
2026	4994	197.06	2042	15,887	626.88
2027	5460	215.44	2043	16,628	656.12
2028	5927	233.87	2044	17,369	685.36
2029	6393	252.26	2045	18,110	714.60
2030	6860	270.69	2046	18,878	744.90
2031	7628	300.99	2047	19,646	775.20
2032	8396	331.29	2048	20,414	805.51
2033	9165	361.64	2049	21,183	835.85
2034	9933	391.94	2050	21,951	866.16
2035	10,701	422.25	2051	21,951	866.16
2036	11,442	451.49	2052	21,951	866.16
2037	12,183	480.72	2053	21,951	866.16

Note: Conversion to EUR currency according to the ECB and NBS exchange rate list as of 5 November 2024: 1 EUR = 25,343 CZK.

below. After 2050, it is recommended to use the constant value set for 2050 in subsequent years.

4. Results

There are fundamental differences in the variety of approaches to quantifying GHG emissions, countries apply different types of emissions in their CBA methodologies in terms of their structure, and there are differences in the values of emission factors and the monetization of the costs of GHG emissions.

4.1. Comparative Analysis of CBA Methodologies and Results

4.1.1. Comparison of the CBA Methodology in the Slovak Republic in the Field of Climate Change and Identification of Differences with Other Methodologies

The CBA methodology in the Slovak Republic is disproportionate toward GHG emissions, where indirect emissions from electricity production are considered for electric vehicles. It would, therefore, be appropriate to consider indirect emissions of pollutants from electricity generation in the methodology and in the external cost assessment.

For electric vehicles, the CBA methodology in the Slovak Republic considers indirect emissions (WtT) in grams per kWh of electricity consumption, and the EIB published three categories of emission factors by voltage. Table 40 in the CBA methodology in SR contains outdated values of emission factors for electricity consumption. Updating the values of the emission factors for electricity consumption is necessary.

The CBA methodology in the Slovak Republic considers CO₂, CH₄, and N₂O emissions; similarly, these types of GHG emissions are also applied in the methodology in the Czech Republic (emissions are directly listed in the methodology). This approach is correct.

The CBA methodology in the Slovak Republic does not consider indirect greenhouse gas (GHG) emissions (WtT) from the use of fossil fuels as an example of objectively reporting the impact of transport on GHG production for different modes of transport.

The source of emission factor values of selected fuels for indirect GHG emissions (WtT) or direct and indirect GHG emissions (well-to-wheel, WtW) can be, e.g.,

• ISO 14083 Greenhouse gases—Quantification and reporting of greenhouse gas emissions arising from transport chain operations, effective March 2023;
• Standard EN 16258;
• HBEFA Methodology 4.2.2.

The CBA methodology in the Slovak Republic applies the conversion of emissions of three types of greenhouse gas emissions (CO₂, CH₄, and N₂O) to a standard unit of CO₂es. Similarly, the methodologies in Hungary and the Czech Republic apply a similar conversion of emissions per unit CO₂es. This approach is correct. The CBA methodology in Austria only considers CO₂ emissions, does not consider CH₄ and N₂O emissions, and logically does not consider the conversion of emissions to CO₂es. This is related to the year of publication of the methodology, 2010.

Table 10. Comparison of the types of GHG emissions from road transport applied in the CBA [58,61,62,63].

Pollutant	SK	H	A	CZ
CO2	Yes	Not specified, the reference is generally to “greenhouse gas emissions”	Yes	Yes
CH4	Yes		No	Yes
N2O	Yes		No	Yes
Conversion to CO2e	Yes	Yes	No	Yes

Note: The methodology in the Czech Republic considers CH₄ and N₂O emissions, but the values of emission factors for CH₄ and N₂O are not given in the methodology.

provides a comparison of the applied GHG emissions of the different CBA methodologies and discusses the possibility of converting all pollutants to a common CO₂e unit.

4.1.2. Comparison and Evaluation of the Applied GHG Emission Factors in CBA Methodologies

GHG emission factors are expressed differently in the CBA methodologies. The CBA methodology in the Slovak Republic applies emission factors expressed in grams per 1 kg of fossil fuel consumed; the CBA methodology in Austria also applies a mass expression of emission factors related to the amount of fuel consumed (3.15 t CO₂/t fuel). The CBA methodology in Austria refers to the fuel consumed (t) and one CO₂ emission factor; it does not differentiate between different fuel types. For increased use of non-fossil fuel energy (e.g., hydropower for trolleybuses, trams, or railways), separate studies are needed. The methodology in Hungary applies emission factors in grams of CO₂es per vehicle-km. The methodology in the Czech Republic applies the expression of emission factors in grams per 1000 vehicle-km.

Two CBA methodologies provide GHG emission factors for specific fuels, the Slovak Republic and Hungary. The Slovak methodology applies GHG emission factors for diesel, petrol, and electricity. The Hungarian methodology uses GHG emission factors for diesel, petrol, CNG, and LPG.

Table 11. Comparison of selected parameters and characteristics of GHG emission factors from road transport in CBA methodologies.

	SK	H	A	CZ
Unit expression of the emission factor	g/kg of fuel	Not specified	3.15 t CO2/t fuel (type of fuel not specified)	g/1000 vehicle-km
Vehicle categorization	Passenger vehicles (petrol) Passenger vehicles (diesel) Light-goods vehicles (diesel) Medium-goods vehicles (diesel) Heavy-goods vehicles (diesel) Buses (diesel)	Bus Light commercial vehicle Trucks (3.5 t to 7.5 t) Trucks (7.5 t to 16 t) Trucks (16 t to 32 t) Trucks (more than 32 t) Moped Motorcycle	Vehicle category not specified	Passenger car, average Passenger car, city Long-distance bus Bus, city Light-goods vehicle Heavy-goods vehicle
Fuels proposed	Diesel Petrol Electricity	Diesel Petrol CNG LPG	Not specified	Not specified
Source data	[57,58,66]	[61,67]	[62]	[63]

compares selected parameters and characteristics of the GHG emission factors from road transport in the CBA methodologies.

For electric vehicles, the CBA methodology in the Slovak Republic considers indirect emissions (WtT) in grams per kWh of electricity consumption, based on the three categories of emission factors according to the voltage published by the European Investment Bank (EIB). In Hungary, for public transport using electricity, it considers indirect emissions (WtT) in grams per kWh of electricity consumption.

4.1.3. Comparison and Assessment of the Applied Unit Costs of Greenhouse Gases in CBA Methodologies

In terms of the unit cost of GHGs, the most up-to-date methodology in the Czech Republic considers carbon pricing from 2022 onwards, according to the EIB recommendations. Chapter 4 presents recommendations for updating the GHG unit cost values in the Czech Republic’s CBA methodology.

Table 12. Comparison of selected parameters and unit cost characteristics of GHG emissions from road transport in CBA methodologies.

	SK	H	A	CZ
Unit cost expression	EUR 86/ton eCO2	EUR 18.47/ton eCO2 (HUF 7560/ton eCO2)	EUR 50/t CO2	EUR 90/ton eCO2 until 2022
	Unit price t CO2es in EUR at the 2021 price level	European Investment Bank (2013) data, of which the median is recommended.	(2009 price level)	From 2022 onwards, for each year individually, according to Table 8.58 in the CBA (3594 CZK/ton in 2023)
Source data	[60,66]	[61] with reference to European Investment Bank (2013)	[62]	[63,65,68]

compares selected parameters and characteristics of the unit costs of GHG emissions from road transport in the CBA methodologies.

4.2. Case Study: Comparison of Differences in GHG Emissions and GHG Cost Calculations by Implementing the Principles of CBA Methodologies in Different Countries for a Model ofSemi-Trailer Transport on Road Infrastructure

The calculation and comparative analysis do not track the change in the number of km and the change in the amount of GHG caused by the use of “newly built infrastructure”, but the disparity in the calculation using the different CBA methodologies of the countries analyzed.

4.2.1. Calculation of GHG Emissions and Costs According to CBA Methodologies of Selected Countries and Comparison of Results

Inputs and input information for the calculation:

For the model calculation of GHG emissions for specific transport, a truck complying with the Euro 6 emission standard and a semi-trailer with the following technical data given as its gross weight, curb weight, technical axle load, technical coupling load, and permissible rear axle load are used.

Table 13. Truck specifications [the authors based them on the registration certificate of the truck unit].

Parameter	Value
Total trailer weight (legislative/constructional)	18,000 kg/20,500 kg
Curb weight	7230 kg
Technical axle loads	44,000 kg
Technical load of the coupling	7500 kg
Permissible rear axle load	11,500 kg/13,000 kg

and

Table 14. Semi-trailer specifications [the authors based them on the registration certificate of the semi-trailer].

Parameter	Value
Total trailer weight (legislative/constructional)	33,060 kg/39,000 kg
Curb weight	5490 kg
Technical axle loads	27,000 kg
Technical load of the coupling	12,000 kg
Loading area dimensions	13,620 × 2480 × 2700 mm

give the technical data of the truck and semi-trailer used.

Software allows you to define the input technical data of the selected vehicle. For the sample transport, the truck and semi-trailer data given in Table 13 and Table 14 were used.

The sample transport route, in which the GHG emissions, the emission costs, and the declaration are calculated, is shown in Figure 1. This route starts in Žilina and ends in Košice. The total length of the route is 295.25 km. The total diesel consumption is 109.39 L, and the average consumption per 100 km is 37.05 L. Input data are shown in

Table 15. Transport routing characteristics and calculations of energy consumption and greenhouse gas emissions—inputs for comparative analysis, processed by the authors using [69].

Characteristic	Value
Distance	295.25 km
Total diesel fuel consumption	109.39 L
Average diesel fuel consumption	37.05 L/100 km
According to HBEFA:
Amount of CO2 emissions	288.65 kg
Amount of N2O emissions	15.19 g
Amount of CH4 emissions	0.19 g
Amount of CO2e emissions
According to EN 16258:
Emissions WtT CO2es	56.47 kg
Emissions TtW CO2es	224.67 kg
Emissions WtW CO2es	281.14 kg

.

Table 16. Results of emission and fuel consumption calculations for the route implemented by the semi-trailer truck, processed by the authors using [69].

Route Length	Loading Status	CO2	CO2es	NOx	N2O	CH4	Fuel Consumption	L/100 km
295.29 km	25.5 t	288.65 kg	293.18 kg	80.39 g	15.19 g	0.19 g	109.39 L	37.05 L/100 km

,

Table 17. Results of the calculation of greenhouse gas emissions according to EN 16258 for the route implemented by the semitrailer, processed by the authors using [69].

Route Length	Loading Status	Energy—WTW	Emissions—WTW	Energy—TTW	Emissions—TTW	Energy—WTT	Emissions—WTT
295.29 km	25.5 t	3896.4 MJ	281.14 kg CO2e	3166.1 MJ	224.67 kg CO2e	730.3 MJ	56.47 kg CO2e

and

Table 18. Emission factors used, processed by the authors using [69].

Conversion Factor	Well to Wheel	Tank to Wheel	Well to Tank
Kg CO2 per liter diesel	3.24	2.67	0.57
MJ per liter diesel	42.7	35.9	6.8
Kg CO2e per liter diesel (biofuel)	1.92	0	1.92
MJ per liter diesel (biofuel)	68.5	32.8	35.7
Kg CO2e per liter diesel; incl. 7% (volume percent) biofuel component	3.17	2.54	0.64
MJ per liter diesel; incl. 7% (volume percent) biofuel component	43.99	35.74	8.24

show the results of the emission calculations according to the HBEFA methodology and according to EN 16 258 for the considered transport route from Žilina to Košice and the semi-trailer truck combination used.

The following conversion factors were used:

4.2.2. Calculations of GHG Emissions and Costs According to the CBA Methodology in the Slovak Republic

The amount of greenhouse gas emissions

Calculation of the amount of CO₂ emissions in the Slovak Republic produced in transport according to the CBA was calculated using Equation (S3):

$${AGHG RT}_{ik}={AVFC}_i\ast {DTV}_j\ast {DF}_i\ast {EF GHG}_{ik}=0.3705\ast 295.25\ast 0.82\ast 3140$$

$${AGHG RT}_{ik}=281657.694 g {CO}_2=281.658 kg {CO}_2$$

The amount of CH₄ emissions in the Slovak Republic produced during transport according to the CBA was calculated by Equation (S3):

$${AGHG RT}_{ik}={AVFC}_i\ast {DTV}_j\ast {DF}_i\ast {EF GHG}_{ik}=0.3705\ast 295.25\ast 0.82\ast 0.27$$

$${AGHG RT}_{ik}=24.21897 g {CH}_4=0.0242 kg {CH}_4$$

The amount of N₂O emissions in the Slovak Republic produced during transport according to the CBA was calculated by Equation (S3):

$${AGHG RT}_{ik}={AVFC}_i\ast {DTV}_j\ast {DF}_i\ast {EF GHG}_{ik}=0.3705\ast 295.25\ast 0.82\ast 0.051$$

$${AGHG RT}_{ik}=4.574695 g N_2\mathrm{O}=0.00458 kg N_{2}O$$

The amount of eCO₂ emissions by CBA in the Slovak Republic produced during transport was calculated according to Equation (S3):

$${A e{CO}_2 RT}_i={CO}_2\ast 1+{CH}_4\ast 25+N_2\mathrm{O}\ast 298$$

$${A e{CO}_2 RT}_i=281.65\ast 1+0.0242\ast 25+0.00458\ast 298=283.6198 kg e{CO}_2$$

The cost of greenhouse gas emissions was calculated by applying Equation (S4):

$${Ce{CO}_{2}RT}_i={Ae{CO}_{2}RT}_i\ast UC{e{CO}_{2}RT}_i=0.2836198te{CO}_2\ast 193.3{\displaystyle \frac{eur}{1}}tone{CO}_2=54.824eur$$

According to the CBA methodology, the cost of greenhouse gas emissions for the model transport in the Slovak Republic is EUR 54.284.

4.2.3. Calculation of GHG Emissions and Costs According to the CBA Methodology in Hungary

Equation (S7) and the value of the emission factor from Table 6 were used to calculate CO₂e emissions according to the CBA methodology in Hungary. Given the semi-trailer truck’s total weight, we chose the category “Trucks > 32 t” and the fuel diesel. For diesel and the category “Trucks > 32 t”, the emission factor for CO₂es is 906 g CO₂es/1 km traveled by the semitrailer unit.

The amount of CBA CO₂e emissions in Hungary produced during transport was calculated according to Equation (S7):

$${A CO}_{2}e RT={EF CO}_2 e Vi\ast {DTV}_j=0.906 kg{\displaystyle \frac{{CO}_{2}e}{1}} km\ast 295.25 km$$

$${A CO}_{2}e RT=267.4965 kg {CO}_2$$

The cost of CO₂e greenhouse gas emissions produced by transportation in Hungary according to CBA was calculated using Equation (S6):

$$The cost of greenhouse gas emissions={A CO}_{2}e RT\ast P_{GHG}=0.2674965 t e{CO}_2\ast 9198.501{\displaystyle \frac{HUF}{1 t e{CO}_2}}=2460.567 HUF=6.012 EUR$$

Note: The price of 1 t CO₂es is based on the CBA methodology in Hungary; it was set for 2024 based on the GDP growth rate in Hungary according to the CBA methodology.

4.2.4. Calculation of Greenhouse Gas Emissions and Costs According to the CBA Methodology in Austria

The amount of CBA CO₂ emissions in Austria produced during transport was calculated according to the following equation:

$${A CO}_{2}RT=A GHG M\ast {EF CO}_2=AFC V\ast DF\ast {EF CO}_2$$

$${A CO}_{2}RT=109.39 litres\ast 0.832{\displaystyle \frac{kg}{l}}\ast 3.15 kg{\displaystyle \frac{{CO}_2}{1}}kg diesel fuel$$

$${A CO}_{2}RT=286.688 kg {CO}_2$$

Note: we consider the DF of diesel fuel according to the HBEFA for Austria as 0.832 kg/L.

The greenhouse gas cost (climate protection cost) of road transport was calculated using Equation (S8):

$${CCO}_{2}RT={ACO}_{2}RT\ast {UCCO}_{2}RT=0.286688tCO2\ast 50{\displaystyle \frac{eur}{1}}ton{CO}_2=14.334eur$$

4.2.5. Calculation of Greenhouse Gas Emissions and Costs According to the CBA Methodology in the Czech Republic

For the calculation of CO₂e emissions according to the CBA methodology in the Czech Republic, the CO₂ emission factor for heavy-goods vehicles given in Table 8 was used, and it reached a value of 604 g CO₂/1 vehicle-km.

For the semi-trailer combination used, due to its total weight, we chose the category “Heavy GV” and diesel fuel.

The amount of CBA CO₂ emissions in the Czech Republic produced during transport was calculated as follows:

$${ACO}_{2}RT={EF CO}_{2}Vi\ast {DTV}_{jkv}=0.604 kg{\displaystyle \frac{{CO}_2}{1}}km\ast 295.25 km$$

$${ACO}_{2}RT=178.331 kg {CO}_2$$

$${Ae{CO}_{2}RT}_i=178.331 kg\ast 1+0.00019 kg\ast 25+0.0159 kg\ast 298=283.6198 kg e{CO}_2$$

$${Ae{CO}_{2}RT}_i=178.331 kg\ast 1+0.005 kg+4.527 kg=182.863 kg e{CO}_2$$

The cost of CO₂ greenhouse gas emissions produced during transport according to the CBA in the Czech Republic was calculated as the GHG cost of road transport using Equation (S9):

$$CGHG RT=AGHG RT\ast UCGHG RT$$

$$The cost of greenhouse gas emissions={AeCO}_{2}RT\ast P_{GHG=}0.182863 t e{CO}_2\ast 4061{\displaystyle \frac{CZK}{1te{CO}_2}}=742.607 CZK=29.302 EUR$$

Naturally, this study aims to highlight the differences in the ways GHG emissions and climate change costs are calculated and the parameters applied, including emission factors and unit costs of climate change, in the national CBA manuals. These may ultimately influence the results of the GHG analysis when considering specific transport projects in individual countries. The last row of

Table 19. Results of a comparative study of the GHG emissions and GHG costs of semi-trailer truck transport.

Parameter	CBA Methodology
	CBA SK	CBA HU	CBA AT	CBA CZ
CO2 (kg)	281.658	-	286.688	178.331
CH4 (kg)	0.0242	-	-	0.00019 1
N2O (kg)	0.00458	-	-	0.01519 1
CO2e (kg)	283.6198	267.4965	-	182.863
GHG costs (EUR)	EUR 54.824	EUR 6.012 (HUF 2460.567)	EUR 14.334	EUR 29.302 (CZK 742.607)
GHG costs (%, SK = 100%)	100%	10.97%	26.15%	53.45%

¹ Considers only CO₂ due to the unavailability of data on emission factors for CH₄ and N₂O emissions in the CBA methodology in the Czech Republic; data from the calculation of CH₄ and N₂O emissions in [53,69] were used. Note 1—conversion to EUR currency according to the ECB and NBS exchange rate list as of 5 November 2024: 1 EUR = 25.343 CZK; 1 EUR = 409.25 HUF. Note 2—EN after adjustment considering a diesel density of 0.832 kg/L.

provides a percentage comparison of the climate change costs of the model transport using national CBA methodologies. The calculated climate change costs are more than nine times the costs calculated according to the methodology in Hungary, almost four times the costs calculated according to the methodology in Austria, and almost twice the costs calculated according to the methodology in the Czech Republic.

5. Discussion and Proposed Recommendations for Parameters and Their Adjustment in the CBA Methodology in the Slovak Republic

Regarding the source data on unit costs of pollutants, the CBA methodology in Slovakia is the most up to date of the methodologies compared, based on EUROPEAN COMMISSION: Handbook on External Cost of Transport, January 2019.

Table 20. Length of superior infrastructure per square kilometer of territory in the compared countries, the authors based on [70].

Year/Country	SK	H	A	CZ
2020	0.0167	0.0191	0.0209	0.0165
2021	0.0173	0.0200	0.0209	0.0171
2022	0.0176	0.0201	0.0209	0.0173
2023	0.0176	0.0201	0.0209	0.0176

compares the density of the superior infrastructure in kilometers per square kilometer of territory, with the Slovak Republic performing below the standard despite moderate growth in recent years. This lower share is also due to the still unfinished infrastructure along the routes of the European transport corridors. This is also one of the reasons why a country comparison analysis has been carried out and shows its importance.

5.1. Recommendation 1: Proposal to Change the Values of the Fuel Density Used in the Methodological Manual of the CBA in the Slovak Republic, Section 5.2.2.6 (New Manual 4.2.2.6)

The density values used in the CBA methodology in the Slovak Republic are low and underestimate the results achieved in the area of climate change costing. Therefore, we analyzed the density values of selected fuels from relevant sources, e.g., HBEFA methodology, EN 16258 and ISO 14083 standards, or information from fuel producers (e.g., Slovnaft a. s.) or from other relevant projects and studies (e.g., Join Research Centre, JEC Well-To-Wheels report v5 [71]).

Figure 2 compares the density of petrol and diesel under the CBA methodology applicable in the Slovak Republic, the HBEFA methodology, and two standards—ISO 14083 and EN 16258.

Table 21. Comparison of the density of selected fuels according to the HBEFA methodology [53].

ID		Unit	A	FR	DE	N	SE	CH	Average Value	Median Value
1	petrol	kg/L	0.742	0.745	0.742	0.742	0.742	0.737	0.742	0.742
9	petrol 2S	kg/L	0.742	0.745	0.742	0.742	0.742	0.737	0.742	0.742
2	diesel	kg/L	0.832	0.855	0.832	0.832	0.832	0.83	0.836	0.832
31	biodiesel	kg/L	0.883	0.883	0.881	0.881	0.881	0.86	0.878	0.881
30	vegetable oil	kg/L	0.92	0.92	0.92	0.92	0.92	0.92	0.920	0.920
21	ethanol (bio)	kg/L	0.794	0.794	0.7894	0.7894	0.7894	0.794	0.792	0.792
23	E85	kg/L	0.7862	0.788	0.78229	0.78229	0.78229	0.78545	0.784	0.784
3	CNG	kg/Nm3	0.716	0.69	0.716	0.716	0.716	0.795	0.725	0.716
51	biogas	kg/Nm3	0.716	0.69	0.716	0.716	0.716	0.795	0.725	0.716
6	LPG	kg/L	0.54	0.538	0.6	0.6	0.6	0.54	0.570	0.570
53	LNG	kg/Nm3	0.716	0.452	0.716	0.716	0.716	0.716	0.672	0.716
52	propane	kg/Nm3	0.716	0.538	0.716	0.716	0.716	0.716	0.686	0.716
5	electricity	not specified	0	0	0	0	0	0	0.000	0.000
8	hydrogen	not specified	0	0	0	0	0	0	0.000	0.000
4	petroleum	kg/L	0.8	0.8	0.8	0.8	0.8	0.799	0.800	0.800

compares the density of selected fuels by country under the HBEFA methodology, version 4.2.2, and includes the calculated mean and median values of the fuels. The names of fuels and energy sources are given in their original wording as used in the HBEFA methodology. The ID represents the code applied to the fuel or energy source within the HBEFA methodology.

Density values in the CBA methodology in the SR are lower compared to those in the HBEFA methodology. For gasoline, the density value in the CBA methodology in the SR is lower by 2.92%; for diesel, it is lower by 1.86%; and for CNG, it is lower by 3.45%. The difference in density values for petrol between the CBA SR methodology and the ISO 14083 and 16258 standards is even more pronounced, with the SR CBA value being 3.10% lower than the ISO 14083 standard and 3.36% lower than the EN 16258 standard. For diesel, the difference is the same as the HBEFA methodology; for CNG, ISO 14083 and EN 16258 do not provide a density value.

The tables below compare the density values of the selected fuels under the different methodologies and standards against the values in the CBA methodology in the Slovak Republic.

Table 22. The proportion of fuel density used in the CBA in the Slovak Republic relative to the fuel density from other sources (%), the authors’ elaboration based on [53,55,56,58,64].

	CBA—SR Against HBEFA (Average)	CBA—SR Against HBEFA (Median)	CBA—SR Against ISO 14083	CBA—SR Against EN 16258
Petrol	97.08	97.04	96.90	96.64
Diesel	98.14	98.56	98.56	98.56
CNG	96.55	97.77	Standard N/A	Standard N/A

contains the share of CBA SR fuel density in % of the fuel density value from other sources.

Table 23. Difference in the fuel density used in the CBA in SR compared to the fuel density from other sources (%), authors’ elaboration based on [53,55,56,58,66].

	CBA—SR Against HBEFA (Average)	CBA—SR Against HBEFA (Median)	CBA—SR Against ISO 14083	CBA—SR Against EN 16258
Petrol	−2.92	−2.96	−3.10	−3.36
Diesel	−1.86	−1.44	−1.44	−1.44
CNG	−3.45	−2.23	Standard N/A	Standard N/A

contains the difference in the CBA SR fuel density to the fuel density value (%) from other sources.

The fuel density value influences the amount of pollutants and greenhouse gases released by road transport and, thus, the associated external costs.

Other sources of information on the density value of selected fuels may be

• Slovnaft Refinery as the largest supplier of fuel in the Slovak Republic;

  ○

  Petrol: range 0.720–0.775 kg/L [72];

  ○

  Diesel: range 0.82–0.845 kg/L [72];

• Join Research Centre, JEC Well-To-Wheels report v5, ISBN 978-92-76-20109-0, doi:10.2760/100379, European Union, 2020, Table 8 and Table 9 of document [71].

Table 24. Density values of selected fuels [53,55].

	Current Density Value	New Density Value	Unit
Petrol	0.72	0.743	kg/L
Diesel	0.82	0.832	kg/L
Natural gas	0.70	0.725	kg/m3

Note: petrol, diesel—ISO 14083, natural gas—average of HBEFA values (ISO 14083 does not specify CNG density value).

proposes recommended density values for selected fuels to adjust the CBA methodology in the Slovak Republic. The table also contains density values according to the current CBA methodology in the Slovak Republic.

5.2. Recommendation 2: Adjustment of Road Vehicle Categories for Pollutant Emissions and Related External Costs in the Methodological Manual of the CBA in the Slovak Republic

The categorization of road vehicles and the emission factors (g/kg) of road vehicles are defined in Table 42 of the CBA Methodology Manual, version 1.0. The CBA methodology in the Slovak Republic states: “Normally, standardized emission factors are established taking into account the typical vehicle fleet of a given country or region, for different vehicle categories. For the purpose of this guide, the European Environment Agency (EEA) data for 2019 can be used in terms of the following table, meaning Table 42 of the methodology, is presented in Chapter 4.2.2.6.

We recommend adjusting the categories of road vehicles for pollutant emissions and associated external costs. The application of a clear categorization of road vehicles, including a separate category for ‘buses’ (not merging several vehicle categories into groups).

A comparison of the vehicle categories used by each country in the CBA methodologies for pollutant and GHG emissions and associated costs shows that the Czech Republic uses the same vehicle categorization for both pollutant and GHG emissions. This is not the case in the CBA methodology in the Slovak Republic. It is not clear from Table 42 of the Slovak methodology whether the category “Other trucks and buses (diesel)” includes the category of medium-weight trucks and the category of heavy-duty trucks used in Table 45 for GHG emissions.

We recommend using in Table 42 of the methodology the same categorization used in Table 45, Emission Factors (g/kg) of Road Vehicles (Conventional Fuels) of the CBA Methodology Manual, version 1.0, as follows:

• Passenger vehicles (petrol);
• Passenger vehicles (diesel);
• Light trucks (diesel);
• Medium-duty trucks (diesel);
• Heavy-goods vehicles (diesel);
• Buses (diesel).

Both Table 42 and Table 45 of the CBA Methodology Manual, version 1.0, are based on the same source (EMEP/EEA Air Pollutant Emission Inventory Guidebook 2019 (1.A.3.b. Road transport)).

5.3. Recommendation 3: Suggested Change to the GHG Emission Factor Parameter for Road Vehicles (g/kg) in the CBA Methodology Manual (Table 45 of the CBA Manual)

The proposal is based on the possibility of including indirect GHG emissions from fuel production (WtT + TtW). This is also an objectified approach because WtT emissions are applicable to electric vehicles. ISO 14083 can be used as a source of emission factor values visible in

Table 25. Greenhouse gas emission factor values for selected vehicle categories [55] considering WtT + TtW.

Vehicle Category	Current Values in the CBA Methodology Used in the Slovak Republic			Values According to ISO14083
	CO2	CH4	N2O	CO2e
Passenger cars (petrol)	3180	1.09	0.206	3830
Passenger cars (diesel)	3140	0.23	0.087	3740
Light commercial vehicles (diesel)	3140	0.16	0.056	3740
Medium-duty vehicles (diesel)	3140	0.27	0.051	3740
Heavy-goods vehicles (diesel)	3140	0.27	0.051	3740
Buses (diesel)	3140	0.27	0.051	3740

.

5.4. Recommendation 4: Retain Conversion Factors for Converting Individual GHG Emissions to a Standard Unit of CO₂es

The CBA methodology in the Slovak Republic applies the conversion of emissions of three types of greenhouse gas emissions (CO₂, CH₄, and N₂O) to a common unit of CO₂es. Similarly, the methodologies in Hungary and the Czech Republic apply a similar conversion of emissions per unit CO₂es. This approach is correct. The conversion factors for the calculation of CO₂es are given in

Table 26. Conversion factors for calculating CO₂es (t).

	CO2	CH4	N2O
CO2es	1	25	298

.

If the current approach to calculating GHG emissions and associated climate change costs in the form of direct emissions (TtW) from fossil fuel use only is retained (the recommendation to include indirect emissions from fuel production (WtT) will not be considered), then we propose to retain the currently applied conversion of GHG emissions to CO₂es. This is a more comprehensive approach to the issue and the declaration of GHG emissions compared to the situation if only the CO₂ impact is declared as is the case, e.g., in the CBA methodology in Austria.

5.5. Recommendation 5: Implementation of Indirect GHG Emissions Related to Road Transport Fuel Consumption in the CBA Methodology Manual

In actual practice, transport, freight forwarding, and logistics organizations in European countries, including the Slovak Republic, declare the environmental impact of their activities by issuing declarations on energy consumption and greenhouse gas emissions. Declarations for specific transport by road freight vehicles can be issued, for example, using the PTV software Map & Guide. The EcoTransIT multimodal calculator can also be used to calculate and issue the declaration.

Also, in the conditions of the Slovak Republic, the ISO standard is implemented in the Slovak standardization system STN EN ISO 14025 Environmental labels and declarations, Type III environmental declarations, Principles and procedures. Type III represents quantified environmental information covering the entire life cycle of a product intended for comparison of products with the same functional characteristics and independently verified by a third party—Environmental Product Declaration (EPD). The general objective of the EPD is to use verifiable and accurate information to support the demand for and supply of products that have a lower negative impact on the environment. It acts as evidence for and/or a claim of a sustainable product that can be used by companies for commercial purposes. EPDs are often required in green public procurement (GPP), tendering by private companies, and environmental management systems.

Indirect emissions (WtT) of greenhouse gases, expressed in CO₂es, represent a significant proportion of the total emissions from road transport vehicle operations. Indirect emissions amount to 15.8% for petrol, 17.69% for diesel, 12.7% for CNG, and 10.4% for LPG of the total GHG emissions according to EN 16258. Indirect emissions amount to 16.71% for petrol, 15.24% for diesel, 22.07% for CNG, and 17.79% for LPG of the total GHG emissions according to ISO 14083. The values are shown in

Table 27. CO₂e pollutant emissions and their structure by WtT, TtW, and WtW for selected pollutants using EN 16258 and ISO 14083.

Standard	Unit	WtT	TtW	WtW (WtT + TtW)
Petrol
EN 16258	kg CO2es/kg	0.61	3.25	3.86
	%	15.80	84.20	100
ISO 14083	kg CO2es/kg	0.64	3.19	3.83
	%	16.71	83.29	100
Diesel
EN 16258	kg CO2es/kg	0.69	3.21	3.9
	%	17.69	82.31	100
ISO 14083	kg CO2es/kg	0.57	3.17	3.74
	%	15.24	84.76	100
CNG
EN 16258	kg CO2es/kg	0.39	2.68	3.07
	%	12.70	87.30	100
ISO 14083	kg CO2es/kg	0.79	2.79	3.58
	%	22.07	77.93	100
LPG
EN 16258	kg CO2es/kg	0.36	3.1	3.46
	%	10.40	89.60	100
ISO 14083	kg CO2es/kg	0.66	3.05	3.71
	%	17.79	82.21	100

.

If indirect GHG emissions from fuel consumption were also considered in the CBA methodology (similar to electricity), the change in total GHG emissions and the value of the associated external costs would be higher by the above indirect emissions percentages (%).

5.6. Recommendation 6: Regular Updates of the CBA Methodology to Reflect Changes in EU Legislation and Changes in ISO and EN Standards Related to Pollutant Emissions, Greenhouse Gas Emissions, and Their Economic Valuation, and the Application of Additional Vehicle and Fuel Categories

In the future, we recommend considering changing the structure of the in-service vehicles by additional categories regarding the type of fuel used and implementing emission factors for additional fuels into the methodology. Sources of information on parameter values can be ISO 14083, EN 16258, and the HBEFA methodology.

When extending the categories of road vehicles, we recommend using the same categorization for pollutant emissions, GHG emissions, and associated external costs.

Such an extension of vehicle categories is also possible regarding vehicle categories and fuel and energy sources, respectively, as listed in Chapters 4 and 5 of the European Commission’s Handbook on External Cost of Transport, January 2019, on which the current CBA Methodological Guide, version 1.0, is based.

6. Conclusions

The differences in the application of CBA methodologies in the examined countries are significant. The amount of CO₂ emissions calculated by applying the CBA methodology in the Slovak Republic is 1.8% lower compared to the CBA methodology in Austria and 57.9% higher compared to the CBA methodology in the Czech Republic. When the GHG emissions are expressed in terms of CO₂es, the amount in Slovakia is 6.03% higher than in the Hungarian methodology and 55.1% higher than in the Czech methodology.

The differences are even more pronounced in terms of GHG costs. The climate change costs are 9.11 times higher in the CBA methodology in Slovakia than in Hungary, 3.825 times higher than in the Austrian methodology, and 1.871 times higher than in the Czech methodology for the model of road freight transport. These differences are related to the disparities that have already been analyzed and identified in the CBA methodologies.

For GHG emissions and the calculation of the change in GHG emissions, the current CBA methodology in the Slovak Republic also considers indirect emissions for electricity (WtT approach) but does not consider indirect emissions for other fuels. The same approach should also be applied to other fuels, where currently only direct GHG emissions based on fuel consumption by road transport vehicles during their operation are considered (TtW approach).

Indirect (WtT) GHG emissions expressed in eCO₂ represent a significant proportion of the total emissions produced from the operation of road transport vehicles, and their inclusion in the total GHG emissions represents an objectified approach that has been applied in transport practice for more than 10 years. For example, the declaration of energy consumption and GHG emissions according to EN 16258 at the company level for the operation of specific vehicles, the transport of specific groups of goods by road freight transport, and the transport of passengers by passenger transport on specific transport routes has been used by transport, freight forwarding and logistics organizations in European countries, including the Slovak Republic, for several years.

If indirect GHG emissions from fuel consumption were also considered in the CBA methodology (similar to electricity), the change in total GHG emissions and the value of the associated external costs would be higher. WtT GHG emissions are 15.8% for petrol, 17.69% for diesel, 12.7% for CNG, and 10.4% for LPG of the total GHG emissions according to EN 16258. A new ISO 14083 standard is also in effect from March 2023. WtT GHG emissions are 16.71% for petrol, 15.24% for diesel, 22.07% for CNG, and 17.79% for LPG of the total GHG emissions according to ISO 14083.

The CBA methodology should be regularly updated to respond to changes in EU legislation, to changes in ISO and EN standards, as well as to the requirements of newly adopted ISO and EN standards related to pollutant emissions, GHG emissions, emission factors and their economic evaluation.

In the future, the implementation of indirect emissions of other pollutants and their associated costs in the CBA methodology will also need to be considered; real transport practice at the company level already applies the declaration of indirect pollutant emissions in addition to GHG emissions (e.g., the EcoTransIT emission and energy calculator).

In the future, the methodology updates should also respond to the changes in the structure of sales and operation of vehicles by additional types with respect to the type of fuel used, and emission factors for additional fuels should also be implemented in the methodology. Sources of information on parameter values are given in the relevant chapters of this study.

The categories of road vehicles should be standardized when considering the changes in the amounts of individual pollutants and greenhouse gases. In the case of extending the categories of road vehicles, using the same categorization for both pollutant emissions and GHG emissions and associated external costs is recommended. Vehicle categories and fuels or energy sources should be in line with Chapters 4 and 5 of the European Commission’s Handbook on External Cost of Transport, January 2019.

This case study on model transport and the applied procedures for calculating GHG emissions and costs confirmed significant differences in calculation methods, values of emission factors, and GHG unit costs between countries. These are confirmed by the varying calculation ratios per country, with not all countries under comparison applying all types of GHG emissions or conversion per unit of CO₂ equivalents.

The new standard ISO 14083:2023 Greenhouse gases—Quantification and reporting of greenhouse gas emissions arising from transport chain operations is highly topical and its possible implementation in GHG emission calculations will be the subject of further research. Significant differences in approaches to calculating GHG emissions and climate change costs have already been identified when comparing the four national CBA manuals. What differences would be identified if comparing approaches in the 16 countries (according to Vademecum) that have national CBA manuals for transport project appraisal? The issue of GHG emissions and climate change costs is part of the CBA methodology, and further research will also focus on areas such as the economic valuation of passenger time savings, valuation of freight transport time, fuel consumption and vehicle operating costs, the production of other pollutants by vehicles in addition to GHG emissions, and the adequacy and timeliness of the practices applied in each area.

A limiting factor for the comparison of CBA methodologies and their application in the GHG area is the lack of input data in the form of detailed vehicle structures and intensities, as well as their operational characteristics (vehicle category, fuel type, fuel consumption, and emission limit). Therefore, for this case study, a route planner and an emission calculator were applied using a specific semi-trailer with known technological–technical parameters. A limiting factor for the combination of methodologies is also the different years of publication of the CBA methodologies in specific countries, or the different years of their updates. Thus, the methodologies reflect different levels of updating and compliance with the currently applicable regulations and technical and technological development.