Life Cycle Assessment of High-Performance Railway Infrastructure, Analysis of Superstructures in Tunnels and on Open Tracks

Abstract

Almost 25% of the environmental pollution, measured by the indicator of global greenhouse emissions, is emitted by transport. Changes in the mobility behavior of the population will be essential if the 17 UN Sustainable Development Goals (SDGs) and the goals of the EU Commission’s Green Deal are to be attained. Accordingly, the existing infrastructure has to transform into a sustainable transport infrastructure through further optimizations in the future. Therefore, continuous optimizations and improvements of designs, materials, and processes are crucial to achieving long-term sustainability. This study investigates different superstructures with the method of life cycle assessment using the example of the emerging high-performance infrastructure at the Brenner Base Tunnel (BBT). The study analyzes all relevant life cycle stages (A1–C4) and validates different effects of service lifetimes of superstructure elements on the open track and in the tunnel. The results, which are presented in the form of GWP, AP, and NRCED, show that there is environmental reduction potential, especially in the stage of use. As more frequent modernization cycles and the associated remanufacturing of superstructure elements account for a significant proportion of the total environmental impact, lifetime extending optimization of products yields improvements in the ecological footprint.

1. Introduction

The idea of sustainability has also taken part in infrastructural construction [1,2,3]. The call for sustainable development from an ecological, economic, and social point of view is becoming louder and louder [1].

How does sustainable building work? Sustainable building means that the entire construction is investigated, and every detail/every product is analyzed and considered throughout its life cycle from raw materials supply, construction, use, disposal, and removal [1]. By taking all relevant processes into account, resources and energy quantities can be optimally used, reduced, and saved in every life cycle stage [4,5].

However, sustainability does play an essential role in the building sector, as in the infrastructure sector, where ecological, economic, and social assessments get more and more applied [1,2,3]. In the near future, sustainability will play a major role in managing and solving problems regarding climate change, energy transition, mobility transition, decarbonization, etc. [6]. Today’s sustainable (traffic-) infrastructure covers themes ranging from traditional touchpoints such as transportation and resource consumption to issues of environmental quality and human health [2,3,6].

The eco-friendly trains and the enhanced interoperability between road and rail through the formation of Trans-European Transport Networks (TEN-T), in particular, make a significant contribution to achieving the sustainability goals of the EU and UN [7,8,9]. The Brenner Base Tunnel, which is located in the Scandinavian-Mediterranean (ScanMed) corridor of the TEN core network [7,9], is an example of the benefits of high-performance rail infrastructures [10,11]. For example, in the foreseeable future, freight trains will reach Austria from Italy over low gradients and without change in the train composition (length, weight, amount of locomotives) [7]. The change in the modal shift (from road to rail) is obvious, resulting in environmental benefits from reduced truck traffic. Passenger trains will cross the Alps in about 25 min at speeds over 200 km/h, which will also result in a modal shift (from road to rail or from plane to rail) [7,12,13].

However, such projects place great demands on the involved parties, the construction, the materials used, and the operation and maintenance. Therefore, continuous improvements, optimizations, and network developments are necessary to contribute to a future-proof and sustainable European transport infrastructure in the near future through the Trans-European Network and the strengthened road-rail interoperability [14].

The Life Cycle Assessment (LCA), according to ISO 14040 [15] and ISO 14044 [16], is an internationally standardized and common method for assessing the environmental effects of products and product systems over their life cycle [15,17,18]. Because the LCA method offers a transparent, verifiable, and comprehensible system for describing and evaluating environmental impacts [17,18], LCA tools are often applied to help stakeholders to select environmentally appropriate materials and designs and provide information for decision-makers [15,18,19]. The LCA also presents optimization potentials or provides results for the environmental labeling of products [15,17,18].

To support the decision-making process, this LCA study pursues the goal of examining the ecological potential of various common as well as new types of superstructures (ballasted track with concrete sleeper and slab track) for railroads in tunnels and on open tracks [20,21,22,23,24,25] taking the Brenner Corridor and the Brenner Base Tunnel as examples of an emerging high-performing infrastructure.

In the wake of this basic research, the sustainability assessment is limited to ecological aspects only. Economic, social, and operational aspects are not taken into account.

Furthermore, the ecological study is intended to assess the environmental impacts of a 1 km railroad and completely focuses on the significant ecological outcomes. The results are displayed by means of selected indicators such as Global Warming Potential (GWP), Acidification Potential (AP), and Non-Renewable Cumulative Energy Demand (NRCED) in order to ensure a clear and readable form of every respective superstructure type. Hence, the identification of possible optimization areas is more comprehensible. On the other hand, the basic research study aims to serve for further planning on the Brenner Corridor. Furthermore, the study is intended to provide a basis for possible follow-up studies at the Brenner Base Tunnel or other large-scale railroad projects. The study should therefore support further future railroad LCA studies or LCA of materials used in the railroad sector along the TEN core network or in Austria.

Specific attention is paid to the investigation of the impacts of service lives with different simulated time periods of 80 and 200 years and a variation of the minimum and maximum service life over the entire life cycle (A1–C4). Such variations are mainly intended to validate the impact of product lifetimes and to demonstrate the importance of the environmental impacts of new production/remanufacturing. Moreover, it is intended to determine the effects of shorter and longer lifetimes of products. Based on the investigations, possible ecological potentials of various superstructures, as well as individual components, will be identified and presented for each life cycle stage. The results are presented and discussed on the basis of the “Production Stage” (A1–A3), “Construction Process Stage” (A4–A5), “Use Stage” (B2–B5), and the “End of Life Stage” (C1–C4).

2. Superstructures in Austria

In Austria, rail traffic operates in mixed traffic (freight and passenger traffic) on standard gauge (1435 mm) with a 600 mm sleeper spacing and a maximum axle load of 22.5 tons, which is common in many parts of Europe [25]. The Austrian regulations of the Federal Railways (ÖBB) [23,24,25] distinguish between two main types of railroad superstructures in the Austrian railroad network: the ballasted track [23] and the slab track [24]. The guidelines specify the approved superstructure components and also define their use for the respective track grade and track speed [25].

2.1. The Superstructure Body

The superstructure of the railroad forms the track for rail-bound vehicles [26]. The superstructure and its components absorb the vertical and horizontal forces generated by the trains and wagons rolling over it and hold the bogies or wheelsets on the rails to keep them spaced to the correct gauge [26,27].

From a traffic, operational, and technical point of view, at least the following requirements [26,27] have to be placed on the superstructure, therefore:

• Safety with a low probability of damage
• Trouble free and available system
• Economical with low maintenance requirements
• Permanent, i.e., as long as possible
• High ride comfort
• Low noise and vibration pollution
• Sustainable

The superstructure includes all components of the track (rail- and switch-linkage, rails, sleepers/track supporting plates, rail fastenings, underlay plates, and intermediate layers), the bedding of the track grid (e.g., ballasted track), and the protective layers [26].

2.2. Differences between Ballasted Track and Slab Track

The differences between the two railway superstructures (ballasted track, slab track) are in the bedding [27,28]. For ballasted track superstructures, the track grid floats in the ballast bed. Therefore, there is no fixed anchoring of the sleepers to the ballast. The loads caused by the rolling wheels are transferred to the subgrade via the rails, sleepers, and ballast [26,29].

In contrast, the slab track uses concrete track base plates to transfer the load [22]. The load carrying is, therefore, more uniformly distributed [22,27,28]. A durable and low-maintenance track is thereby guaranteed [27,28].

The different properties of the superstructures result in different practical applications. The Austrian ballasted track is mainly used on open tracks due to its simple manufacture and maintenance [23]. In Austria, the slab track is mainly used in tunnels of greater length (≥500 m) due to its more complex construction and higher costs [23,28].

In addition to the fundamental differences in the design of the superstructure, the service life is of great importance [23,24,27,28]. Especially the service life is decisive for the subsequent examination and the results. The common lifetimes [23,24,30,31] are listed in

Table 1. Usual lifetimes of sleepers and slab tracks in the Austrian rail network.

Superstructure Element	Usual Lifetimes
Sleeper	30–40 years
Slab Track	80–100 years

below. These service life ranges are intended to show the effects of different track conditions (gradients, multiple curve sections, etc.) and are taken into account to map worst- and best-case scenarios in terms of maintenance operations and replacements. Further explanations are available in Section 2.3.

2.3. Manufacturing, Construction, and Maintenance Processes

As mentioned, most of the superstructure components used on the Austrian network are produced by Austrian manufacturers. In preview to Section 3, the products are largely transported by train to the construction site.

The initial installation, as well as maintenance work and component replacement, are conducted on high-performance lines or high-ranking lines in the Austrian network using track-laying machines and a few conventional construction machines. In the regular situation, a machine-assisted strategy is followed.

After finishing the subgrade protection layer, the superstructure building process starts. After the ballast has been partially spread, the rails, sleepers, and other parts, such as rail fasteners, are laid and installed in the correct position by using a track-laying train, a welding robot, a tamping machine, dynamic rail stabilizer, and a rail grinding machine.

In the tunnel, the workflow is pretty similar. However, the prefabricated track support slabs can be mounted directly on the tunnel floor spindled up to the correct position, and get fixed by using grouted concrete. Lifting and installation in the tunnel are usually realized by mobile portal cranes or mobile cranes and concrete mixers or concrete pumps.

Once the slab track is on the open track, nearly the same procedures are used, but without the difficulties of confined conditions. The only difference is the preliminary construction of a load distribution plate on the embankment below the grouted concrete layer.

In the case of maintenance, on the one hand, processes such as rail grinding are carried out in periodic cycles, and on the other hand, defective or superstructure components that have reached the end of their service life are replaced by new ones. These maintenance processes are fully machine-assisted in the case of the ballasted track and slab track variants. The final demolition is also affected by using track-laying machines and conventional construction machinery at the construction site, such as trains and trucks, for transport. The following table details the machines employed.

During the entire lifetime or review period, a wide range of maintenance work and renewals are necessary for the rail superstructure. These operations are related to machine actions in

Table 2. Machines used during construction, maintenance, and deconstruction processes.

Machine	Model	Engine Power [kW]	Performance Rate [m/h]	Superstructure Type
Ballast bed cleaning machine	RM900VB	1566	70	ballast track
Track laying machine	P95SR	600	200	ballast track
Tamping machine	CSM09-3X	440	350	ballast track
Dynamic rail stabilizer	DGS62N	370	350	ballast track
Welding machine	AMS100	300	602	ballast and slab track
Rail grinding machine	default	300	300	ballast and slab track
Locomotive	BR203	1305	100,000	ballast and slab track
Gravel plow	R24	440	2000	ballast track
Portal crane	Donelli PTH350	140	70	slab track
Concrete mixer	default	400	220	slab track
Concrete pump	default	100	220	slab track
Truck mounted crane	default	100	62	slab track
Excavator	R928	300	24	slab track
Truck	default	300	24	ballast and slab track

.

In this case,

Table 3. Work operations depending on route conditions/lifetimes.

Action/Renewal	Min. Period (Years)	Max. Period (Years)
Tamping and Straightening	4	5
Grinding	1	3
Ballast bed cleaning	12	20
Ballast bed renewal	20	30
Rail renewal	10	15
Sleeper renewal	30	40
Fastener renewal	10	30
Slab Track renewal	80	100

lists the necessary maintenance work depending on and considering a minimum and maximum maintenance scenario according to experiences from the ÖBB- network. The minimum period reflects the maximum maintenance effort and is assumed to be the minimum product service life. Therefore, the products reach their service life earlier. Similar assumptions are made for maintenance activities such as rail grinding. In the maximum period, the prevailing track conditions are optimal and therefore require low maintenance efforts or product replacements.

3. Life Cycle Assessment of Selected Superstructures

3.1. Goal

This study was performed to analyze different Austrian railway track systems based on an analysis of environmental potentials. Therefore, three common Austrian ballasted tracks with different concrete sleepers with under sleeper pads and one slab track system (ST) were evaluated on a fictitious but representative section of an Austrian high-performance railway track on the open track and in the tunnel. The primary study goal was to evaluate and localize environmental impacts per lifecycle stage, component category, and the entire lifecycle. The LCA study also considers different simulation periods, such as 80 and 200 years, and a variation of the minimum and maximum lifetimes to outline the effects of several maintenance cycles, product replacements, and overall influences. Regarding the variation of lifetimes, as mentioned above, there is a better illustration of different route conditions. This approach using the different lifetimes and the simulated time periods of 80 and 200 years was chosen to provide a better understanding of the impacts and the maintenance strategies of the railroad.

Therefore, the target of the study was, therefore, to identify and localize the optimization potentials of railway superstructures as basic research in order to form a benchmark for further investigations and follow-up studies.

3.2. Scope of the Study

3.2.1. Functional Unit

The functional unit is defined for the provision of 1 km of track or superstructure. In addition, standards are concretized according to the guidelines of the Austrian Federal Railways (ÖBB) [23,24,25,29], local conditions, and other aspects, which are listed below:

• Single-track line
• The considered section is in a straight line;

  a.

  Route rank S+ or S

  b.

  v_max ≥ 160 km/h

• Line load > 50,000 tons per day
• Rail profile: 60E1
• Rail steel grade: R 260
• The substructure is always in good condition.

3.2.2. System Boundaries

Within the scope of the study, the “cradle to cradle” approach with a “closed-loop recycling” method was used due to the fact that, according to the Austrian Federal Railways, the components of the railroad infrastructure can only be partially reused for high-performance lines. Only 40% of the concrete elements, 50% of the rails, and 30% of the track ballast can be recycled. The other components or percentages are sent to landfill or disposal.

All life cycle stages from the raw material supply (A1) to the disposal (C4), exclusively the utilization of energy use or train traffic (B1, B6, B7, B8), were considered in the assessment. Therefore, all processes related to the maintenance and new production of superstructure components were considered in the analysis.

Regarding the primary raw materials used, they obtain from mostly Austrian suppliers and are widely transported by trains or occasionally by lorries. It should be mentioned that certain products are manufactured outside of Austria [32,33]. These are largely modeled using generic data corresponding to the EU or DACH region because of difficult data procurement. If certain datasets are not available, they are also considered by means of these generic data from the ecoinvent v.3.8 database [34].

As a technical system boundary, this study is defined by the subgrade protection layer or tunnel floor. The subgrade protection layer represents the boundary between the superstructure and the subgrade [26,27,28]. The tunnel floor constitutes the boundary between the track and the tunnel structure in the tunnel variant [22]. In reality, the condition of the subgrade or tunnel floor has a significant effect on the condition of the superstructure [26,27,28]. To simplify matters, it is assumed that the condition of the subgrade or tunnel floor does not change during the review period and is always in good condition.

Hence, deterioration of the superstructure condition due to the substructure or changes to the tunnel structure is neglected by focusing completely on the superstructure components [35]. As a result, the risks of deterioration, for example, of the tunnel structure, are not considered and are not part of this investigation. The effects on the ecological potential detection of the superstructure are thereby not influenced by a changing substructure condition.

Depending on the project design, the process cycle, the strategy of the Austrian Federal Railways, and the life cycle stages defined by EN 15804 + A2 [36] show the system boundaries and considered stages of the assessment (see Figure 1).

In addition to the technical system boundaries of the study, the Austrian national boundary is defined as the geographical system boundary since the essential primary data originate from this geographical area [35]. The study itself is therefore carried out on a fictitious track body in the ÖBB-network [23,24,25] on the emerging Brenner Corridor or on the Austrian part of the Brenner Base Tunnel [7].

3.3. Life Cycle Inventory (LCI)

The following life cycle inventory of the various superstructure components and processes is largely based on specific data. Data such as concrete mixtures, raw material supply, recipes, manufacturing processes, and amounts of energy and water consumption were gathered by data collections from manufacturers and rail operators. If relevant specific data was not available or could not be collected in the course of processing, generic data from the “ecoinvent 3.8” database [34] was used.

The transport distances of primary materials (concrete sleepers 1: 320 km, concrete sleeper 2 and 3: 520 km, slab track: 520 km, rails: 385 km, ballast: 15 km, grouted concrete/other concrete products: 10 km, rail fastener: 730–935 km, under sleeper pads/other elastic layers: 765–1170 km) were computed with the Brenner Base Tunnel as the final destination. The transport distances of non-specific preliminary products, where no exact distances were available, “market”-ecoinvent-datasets [34] were taken into account. These datasets include the average distribution distance and represent the real market situation [34]. The materials are mostly transported by rail. Cargo trains with electrically powered locomotives on the Austrian rail network are generally assumed. However, some logistical operations are realized by truck transports. It is expected that EURO 6 trucks will be used for this purpose. For this, the energy and fuel consumption is based on the respective ecoinvent 3.8 datasets [34].

Machinery and manufacturing/renewal process information was obtained from data provided or from the literature [14,26,27,37,38] and was modeled accordingly for the analysis.

The modeling of the Life Cycle Inventory (LCI) and its calculation is realized with the software SimaPro 9.3.0.3. SimaPro enables the user to take all processes (inputs and outputs) into account, such as the extraction of raw materials, and, if necessary, to allocate different processes proportionally [39].

However, the selection of data was such in a way that the real situation in Austria got modeled as best as possible.

The specific data used in this study is not available for public distribution in detail because of confidential reasons and company secrets. The product names are anonymized, and only a sample of data is displayed in

Table 4. Life Cycle Inventory of the main superstructure elements.

Name	Amount	Unit
Ballast Sleeper 1 and 2	2140	m3/km
Ballast Sleeper 3	1960	m3/km
Sleeper 1	282	kg/Sleeper
Concrete C50/60	0.120	m3/Sleeper
Reinforcement	7.2	kg/Sleeper
Under Sleeper Pads	4.9	kg/Sleeper
Sleeper 2	320	kg/Sleeper
Concrete C60/75	0.120	kg/Sleeper
Reinforcement	8.1	kg/Sleeper
Under Sleeper Pads	5.2	kg/Sleeper
Sleeper 3	320	kg/Sleeper
Concrete C60/75	0.13	kg/Sleeper
Reinforcement	5.3	kg/Sleeper
Under Sleeper Pads	4.6	kg/Sleeper
Slab Track	5000	kg/Track support plate
Concrete C30/37	2.0	m3/Track support plate
Reinforcement	300	kg/Track support plate
Grouting Concrete C25/30	1.2	m3/Track support plate
Reinforcement Grouting Concrete	20	kg/Track support plate
Load Distribution Plate C25/30	0.84	m3/m
Reinforcement Load Distribution Plate	10.5	kg/m
Rails 60E1	60.21	kg/m
Rail Fastener W14	2.78	kg/pc
Rail Fastener W300-1	7.95	kg/pc
Intermediate Plate ZW700	0.45	kg/pc

below.

3.4. Life Cycle Impact Assessment (LCIA)

To assess the environmental impacts and optimization potentials of 1 km of railroad superstructure, the indicators of Global Warming Potential—GWP (kg CO₂ equivalent), Acidification Potential—AP (mol H+ equivalent), and Non-Renewable Cumulative Energy Demand—nrCED (MJ equivalent), used in the Environmental Product Declarations (EN 15804 [36]), were considered as in other relevant infrastructure assessments [14,40,41,42,43,44].

In the following, the results of the respective superstructures (expenses, emissions, etc.), as well as the processes of the life cycle stages, are presented accordingly, starting from the life cycle impact assessment [15].

Faced with an ever-expanding list of indicators, decision-makers are challenged to understand LCA results. Therefore, LCA practitioners are challeged to effectively and comprehensibly communicate results and minimize the number of indicators presented [45].

4. Results

The results are presented per impact indicator in terms of GWP, AP, and NRCED per each individual life cycle stage as well as in an overview of all lifecycle phases according to GWP per track kilometer in absolute numbers and also as distribution in percent.

For this purpose, a variation of minimum and maximum lifetimes and simulated periods (80 and 200 years) are displayed as an analysis for five types of superstructures studied. In detail, the component levels show the environmental impact of each material used.

4.1. Results for the Entire Life Cycle

Basically, the LCA results (Figure 2) have shown that the stages of production and maintenance have the greatest impact on the environment. It is precisely the stage of use (B2-B5) that emits the most to the natural environment. This environmental impact is not caused by the operation (B1 or B8) of the railroad but by the limited lifetime of the respective products. Once a service life or the maximum possible service life has been reached, the component has to be replaced. The period between maintenance work or rebuilds shapes the effects on the environment since these are always coupled with manufacturing, construction, transport, and disposal processes of the new superstructure components to be installed and removed. These processes during utilization are considered according to EN 15804 (6.2.4) [36] within the results of the utilization phase B2–B5. The life cycle stages of the construction (A4–A5) and disposal (C1–C4) account for only a minor share of the environmental impacts of the entire life cycle and can be quantified to about 3%. This small proportion yields from the lower emissions during the construction process stage (A4–A5) and its way of manufacturing (train-bound or conventional). The low environmental contribution in the end-of-life stage (C1–C4) can be quantified by the high reuse quote and the recycling.

Depending on the superstructure system, the percentage distributions of the environmental impacts of the entire life cycle occur once more in the initial stage of production or the stage of use in the course of modernization processes (see Figure 3).

In the case of the ballasted track system (Figure 3a), the environmental response was relatively low in the production phase (A1–A3) but higher in the stage of use (B2–B5) due to the increased maintenance effort. For the slab track (Figure 3b), emissions were significantly higher than for the ballasted track in phases A1–A3 but lower in the use phase. This difference between ballasted track and the slab track arises due to the greater effort and material input in the production phase and minor maintenance effort in the use stage.

Examining the different lifetimes of the superstructure products, as explained in Section 2.2 and Section 2.3 above, reveals the major differences in the maintenance effort and the replacement activities (see Table 3) in the use stage B2–B5. Figure 4 shows all the investigated superstructure variants during the life cycle. The variation with the minimum and maximum service life is compared in order to highlight the differences. As mentioned above, a variation of the different lifetimes was considered to cover any various track conditions (gradients, multiple curve sequences, etc.).

The GWP results show that the sleepers and track support plates with the increased service life can consequently remain in the track body for a longer period, and therefore the maintenance effort is lower. This effect and the reduced number of replacements are reflected in the amount of CO₂ eq. emitted. An extension of the service life, for example, the concrete sleepers of 10 years or, in the case of the slab track of 20 years, results in a minimizing of the GWP of about 31%. In absolute numbers, a reduction of approx. 1100 tons of CO₂ eq. over a period of 80 years is achieved.

Equal conclusions emerge by comparing the variants with the simulation period of 200 years. Therefore, the longer service life of each superstructure element has a positive effect on the amount of environmental pollution and results in less maintenance effort.

For this reason, only the variants with the maximum lifetime are discussed in more detail in Section 4.3.

4.2. Product Stage (A1–A3)

By taking a closer look at the individual life cycle stages, the environmental impact of every single superstructure element can be displayed. Figure 5 shows the impact to the indicators GWP, AP, and NRCED of the sleepers, and Figure 6 and Figure 7 for the slab track system in the tunnel and on the open track.

In the case of the ballasted track (Figure 4), it can be seen that the rails account for the largest share of the environmental impact in production, at around 50%. This is followed by the sleeper or under sleeper pad with approx. 10%. The production of the track ballast amounts to approx. 6% of the GWP. In contrast, the percentage distribution in the case of the slab track shifts a little (Figure 6 and Figure 7). Here, the concrete materials (track support plate, grouted concrete, and load distribution plate) contribute approx. 45% of the effects on the environment. The rails can be quantified at about 40%.

In general, it is already apparent in this life cycle stage that there is potential for ecological optimization of the superstructure elements at the material level or in the manufacturing process. To address the particular areas, the environmental impacts of rail production/steel production could be reduced in all impact categories if the production gets optimized. Additionally, the concrete materials show potential for optimization. Rather than going into detail about the optimization, the aim of the study was to detect and determine the potential improvement areas. In this respect, we refer to further detailed material science and further studies. However, such a construction change must not be a detriment to the strength and durability of the product.

4.3. Stage of Use (B2–B5)

As already explained in Section 4.1, the stage of use accounts for the largest share of environmental impacts over the entire life cycle. The service life of every superstructure element is the “amplifier” of environmental influences and is, therefore, essential for sustainability. Logically, the components of the superstructure can remain in the track body for a longer time if the service life lasts for a longer period. During this usage, there is no significant impact on the environment. However, if parts of the superstructure get modernized or substituted, this replacement is associated in each case with machine operations, manufacturing and transport processes for the new components, installation, removal, and final disposal. Due to the fact that each replaced product (e.g., concrete sleepers, rails, etc.) is technologically identical to the first installed products, the values from production do not change compared to those mentioned in Section 4.2. For this reason, a precise itemization at the component level is omitted in Section 4.3. Therefore, only the effects per life cycle phase are presented.

Depending on the superstructure system (ballasted track or slab track), several modernization cycles are run through in the respective period under consideration of 80 or 200 years. This result is corresponds to environmental impacts. In particular, the manufacture of new superstructure elements accounts for the largest share of the stage of use (B2–B5). Figure 8, Figure 9 and Figure 10 illustrate this once again for the simulated period of 80 years for the ballasted and slab track.

In particular, the rails are responsible for a significant environmental impact in the stage of use. This can be explained by the fact that the rail on high-loaded lines (high-performance infrastructure) has a relatively short service life compared with other superstructure components, and therefore these elements have to be replaced frequently, i.e., the rails take a great value of the environmental effects. This cognition is also shown by the comparison of the life cycle using the example with the simulated period of 80 years with and without rails (see Figure 11).

Hiding the rails demonstrates that the slab track has no environmental impact during its service life in the selected simulation of 80 years, as the service life of the slab track has not been reached yet. In the case of the ballasted track, on the other hand, several modernization cycles are run through. However, in total, the greater number of environmental impacts of the slab track will occur in the life cycle stage A1–A3 and get compensated by the low maintenance effort over the life cycle.

4.4. Discussing the Areas of Application in Tunnels and on Open Tracks

The results previously (see Figure 11a) have shown that the ballasted track and slab track have almost the same environmental impacts on the open track. The ballasted track performs at the open track about 0.5% better than the slab track variant.

In the tunnel, the slab track system was analyzed. For tunnels with lengths ≥ 500 m, this system is justifiably preferred over ballasted tracks. Due to the elimination of the load distribution plate, the effects on the environment are approx. 11 % lower than with a ballasted track. Thus, it can be concluded that the regulations of the Austrian Federal Railways regarding the use of slab tracks in tunnels of greater length (≥500 m) definitely make sense, also from an ecological perspective.

To summarize, an ecological recommendation can be made for the ballasted track on the open track, as it performs slightly better. In the tunnel, the slab track is preferable from an ecological and operational perspective.

5. Conclusions

The aim of this study was to support the further planning of the Brenner Base Tunnel and the Brenner Corridor but also to provide strategies for the ecological optimization of the elements of the railroad superstructure. This way, the study should be a small step towards achieving the sustainability goals of the EU and the UN and represents a baseline study for sustainable TEN tracks. It is, moreover, a further study using the specific example of the Brenner Corridor and aids in the overall consideration of the section at the Brenner Base Tunnel (BBT). Previously, BBT studies have always been conducted on the shift of traffic (from road to rail), or assessments of the tunnel construction excluding the tracks were analyzed. This study thus offers the possibility to close another research gap and consider the roadway as well. In this context, the previous studies are used to provide a basis for the further ongoing planning of the ScanMed corridor via further life cycle assessments or evaluations, which make a comprehensive mapping of the corridor possible in the future.

According to the results, it can be mentioned that there is potential for optimization, especially in the stage of use (B2–B5). Results have shown that more frequent modernization cycles and the associated remanufacturing of superstructure elements account for a significant proportion of the total environmental impact. By using best- and worst-case scenarios, the study identified that extending the service life of superstructure components results in savings of around 31% in CO₂ equivalents and lower maintenance efforts. The environmental impact could be reduced by optimizing the products for a longer and more durable service life, which would proceed in longer maintenance intervals. I.e., there is a reduction in using new products in terms of replacement processes in the use stage (B2–B5). The possible increase in environmental impacts due to possible design changes (e.g., larger concrete volume, dimensional changes, etc.) in the manufacturing stage (A1–A3) will be compensated by a longer service life in the stage of use (B2–B5) and will lead to general overall savings. The difference between the environmental impact of a “traditional” and an “optimized” structure will be emphasized regarding its service life in the future: The longer the service life, the lower the impacts [42,46]. Similarly, other studies [42,46] on the construction sector have reported CO₂ savings and reduction of impacts through life cycle extensions and design optimizations.

At the product stage (A1–A3), the investigation has shown that the rails are responsible for about 40–50% of the GWP, the sleepers for about 10% in the case of the ballasted track and the track support slab, grouted concrete and load distribution slab for about 45% in the case of the slab track variant. Finally, the steel and concrete products are localized as the main drivers in stages A1 to A3 and have to be investigated at least in further follow-up studies in terms of possible ecological material optimizations. Although the aim of this study was not to undertake detailed material investigations and material optimizations, it was to highlight the possible areas for improvement. As an example, the reduction of the cement content, based on the current research [46], seems to be a possibility to limit the environmental impacts of concrete products. However, in this context, we would refer to further research results and future investigations. According to the open tracks, the ballasted track and the slab track put nearly the same load on the environment. The ballasted track performs slightly better. That’s why a purely ecological recommendation can be made for the ballasted track on the open tracks.

For tunnels, the slab track is the best ecological choice assuming the low environmental impacts. Here the load distribution slab is not required. The amount of GWP could be reduced for the concrete elements in tunnels to about 28% in A1 to A3.

This study showed that stages A4–A5 and C1–C4 are not mainly responsible for a large amount of environmental pollution because of the low emissions in the installation or construction processes regarding the high reuse quotes and the recycling.

To summarize, it can be claimed that the present study analyzes the fundamental environmental impacts in the course of the construction, operation, and demolition of railroad superstructures using the example of the high-performance track on the Brenner Corridor. Possible potentials of fundamental ecological optimizations of the superstructures were identified, considering two simulation periods (80 and 200 years), as well as minimum and maximum lifetimes, and various topics, such as service life extensions, possible material, and (manufacturing) process optimizations, were outlined. Of course, not all questions could be answered in detail, and not all the possible relevant facts/findings could be analyzed in detail. Effects of changing subgrade conditions or changes in the tunnel structure were not considered over the years because of focusing on the superstructure elements in order to localize and determine fundamental optimization potentials on the superstructure. However, these cognitions have to be further verified in follow-up studies to verify further environmental potentials to provide an entire assessment of the corridor track line. Moreover, this basic investigation was based in its analysis only on a life cycle assessment and thus disregarded the topics of economy, as well as social aspects. Beyond that, it would be interesting to include the monetary and social impacts in further analysis in order to be able to present a holistic sustainability assessment. For the development of general global strategies, it is essential that further economic and social aspects are included in future studies. In conclusion, any change that contributes to a future-proof and sustainable built environment is valuable for generations in the future and our living space. In this respect, the railway as an environmentally friendly means of transport already plays a major role in sustainable European transport infrastructure and will continue to do so in the future.