Advancing Sustainable Interoperability Between Standard and Broad-Gauge Railway Systems

Abstract

The focus of this paper is the development of a sustainable model for increasing the interoperability between 1435 mm (standard gauge) and 1520 mm (broad gauge) railway systems and fostering the development of efficient and sustainable railway networks. By merging technical, economic and environmental variables, the model aids strategic planning and enhances connectivity and efficiency of multimodal transportation. The proposed model considers important criteria, from diverse perspectives, that encompass interoperability and sustainable development of these railway systems. The significance of these criteria was evaluated using an expert survey, calculating the weights according to the Analytic Hierarchy Process (AHP) and then validating them applying the PROMETHEE method. By ranking the criteria based on their significance, the model helps identify development alternatives and corresponding technological solutions for interoperable railway systems. This model establishes the basis for a methodology that secures the sustainable development of railway networks according to their technical, operational, and strategies objectives.

1. Introduction

One of the major strategic objectives of Lithuania is the implementation of the Rail Baltica Project aiming to integrate the Baltic States in the European rail network. This ambitious project pulls in five EU nations: Poland, Lithuania, Latvia, Estonia, and, in a way, Finland too. The Rail Baltica Project stands out as the most significant railroad infrastructure initiative in the Baltic region over the past century [1,2,3]. It is not just about trains and infrastructure, but it is set to create a fresh economic corridor that will link Northeast Europe more closely with the wider European Union.

The objective of this initiative is to construct a 390 km high-speed railway infrastructure in Lithuania based on 1435 mm gauge standard. It also includes the development of international railway stations in Kaunas, Vilnius, Panevėžys, and more than seven regional stations for passenger and goods transport, as well as connecting stations to European destinations [4,5]. At the same time, perspective issues are being considered for the existing 1520 mm gauge railway network’s sustainable integration. For example, if the 1435 mm standard gauge is designated as a primary railway network, it should be decided how much of the current 1520 mm gauge infrastructure should be converted to standard gauge.

The transformation of Lithuania’s railway system from a mostly 1520 mm broad gauge network to the European 1435 mm standard gauge represents more than a domestic infrastructure upgrade. This situation represents a worldwide problem for many nations with diverse railway gauges that require effective methods for integration and transition. Multi-gauge railway systems present operational difficulties throughout Eastern Europe, the Baltics, Central Asia, South America, and parts of Africa. The railway systems of Finland, Ukraine, Kazakhstan, India, Brazil, and Argentina use mixed gauges, which poses challenges to cross-border transport and freight logistics while affecting interoperability [6,7,8].

One of the major sustainability hurdles for numerous countries across Europe, Asia, South America, and Africa is the inconsistency in railway gauges [9,10,11,12,13]. When countries have mixed-gauge rail systems, they encounter interoperability issues that can result in inefficiencies in freight logistics, delays for passengers, and higher operational costs.

The challenge is clear across various global regions. In Eastern Europe and the Baltics, the differing track gauges—1435 mm versus 1520 mm—make it tough to achieve smooth connectivity between the EU and post-Soviet railway systems. Moving to Central Asia, countries like Kazakhstan stick to the 1520 mm gauge, which limits their ability to integrate seamlessly with China.

Solving the interoperability problem is not just a technical challenge; it affects economic growth, trade efficiency, and regional integration. In Lithuania, the transformation of its railway system—shifting from the 1520 mm broad gauge (inherited from the Soviet era) to the 1435 mm European standard gauge—is a strategic priority. The Rail Baltica Project is the most significant railway infrastructure initiative in the region, aiming to fully integrate the Baltic States into the EU rail network. However, the numerous major challenges that Lithuania faces include the following:

A.

Gauge transition and integration: How much of the existing 1520 mm network should be converted to 1435 mm?

B.

Economic impact: A lack of interoperability raises transportation costs, affecting trade efficiency and logistics.

C.

Multimodal connectivity: Lithuania’s railway transformation must consider freight hubs, passenger stations, and logistics centers to ensure smooth transport across different gauge systems.

D.

Sustainability and infrastructure planning: The transition must align with environmental, economic, and operational sustainability goals.

In both national and international contexts, solving railway gauge disparity is essential for improving transport efficiency, reducing logistical costs, and fostering economic integration. The development of an expert model aims to enhance railway interoperability by addressing key technical, economic, and environmental factors, particularly focusing on the gauge transition from 1520 mm to 1435 mm. The objectives of developing this model are as follows:

-

Define interoperability criteria: establish key technical, operational, and economic factors affecting railway integration;

-

Assess the relative importance and impact of the defined criteria on interoperability: construct an AHP-based model to prioritize and weigh the significance of each criterion in improving railway integration;

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Identify primary challenges related to track and system integration: analyze the technical and operational obstacles that may hinder smooth interoperability and system integration.

2. Materials and Methods

Fostering sustainable interoperability between 1520 mm and 1435 mm gauge railway systems aligns with global sustainable development trends such as reducing carbon dioxide emissions and efforts contributing to long-term economic growth, taking into account economic security and accessibility. Social inclusion and mobility are important aspects of sustainability, which are encouraged by improving transport accessibility and connectivity. Technological innovations, such as electrification and automation, are essential for achieving sustainability goals and reducing the physical impacts of climate change. Finally, efficient resource use and infrastructure optimization align with global trends aimed at creating a sustainable and efficient transport system.

Before conducting the expert survey, a list of criteria was developed. This list was based on both a review of relevant literature and expert judgment. A group of 10 individuals, assembled by the authors, identified 7 key criteria groups (see Table 1). These criteria groups were selected drawing on insights from the literature and were later subject to expert evaluation, during which specific weights would be assigned to each. The selection process followed the approach outlined by Yazdani et al. [14].

Table 1. Sustainability-oriented criteria groups for strategic planning of interoperable standard and broad-gauge railway systems.

Criteria Group	Brief Description of the Criteria Group	References
Q1 Economic and Market conditions	The criteria in this group correspond to the objectives of reducing transport costs and improving the movement of goods and passengers, thereby increasing Lithuania’s competitiveness in the international market and promoting business development and attracting investment. The criteria in the Economic and market conditions group describe the adequacy of the services provided to passengers, consignors, and consignees of goods transported by rail and the economic conditions under which passenger and freight transport undertakings providing rail services operate. The economic conditions for rail passenger and freight operators are expressed in terms of the capacity of the public infrastructure, which has a direct impact on the conditions for access to the market and the opportunities for operating on it. The infrastructure capacity determines the lifetime of rolling stock and the corresponding number of rolling stock. The higher the infrastructure capacity, the lower the time required to transport passengers and freight and the correspondingly smaller the fleet size. The size of the rolling stock also determines the efficiency of rolling stock operation and the number of depots for maintenance, inspection, and repair work.	[2,15,16,17]
Q2 Social Benefits	The criteria of the social benefit group are aimed at improving the comfort of rail transport for all passengers, including people with disabilities, creating new jobs and stimulating regional economic development. The social benefit criteria describe the adaptability of rail infrastructure to the needs of passengers with reduced mobility. They also describe the attractiveness of pricing for passengers belonging to social groups, the number of jobs created by the construction and operation of the railway infrastructure, the upgrading of local businesses, and the level of satisfaction of the general public and local businesses with the procedures for the acquisition of land for public needs, which not only involve the acquisition of agricultural land but also residential, public, industrial, and commercial land and buildings.	[1,15,17,18,19]
Q3 Infrastructure Development	The criteria of the Infrastructure Development Group focus on the proper development of a modernized railway system that will connect cities and industrial centers, reduce road congestion, and increase transport efficiency. The infrastructure development criteria describe the importance of the development of new railway infrastructure and the reconstruction of existing intersecting infrastructure (railway tracks of different gauges, motorways, electricity transmission and distribution networks, gas pipelines, etc.). Infrastructure development must be carried out in a sustainable, i.e., environmentally friendly, manner, which is determined by the engineering topography and geological and geotechnical conditions of the area. Therefore, in addition to crossing rivers and their valleys, water channels, rail and road routes, and even animal migration corridors, it is necessary to construct two-level animal crossings (thresholds and green bridges) and to install noise and vibration reduction measures near public and residential areas.	[6,20,21,22]
Q4 Technological Progress	The introduction of advanced technologies will make rail transport faster, safer, and more efficient, contributing to fostering innovation in Lithuania and the Baltic States. The criteria of the Technological Progress Group include technical parameters, performance parameters, and quantitative parameters for the main railway subsystems (infrastructure, energy supply, traffic management, and control and signaling subsystems). The main parameters of these subsystems, expressed in terms of criteria, are the technical parameters of the railway (design speed, maximum loads, geometrical parameters, power supply system, traffic management, and control and signaling systems) and the quantitative parameters of the railway (length of tracks at stations, length of tracks at intermediate stages, and total length of structures on the line).	[4,23,24,25]
Q5 Sustainability and Ecology	The development of rail systems balances transportation modes by shifting automobile transport and short-distance (up to 500 km) air transport passenger to rail transport. This transportation mode balancing significantly reduces air pollution and noise, conserves natural resources, and contributes to reducing climate change by promoting environmentally friendly transport. The reduction in air pollution is particularly evident in residential areas located along the motorways. The criteria in the Sustainability and Ecology cluster also cover the negative impacts of the rail systems to be developed on public health (noise, vibration, and electromagnetic radiation), as well as on environment (deforestation, landscape, natural framework, ground and surface water, protected areas and sites, Natura 2000 territories, and wildlife) and on cultural heritage (heritage objects and territories and archaeological sites). For this reason, an environmental impact assessment was carried out, which can determine very precisely whether a railway can be developed in the planned area, if so, under what technical parameters, and, most importantly, what measures must be taken to reduce the negative impact on the environment and public health.	[3,24,26]
Q6 Military Mobility	Ensures efficient transportation of military equipment and strengthens defense readiness. The criteria describe the duration of military equipment transportation; loading time; loading capabilities; the size of cargo storage areas; accessibility by other modes of transport; distance to freight train stations and yards, military training grounds, and other destination points; and adaptability for dual military and civilian purposes.	[5,23,27,28]
Q7 Resilience and reliability of the transport system	Compliance with the criteria of transport system resilience and reliability increases the stability of Lithuania’s transport system, reduces dependence on road transport, and ensures resistance to geopolitical and technological threats. The criteria describe the level of dependence on road transport, the level of resistance to technological threats, and the level of resistance to geopolitical threats.	[20,29]

One of the simplest methods applicable is the Kendall Method [30]. Ranking is performed pursuant to the criteria list, i.e., when the highest rank is given by an expert to the most important criterion, i.e., place or score equal to one. The second most important criterion is given a rank equal to two, the third one is given a rank of three, etc. The last rank receives the lowest value of ranking. This method is logical and easily applicable in practical calculations Jakimavičius et al. [31].

Kendall concordance coefficient [30] is linked with the sum of rank of each factor $R_j$ and with regard to respondents or experts:

$$R_j={\sum }_{i=1}^n{R}_{ij} (\mathrm{j}=1,2,\dots ,\mathrm{m}),$$

(1)

The mean rank of each factor $\overline{R}$ is obtained by dividing the sum of ranks assigned thereto by the number of factors:

$$\overline{R}={\displaystyle \frac{{\sum }_{j=1}^m{R}_j}{m}}.$$

(2)

where $R_{ij}$—rank given by expert i to factor j, n—number of experts (i = 1, 2, …, n), and m—number of factors (j = 1, 2, …, m).

The difference between sum ${\sum }_{i=1}^n{R}_{ij}$ of ranks R_ij and constant quantity ${\displaystyle \frac{1}{2}}n\left(m+1\right)$ is calculated for each criterion:

$${\sum }_{i=1}^n{R}_{ij}-{\displaystyle \frac{n\left(m+1\right)}{2}}.$$

(3)

The square of the difference between ranks’ sum ${\sum }_{i=1}^n{R}_{ij}$ and constant quantity ${\displaystyle \frac{n\left(m+1\right)}{2}}$ is calculated:

$${\left. [{\sum }_{i=1}^n{R}_{ij}-{\displaystyle \frac{1}{2}}n\left(m+1\right)\right]}^2.$$

(4)

Upon calculation as per Formulas (1)–(4), the next step is to calculate the concordance coefficient $W$:

$$W={\displaystyle \frac{12S}{n^2(m^3-m)}}.$$

(5)

Significance of concordance coefficient and compatibility of expert evaluation of factor groups is determined by ${\chi }^2$:

$${\chi }^2={\displaystyle \frac{12S}{nm\left(m+1\right)}}.$$

(6)

Min value of the concordance coefficient $W_{\min }$ is calculated from Formula (7):

$${W{\displaystyle \frac{{\chi }_{v,\alpha }^2}{n\left(m-1\right)}}}_{min}$$

(7)

where ${\chi }_{\nu ,\alpha }^2$—Pearson critical statistics, whose value is found in the table [32], taking the degree of freedom v = m − 1 and significance level α.

3. Results

Ten experts with over 15 years of professional experience in railway, road, and urban planning, design, construction, and operation participated in the survey. The experts were selected to form a well-rounded and representative group capable of assessing the development of the 1435 mm standard gauge railway and the parameters defining it, performing conceptual planning, and conducting initial need justification to final implementation and operation. The number of experts was determined based on their comparable long-term experience in the relevant field and their ability to provide balanced insights across different stages of railway development. Their backgrounds span academia, industry, and government, ensuring diversity and reducing the risk of subjectivity in the AHP weighting process. Moreover, the selection of 10 experts aligns with established practices in AHP-based studies, where expert panels typically range from 5 to 15 participants. This number strikes a balance between diverse perspectives and effective consensus-building.

To this end, three experts from the scientific field with extensive and recognized international experience in the development of railway and road engineering science were included in the expert group. Four experts had experience in the planning and design of 1435 mm gauge railways, with experience in planning and designing major international railway projects in the Baltic States (Rail Baltica project), as well as in the Balkan countries and Spain. The expert group included one expert in construction organization and management with experience in the technical supervision and management of the construction of railways, roads, and large infrastructure projects in Lithuania, Latvia, and Saudi Arabia. The expert group also included two railway operation experts with experience in the operation and maintenance of railway infrastructure, power supply, traffic management, control, and signaling. Individual surveys of these experts, hereinafter referred to as E1–E10, gave results about the importance of criteria that can be observed in Table 2.

Table 2. Criteria group ranks awarded by each expert.

	Q1	Q2	Q3	Q4	Q5	Q6	Q7
E1	1	6	4	2	5	3	7
E2	7	5	4	2	3	6	1
E3	4	3	2	5	6	1	7
E4	1	4	2	5	6	3	7
E5	3	2	6	7	5	1	4
E6	2	5	1	6	4	3	7
E7	1	4	3	7	6	2	5
E8	6	7	1	3	5	2	4
E9	5	4	2	3	6	1	7
E10	4	6	3	2	5	1	7

The outcome from 10 expert surveys was that the Military Mobility criteria group should be adjusted first (0.204), second place—Infrastructure Development (0.186), third place—Economy and Market Conditions (0.164), fourth place—Technological progress (0.136), fifth place—Social Benefit (0.121); other criteria weights for the sustainable development and integration of the different 1435 mm and 1520 mm gauge rail systems are provided in Figure 1.

Figure 1. Determined criteria group weights.

According to the results achieved, the priority criteria groups were identified for the sustainable development and integration of the 1435 mm gauge rail system, when significant constraints exist, such as environmental, protected areas, heritage areas, densely urbanized areas, or insufficient financial resources. The following should be noted:

The first priority criteria group is Military Mobility (0.204). The criteria in this group are designed to ensure the efficient transport of military equipment and the defensive readiness of allies. The main physical criteria are the maximum load capacity of railway viaducts and bridges and the load capacity of railway tracks. Also, to ensure military mobility, it is essential to have enough freight stations with tracks of the required length, trans-shipment terminals allowing military equipment to be transferred from rail to road transport (ramps and cranes), as well as facilities for temporary storage of military equipment (parking lots and container storing areas).

The second priority criteria group is Infrastructure Development (0.186). This is the most significant criterion group in terms of the 1435 mm gauge railway system’s sustainable development. All mentioned group criteria—such as infrastructure, energy supply, and command control and signaling subsystems criteria—have the biggest influence on the railway infrastructure’s performance (traffic speed, safety, and management) and correspond to the railway system supply pattern. The criteria for this group also influence the criteria for other prioritized groups—Military Mobility, Technological Progress, and even Economic and Market conditions in terms of traffic capacity.

The third priority criteria group is Economy and Market Conditions (0.164), which determines railway system services demand parameters—passenger traffic volume and freight traffic volume. A total of 1435 mm gauge railway system demand (traffic volumes) parameters are expressed by smaller parameters, such as passenger train length, passenger travel time, freight train length, freight transportation (carriage) time, and timeline parameters.

The fourth priority criteria group is Technological Progress (0.136), which consists of the three main subgroups of the parameters: safety, travel speed, and environmental friendliness. Additionally, all other subsequent parameters should be discussed, which are similar in purpose to the parameters mentioned, but according to the survey results, have lower importance. Such parameters could be the usable length of freight station tracks, passenger station tracks, and passenger platforms. Notably, these parameters have crucial importance for railway infrastructure performance and effectiveness.

The fifth priority criteria group is Social Benefit (0.121), which corresponds to the importance of the social benefit criteria for 1435 mm gauge railway system development. Social benefit criteria, by their nature, are similar to the Economy and Market Conditions criteria group and therefore express the railway system demand side.

4. Discussion

4.1. Military Mobility

According to the calculations, the group of Military Mobility criteria received the highest number of expert scores. This choice was determined by the very complex geopolitical situation—the proximity of unfriendly countries Russia and Belarus, as well as Russia’s illegal military actions and annexation of Ukraine.

1435 mm gauge rail transport is one of the most important modes of transport for ensuring military mobility. The main advantages of this mode of transport are the suitability of the railway infrastructure for the transport of heavy military equipment and the fast and safe transport of military equipment to carry out planned military tasks at the right time.

According to NATO and EU estimates, it is impossible to move the necessary number of troops to a military conflict zone quickly and efficiently without using 1435 mm gauge rail transport. At the NATO summit in Madrid in 2022, it was agreed that 100,000 highly trained troops should be able to be deployed to a conflict zone within 10 days, followed by 200,000 highly trained troops within 30 days. To this end, it is necessary to develop military mobility on 1435 mm gauge railways by creating modern infrastructure capable of receiving allied troops, reducing cross-border bureaucratic formalities, and increasing the capacity of commercial rail carriers to transport heavy military equipment. The developed railway infrastructure is necessary not only in times of military conflict, but also in times of peace as a deterrent, making it clear that military forces can reach the scene of a military conflict efficiently and in the shortest possible time [28].

However, the main factors limiting military mobility are the insufficient density of railway infrastructure in EU countries. In 2021, there were approximately 234,000 km of railway tracks in Europe, 50% of which were in Germany, France, Poland, Italy, and the United Kingdom. In Poland, there were 19,392 km of railway tracks in the same year, 76.5% of which met the required 221 kN axle load requirement. The report also notes the lack of loading terminals, railway sidings, and ramps suitable for loading military equipment. It is pointed out that it is also necessary to eliminate bottlenecks on main railway lines that restrict the smooth flow of rail traffic [28].

The authors note that in order to increase military mobility, it is necessary to develop not only railway infrastructure, but also innovative railway systems. One of the main priorities is to implement the European Rail Traffic Management System (ERTMS). This system makes it possible to maximize the safety of rail transport, increase the capacity of the railway infrastructure, and harmonize traffic rules in different countries, enabling carriers from different countries to transport passengers and freight [23].

In order to ensure military mobility, it is not only necessary for an ally to have adequate railway infrastructure, but also that the railway infrastructure must be properly maintained and managed, i.e., it must be suitable and ready for military mobility purposes at any time.

4.2. Infrastructure Development

In EU Member States, requirements for the development of 1435 mm gauge railway infrastructure are laid down in Commission Regulation (EU) No. 1299/2014 of 18 November 2014 on the technical specifications for interoperability of the infrastructure subsystem of the rail system in the European Union, selecting them according to the category of the railway line [22]. In addition, the design of the Rail Baltica project infrastructure is subject to the Rail Baltica Design Guidelines [33], which were developed in accordance with the best practices for the design of 1435 mm gauge railways with speeds of up to 249 km/h in other EU Member States.

The criteria for 1435 mm gauge infrastructure development cannot be changed under normal planning and design conditions, as their application is linked to railway safety, environmental impact, and the basic principles of railway system operation throughout the EU rail network. Particular attention should be paid to the parameters of the track gauge and axle load, also known as essential requirements, as they directly determine which trains can run on a railway line and are therefore considered non-modifiable.

However, in exceptional cases, infrastructure parameters—operational characteristics (railway line speed, usable platform length, etc.) may be changed in areas where it is impossible to meet these technical requirements (e.g., in urban areas). Such changes require a comprehensive assessment of possible alternatives and the separate consent of the infrastructure manager [33].

The main problem with applying infrastructure criteria is that it is not always possible to apply them according to the category of the railway line. The most common reasons for this are densely urbanized areas, negative impact on the environment and public health, protected areas, and cultural heritage. It should be noted that railway development cannot always be carried out solely in undeveloped areas that are not subject to protection requirements. In such cases, railway development would lose its main purpose, i.e., to transport passengers and freight to a specific planned location according to specific needs at a specific time. For example, the construction of passenger stations intended to connect two large cities further away from the cities they connect, as well as the construction of freight stations or terminals further away from industrial areas or already developed freight railway stations and their junctions, in accordance with the established requirements and without applying any relaxation thereof, may lead to the passenger and freight transport forecasts on which the economic justification for the project is based as not being achieved and the project not being financially or economically viable (profitable). Therefore, in such cases, to achieve the economic objectives of the project, it is necessary to derogate the requirements so that the requirements selected and applied are optimal for the local conditions.

4.3. Economy and Market Conditions

The group of Economic and Market Conditions criteria was assessed as one of the most important. This was due to the fact that the criteria in this group describe the main needs for railway development—the supply of the railway system and demand among its users [16].

The supply of the railway system is determined by the technical parameters of the railway system, which together define the capacity of the system during a specific period of use. Such criteria are the performance criteria of the railway system—passenger and freight transport capacity, speed, and route conformity to client needs.

Meanwhile, the demand for the railway system is determined by generalized and derived parameters, such as the need to transport a certain number of passengers and freight during a certain period (passenger and freight transport forecast). Notably, the balance between supply and demand identifies the economically optimal parameters of the railway system.

Other criteria in this group that are also very important are the conditions for market access for passenger and freight carriers, i.e., the possibility of obtaining permits to transport passengers and freight at specific times, and the cost of using the infrastructure.

4.4. Technological Progress

The main criteria used to measure technological progress are the same as those used to describe infrastructure development. However, technological criteria and the requirements for their achievement are more focused on improving the efficiency of the railway system. In recent years, particularly significant progress has been made in the areas of railway traffic management and control, signaling, railway communications, and energy supply.

Technological progress criteria contribute significantly to the main requirements for the railway system: reducing passenger travel and freight transportation times, increasing punctuality, improving traffic safety, reducing energy consumption, and, accordingly, reducing the negative impact on the environment. These criteria for technological progress are aimed at improving the accuracy and efficiency of the railway system. Technological progress criteria are inseparable from the use of battery trains, hydrogen fuel cells, and the hybridization of diesel and electric locomotives. The possibilities of installing photovoltaic cells on the surface of noise reduction walls and on the superstructure of the railway (sleepers) have been tested for the production of electricity for railway traction during recent years. In the event of insufficient funding, the possibility of using rolling stock with a variable gauge system in the Rail Baltica railway network is assessed.

Technological progress is also inextricably linked to the development of Information and Communications Technologies (ICT) in the European rail transport sector. First and foremost, the European Rail Traffic Management System (ERTMS) is a standardized train control and management system consisting of the European Train Control System (ETCS) and the GSM-R radio communication system. It should be noted that even the GSM-R system is planned to be replaced by the Future Rail Model Communication System (FRMCS).

The development of 5G communications and the digitization of railway procedural documents are also important. The development of Information and Communications Technologies (ICT) is linked to the reduction in bureaucratic procedures that have a significant negative impact on railway operations and military mobility [23,25].

4.5. Social Benefit

Social Benefit criteria are particularly important when selecting the optimal railway line route. It should be noted that the location and alignment of the future railway line have the greatest impact on the social development of the region within the project area (employee mobility, reduction in unemployment, creation of new jobs in the region, integration of people with disabilities and people living in poverty, and growth of the region’s added economic development) [15,17,18,19].

The Social Benefit criteria, as well as the criteria of the economic and market conditions group, define the demand for railway infrastructure, based on which the optimal criteria and characteristics for railway infrastructure development can be selected (railway line speed, train and platform length, number of railway tracks, station configuration, etc.).

4.6. Sustainability and Ecology

The use of sustainability and environmental criteria in the development of the 1435 mm gauge railway can be applied in two ways. First is the aspect that 1435 mm gauge railway is a green transport mode offering positive environmental benefits, such as reduction in petroleum product usage; efficient use of energy; use of renewable energy sources; and reduction in the negative impact of road and air transport on the environment and public health, such as air pollution, greenhouse gas emissions, and traffic noise. It should be noted that all positive benefits are gained by shifting passenger and freight traffic volumes from conventional 1520 mm gauge non-electrified railways and road transport.

The next aspect is the inevitable negative impact on the environment and public health during the development of the 1435 mm gauge railway. This negative impact is also widely acknowledged. This is particularly the case when the railway is planned in the vicinity of residential areas or environmentally sensitive areas, or in some exceptional cases, inside such areas.

During such cases, one of the main negative impacts of the railway is the negative impact on the environment and public health due to increased noise and vibration levels, the division of natural and residential areas, and changes to the landscape, which have a negative impact on protected nature and heritage objects.

It is generally and legally agreed, despite its significance, that railways should not cross densely populated areas, cemeteries, or public areas, or destroy protected areas and cultural heritage sites. Therefore, the competent authorities and the public are involved in the assessment of all the above criteria, and the established procedures for strategic environmental impact assessment, environmental impact assessment, and Natura 2000 significance assessment are applied [16,24].

Notably, in all cases, a balance based on the principles of sustainable 1435 mm gauge railway development must be found between the Economic and Market conditions criteria should be found. Such a balance should determine the optimal parameters of railway infrastructure for passenger and freight transportation in equilibrium with Sustainability and Ecology criteria.

4.7. Resilience and Reliability of the Transport System

Before the assessment of the resilience and reliability of the transport system criteria of the 1435 mm gauge railway system, it is first necessary to note the ability of this railway system to provide a higher level of service compared to the 1520 mm railway system, as well as the greater ability of this system to withstand, absorb, and adapt to disruptions or accidents and recover quickly.

In the development of the 1435 mm gauge railway, the resilience of the railway system is assessed as a comprehensive system indicator covering characteristics that reflect the state of the system: vulnerability, survival, response, and recovery. Additional proactive (preventive) characteristics that contribute to system resilience are risk reduction and preparedness.

In the development of 1435 mm gauge railways, the resilience and reliability of the railway system are enhanced by the European Rail Traffic Management System (ERTMS) used in the standard railway system and by uniform and standardized traffic control rules. These measures help to ensure greater traffic safety and punctuality of train services [20,29].

In addition, the expansion of the standard railway gauge to 1435 mm ensures disconnection from the 1520 mm gauge railway system used in unfriendly and militarily aggressive neighboring countries and the information and communications technologies (ICT) used to organize its traffic, such as the GLONASS navigation system, common traffic management, signaling, freight and passenger transport systems, and rules.

5. Conclusions

All groups of criteria assessed in the study are important for the development and subsequent operation of the 1435 mm gauge railway system. Based on the results of the study and the analysis of scientific articles, the groups of criteria evaluated could be divided into two major categories describing the demand and supply of the railway system.

The criteria groups of Economic and Market Conditions, Military Mobility, and Social Benefits should be analyzed to determine the demand for the railway system. The criteria in these groups mainly describe the needs of the railway system, expressed in terms of passenger and freight transport volumes and the required passenger travel and freight transport times. These criteria are also expressed in terms of economic and social benefits (regional economic growth, reduction in social disparities and unemployment, integration of socially excluded regions and populations, and enhancement of national defense and deterrence).

Another major category, which is the most important in terms of infrastructure and technology, is the category of criteria groups that describe the supply of the railway system. This category includes the criteria groups of Infrastructure Development, Technological Progress, and Transport System Resilience and Reliability.

It should be noted that the balance between the criteria in the demand and supply categories for the 1435 mm gauge railway system defines the optimal criteria for both railway infrastructure supply and railway infrastructure demand, expressed in terms of passenger and freight traffic intensity. However, this theoretical balance may be influenced in practical conditions by Sustainability and Environmental criteria. In densely urbanized areas or areas sensitive to environmental protection, the criteria in this group may limit the possibilities to apply the Infrastructure Development and Technological Progress criteria.

Similarly, the feasibility of the Infrastructure Development and Technological Progress criteria may be limited by a lack of funding and short project implementation time, which were not assessed separately in this study.

According to the experts who participated in the study, when setting priorities for the development of a 1435 mm gauge railway system, it is most important to take into account the criteria of the Military Mobility group and the criteria of Economic and Market conditions, which define the main needs for freight and passenger transport services, i.e., the projected passenger and freight transport volumes and the parameters (passenger train length, passenger travel time, freight train length, freight carriage time, and transportation (carriage) service timeline) defining them.

According to the experts who participated in the study, the most important criteria for the development of a 1435 mm gauge railway system, which determines the supply of the railway system, belong to the groups of Infrastructure Development criteria and Technological Progress criteria.

This study found that the implementation of the criteria in the Technological Progress criteria group ensures partial implementation of the Transport System Resilience and Reliability Criteria in the development of the 1435 mm gauge railway, which explains why it was rated as the least important in the expert survey despite its crucial significance.

Although this criterion was rated as the least important in the expert survey, its overall significance remains crucial. Sustainability and environmental criteria were also placed in the lower importance group, but it is important to note that this study found that the criteria in this group can influence the standard Infrastructure Development and Technological Progress criteria and may initiate a derogation procedure for their requirements. The relatively low importance assigned could be explained by the fact that the railway’s contribution to sustainable transportation development, as well as its role in reducing air pollution and mitigating climate change, is widely recognized and indisputable. All possible negative impacts—such as noise, vibration, and deforestation—are typically addressed during environmental assessment procedures, which are mandatory for railway development in most cases.

In this study, the focus was placed on evaluating the importance of criteria related to the technical and developmental parameters of different railway systems. Therefore, financial and economic evaluation criteria—such as logistics costs, traffic volume, or return on investment—were not analyzed in detail. We acknowledge that the sole use of expert opinion has certain limitations, especially regarding empirical verification. While professional judgments serve as useful indicators of technology and strategic drivers, future studies will aim to include empirical inputs, i.e., traffic flow and cost factors, to enhance the strengths and applicability of the framework. Incorporating such empirical data will assist in cross-verifying expert-based results and support data-informed decision making in railway development planning.

Subsequent scientific research should examine in more detail the principles and conditions under which derogation from standard technical development parameters may be necessary, such as restrictions imposed by protected areas, cultural heritage sites, complex terrain, unsuitable geological conditions, physical constraints in densely urbanized areas, or limited funding. More empirical data should also be applied in the analysis. Such research should result in the development of a model and practical methodology for the sustainable development of 1435 mm gauge railways, which could be applied by responsible authorities and railway operators.

Subsequent scientific research should examine in more detail the principles and conditions for derogation procedures of standard technical development parameters when their implementation is impossible due to restrictions imposed by protected areas, cultural heritage sites, complex terrain, unsuitable geological conditions, physical constraints in densely urbanized areas, or limited funding. More empirical data for the analysis should be applied as well. Such scientific research should result in a model and practical methodology preparation for 1435 mm gauge railway sustainable development, which could be applied by responsible authorities and railway operators.