In-Depth Lifecycle Assessment of Ballasted Railway Track and Slab Track Considering Varying Subsoil Conditions
Round 1
Reviewer 1 Report
This paper aims to compare slab track and ballasted railway track using LCA. I suggest authors improve paper based on the below comments:
1- Abstract needs improvement, please elaborate findings.
2-Goals and scenarios are not well explained., please explain table 1. and your scenarios.
3-I cannot understand why different soil conditions may have difference in both ballasted and slab tracks CO2 emission.
4-Have you consider that ballast layer should be changed each 10 years
5-Please make conclusion bullet pints and elaborate.
Author Response
Thank you very much for your helpful questions and comments to improve our paper. We hope you appreciate that we extensively improved the quality and clarity of the English language. Please find specific improvements as answers to your specific questions/comments.
(1) Abstract needs improvement, please elaborate findings.
We completely re-wrote the abstract to improve quality and clarity. In addition, we added a short explanation for the findings and quantitative results.
(2) Goals and scenarios are not well explained., please explain table 1. and your scenarios.
Please find a clear overview of methodology and goals within Chart 1), which is described in lines 148-152. The scenarios and details of table 2 are described in lines 287-324.
(3) I cannot understand why different soil conditions may have difference in both ballasted and slab tracks CO2 emission.
We improved highlighting the research gap at the end of the introduction (lines 131-146) which also includes an explanation as to why different soil reinforcement measures are necessary for ballasted track and slab track in case of medium or poor subsoil. The quantification of these measures can be found in table 2. These measures lead to different masses (transport and production) and construction processes which results in higher emissions.
(4) Have you consider that ballast layer should be changed each 10 years
We improved the elaboration on the data basis for service life and maintenance demands of the different construction types (lines 161-183; “standard elements”). This is data we established and improved with ÖBB since decades (based on historical documentations, track data analytics and in working groups). For Austrian boundary conditions on newly build main lines (track components – including under sleeper pads and asphalt layer, ballast quality and traffic load characteristics) there is no need for ballast cleaning during track’s service life of 43 years. In Austria, ballast cleaning is only executed as part of a renewal measure at the end of service life – expect for turnout areas with high traffic loads and single points like crossings or bridge approaches. This is also valid for other countries like Switzerland where we also implemented the methodology of standard elements. We know that this very much depends on ballast quality, dewatering system and substructure quality, so this is definitely not the case for every country. We addressed this issue within the limitations in the conclusion (lines 414-419) highlighting that the results are valid for Austria and similar boundary conditions.
(5) Please make conclusion bullet pints and elaborate.
We implemented your suggestion in the conclusion to add clarity to the presentation of our findings.
Reviewer 2 Report
In-depth life cycle assessment of ballasted railway track and slab track considering demands for subsoil conditions
The purpose of this study is to evaluate and compare the life cycle greenhouse gas (GHG) emissions of two different track structure types: common ballasted track and so-called slab track. The results show that ballast track is associated with 11–20% lower life cycle GHG emissions, where by the variation in relative emission reduction is associated with different soil conditions.
The research results can provide some reference for choosing common ballasted track or slab track in engineering. The structure of the article is generally complete, and the research method is reliable, but it still has some problems. The questions are as follows:
(1) Simplify the introduction. The introduction can be simplified by deleting some repetitive information and unnecessary details about specific research. The focus is to provide a concise overview of the research gaps and the objectives of this study.
(2) In the calculation of life cycle greenhouse gas (GHG) emissions for a track with a long operating time, the maintenance phase is bound to be a very necessary research stage. Is it a bit arbitrary for the author to directly exclude this stage?
(3) “Except for the tunnel, the relative GWP of slab track emissions is always higher than that of ballasted track.” The author should give the reasons why the conclusions obtained under the tunnel condition are different from those under other working conditions.
(4) “Some values for calculating emissions of various construction processes are taken 195 from the literature [24].” The calculation value of emissions in the construction process is affected by many factors. Is the data in the literature universal?
(5) Is the greenhouse gas emission of the whole life cycle of the project construction related to the construction organization form in the construction process ? The article does not calculate or explain the greenhouse gas emission value when calculating it.
(6) In this paper, the calculation of GWP values for four scenarios does not give detailed calculation steps, but directly gives the results after introducing relevant technical data, which is not accepted.
(7) This paper evaluates the life cycle greenhouse gas (GHG) emissions of two different types of track structures from theoretical data. In order to ensure the authenticity and accuracy of the evaluation results, the life cycle greenhouse gas (GHG) emissions of two different types of track structures should be evaluated based on the actual engineering case data.
(8) “The service life for the asphalt layer is defined by using a factor based on the track service life”， What is the basis for this?
(9) In the results part, the author should focus more clearly on the most important findings, and ensure that no data analysis is carried out in the conclusion part, so as to maintain very descriptive and informative. All explanatory content should be moved to the subsequent discussion section.
(10) The discussion section currently only discusses further emission reduction measures. It can be clearly explained why it is important to assess the life cycle greenhouse gas (GHG) emissions of two different track structure types and how to contribute to future engineering applications.
It should be Extensive editing.
Author Response
Thank you very much for your helpful questions and comments to improve our paper. We hope you appreciate that we extensively improved the quality and clarity of the English language. Please find specific improvements as answers to your specific questions/comments.
The structure of the article is generally complete, and the research method is reliable, but it still has some problems. The questions are as follows:
(1) Simplify the introduction. The introduction can be simplified by deleting some repetitive information and unnecessary details about specific research. The focus is to provide a concise overview of the research gaps and the objectives of this study.
We implemented your suggestion by extensively re-writing and re-arranging the introduction.
(2) In the calculation of life cycle greenhouse gas (GHG) emissions for a track with a long operating time, the maintenance phase is bound to be a very necessary research stage. Is it a bit arbitrary for the author to directly exclude this stage?
The statement regarding the importance of the maintenance phase is absolutely true which is why it is included in our study. Only in regards to data from environmental product declarations we neglect data on the use phase (which is mostly MND “module not declared” anyways) as we calculate the use phase ourselves. Track work is calculated via equation 1.
(3) “Except for the tunnel, the relative GWP of slab track emissions is always higher than that of ballasted track.” The author should give the reasons why the conclusions obtained under the tunnel condition are different from those under other working conditions.
There is no need for soil reinforcement measures in tunnel areas since the tunneling sole already provides a homogenous and settlement-free base. Since slab track (less to no maintainability in case of settlements) has higher demands on its supporting layers, this has more positive effects on slab track than for ballasted track. We included the explanation within the introduction (basic understanding and research gaps), the methodology (explanation of scenarios) as well as in the result section.
(4) “Some values for calculating emissions of various construction processes are taken 195 from the literature [24].” The calculation value of emissions in the construction process is affected by many factors. Is the data in the literature universal?
We included a table (table 1) elaborating on gathered data and sources in regard to emission factors for materials and processes for more clarity and transparency. Data for construction processes are mainly elaborated on our own according to Equation 1 (you can find also the quote to a paper of ours where we explain this process in detail) for, some are taken as universal data from literature according Table 1.
(5) Is the greenhouse gas emission of the whole life cycle of the project construction related to the construction organization form in the construction process ? The article does not calculate or explain the greenhouse gas emission value when calculating it.
The calculations are based on the standardized design of Austrian Federal Railways as well as typical transport lengths. For design of slab track, we use case data from currently built section in Austria. For ballasted track, we use case data of existing mainlines within the Austrian Federal Railways network. Expected service lives and maintenance demands are developed in cooperation with Austrian Federal Railways as part of the methodology “standard elements” since 2005. We improved the according elaborations within the methods section.
(6) In this paper, the calculation of GWP values for four scenarios does not give detailed calculation steps, but directly gives the results after introducing relevant technical data, which is not accepted.
We included a table (table 1) elaborating on gathered data and sources in regard to emission factors for materials and processes for more clarity and transparency.
(7) This paper evaluates the life cycle greenhouse gas (GHG) emissions of two different types of track structures from theoretical data. In order to ensure the authenticity and accuracy of the evaluation results, the life cycle greenhouse gas (GHG) emissions of two different types of track structures should be evaluated based on the actual engineering case data.
We do use actual engineering case data – elaborations see question/suggestion 5.
(8) “The service life for the asphalt layer is defined by using a factor based on the track service life”， What is the basis for this?
Usually, the asphalt layer in Austria is designed to last two service lives, hence factor “2”. This means that ballast/sleepers or the slab track plates can be renewed without changing the asphalt layer. After the second service life, the layer is worn out and has to be renewed as well. In case of bad pre-existing soil conditions there are more and heterogenous settlements in the substructure underneath the asphalt layer due to the induced traffic loads. This leads to increased wear, which is the reason why the asphalt layer has to be renewed as well after 60 (slab) and 43 (ballasted) years.
(9) In the results part, the author should focus more clearly on the most important findings, and ensure that no data analysis is carried out in the conclusion part, so as to maintain very descriptive and informative. All explanatory content should be moved to the subsequent discussion section.
We followed your suggestion and moved explanatory content to the discussion section.
(10) The discussion section currently only discusses further emission reduction measures. It can be clearly explained why it is important to assess the life cycle greenhouse gas (GHG) emissions of two different track structure types and how to contribute to future engineering applications.
We improved by highlighting these aspects in the introduction and conclusion section.
Reviewer 3 Report
In-depth life cycle assessment of ballasted railway track and slab track considering demands for subsoil conditions
Abstract
· The authors are recommended to display the basic methodology and findings in a quantitative manner.
introduction
· Literature review should be extended and some suggested studies can enhance the review.
· Road Materials and Pavement Design, Volume 23, 2022 - Issue 2, https://doi.org/10.1080/14680629.2020.1826347, innovative infrastructure solutions, 4, 5(2019), https://doi.org/10.1007/s41062-018-0190-z
· Research innovation should be stated at the end of previous studies
· The research gap should be highlighted.
· The research objectives are not clear.
Methods
· The authors should rethink about the display method in a simplified way. Flowchart may be added to summaries the methodology.
The sub-headings
· Calculations. Transport, materials, processes. Please simplify those sections and it may be combined in one section.
· The provided data in table 1, what are the basic for these values? Why the authors use design of 60, and 43 years. Please clarify the criteria for the selection of values of these parameters.
· Please delete table 2 it is already provided in Figure 3.
· Please compare the findings of this study with previous studies.
· How can this idea be useful for the designers engineers?
Conclusion:
· The authors should give their findings in a quantitative manner.
· A recommendations to the practitioners should be added. Also a limitation of the current study should be highlighted.
should be improved and simplifed
Author Response
Thank you very much for your helpful questions and comments to improve our paper. We hope you appreciate that we extensively improved the quality and clarity of the English language. Please find specific improvements as answers to your specific questions/comments.
Abstract
(1) The authors are recommended to display the basic methodology and findings in a quantitative manner.
We completely re-wrote the abstract to improve quality and clarity. In addition, we added a short explanation for the findings and quantitative results.
introduction
(2) Literature review should be extended and some suggested studies can enhance the review.
Road Materials and Pavement Design, Volume 23, 2022 - Issue 2, https://doi.org/10.1080/14680629.2020.1826347, innovative infrastructure solutions, 4, 5(2019), https://doi.org/10.1007/s41062-018-0190-z
Thank you for the input which we included in the conclusions for highlighting GHG reduction potentials (lines 425-427).
(3) Research innovation should be stated at the end of previous studies; The research gap should be highlighted; The research objectives are not clear.
We improved highlighting the research gap at the end of the introduction (lines 131-146) and stated research innovations at the end of previous studies.
Methods
(4) The authors should rethink about the display method in a simplified way. Flowchart may be added to summaries the methodology.
Please find a clear overview of methodology and goals within Chart 1.
(5) The sub-headings: Calculations. Transport, materials, processes. Please simplify those sections and it may be combined in one section.
We followed your suggestions regarding the subheadings and improved clarity and simplicity in that section.
(6) The provided data in table 1, what are the basic for these values? Why the authors use design of 60, and 43 years. Please clarify the criteria for the selection of values of these parameters.
We improved the elaboration on the data basis for service life and maintenance demands of the different construction types (lines 161-183; “standard elements”). This is data we established and improved with ÖBB since decades (based on historical documentations, track data analytics and in working groups). For Austrian boundary conditions on newly build main lines (track components – including under sleeper pads and asphalt layer, ballast quality and traffic load characteristics) there is no need for ballast cleaning during track’s service life of 43 years.
(7) Please delete table 2 it is already provided in Figure 3.
We deleted (former) table 2.
(8) Please compare the findings of this study with previous studies.
We included a comparison within the discussion section.
(9) How can this idea be useful for the designers engineers?
Previous studies and comparisons of track construction assume optimal subsoil conditions. However, in reality, pre-existing soil conditions are heterogeneous and may be bad in some sections. This is why we included varying subsoil conditions within our study to help engineers to identify the optimal solutions for apparent in-situ conditions. We included the recommendations in the conclusion.
Conclusion:
(10) The authors should give their findings in a quantitative manner.
We improved by choosing bullet points and quantitative figures in the conclusion.
(11) A recommendations to the practitioners should be added. Also a limitation of the current study should be highlighted.
We included the recommendations in the conclusion and discussed limitations.
Reviewer 4 Report
Manuscript ID: sustainability-2544244
Tittle: In-depth life cycle assessment of ballasted railway track and slab track considering demands for subsoil conditions
Dear authors , I would like to thanks the authors and please consider the following comments:
1- Please specify the inovativity of your study.
2- As the tittle of the manuscript has “subsoil condition” but there is no result of the soil condition in abstract and the conclusion part.
3- How have you decided on the parameters of best or poor soil? Based on which code or study?
4- The results need to be quantified and also shown in the abstract part.
5- Explain more about how the equation 1 of is extracted.
6- Explain about the process of designing the slab or ballasted track.
7- In the paper “subsoil conditions” needs more study and results.
8- Please specify the reference for: “Austrian boundary conditions and for trains 124 that reached a speed of 250 km/h.”.
English editing needs at each sentence carefully, and making sure that it's well designed and serves its purpose.
Author Response
Thank you very much for your helpful questions and comments to improve our paper. We hope you appreciate that we extensively improved the quality and clarity of the English language. Please find specific improvements as answers to your specific questions/comments.
(1) Please specify the inovativity of your study.
We clarified the innovations of our study within the introduction section.
(2) As the tittle of the manuscript has “subsoil condition” but there is no result of the soil condition in abstract and the conclusion part.
We included the figures in a quantitative manner within the abstract and the conclusion part.
(3) How have you decided on the parameters of best or poor soil? Based on which code or study?
The parameters are based on experience by Austrian Federal Railways within the “standard elements” methodology which is now explained in more detail in the methods part. “Poor soil” is seen as soil with negative effects on load distribution and track structure. We included a description in the methods sections (lines 290-303).
(4) The results need to be quantified and also shown in the abstract part.
We improved by describing results in the abstract in a more quantitative manner.
(5) Explain more about how the equation 1 of is extracted.
We improved clarity of the description of equation 1.
(6) Explain about the process of designing the slab or ballasted track.
The design of ballasted and slab track is chosen according to Austrian Federal Railways standardized track designs. We were not part of the designing process.
(7) In the paper “subsoil conditions” needs more study and results.
We included an in-depth description within the methods sections (lines 290-303).
(8) Please specify the reference for: “Austrian boundary conditions and for trains that reached a speed of 250 km/h.”.
We specified and improved clarity for this reference. The study is based on infrastructure that is design for up to 250 km/h which is the maximum design speed in Austria. Also track sections planned up to 2040 limit its design speed at 250 km/h.
Round 2
Reviewer 2 Report
The purpose of this study is to evaluate and compare the life cycle greenhouse gas (GHG) emissions of two different track structure types: common ballasted track and so-called slab track. The results show that ballast track is associated with 11–20% lower life cycle GHG emissions, where by the variation in relative emission reduction is associated with different soil conditions.
The article has a clear overall context after the author 's modification, which can well explain the in-depth life cycle assessment of ballasted track and slab track considering the needs of foundation conditions, and has certain guiding significance for the construction of ballasted track and slab track. The research results can provide some reference for choosing common ballasted track or slab track in engineering. The structure of the article is generally complete, and the research method is reliable，qualified to publish in Sustainability.
Author Response
Thank you for your feedback. We appreciate your recommendation to publish our article!
Reviewer 3 Report
The authors addressed the reviewer comments
Author Response
Thank you for your feedback on our revisions. We are pleased to learn that we were able to meet your requirements!
Reviewer 4 Report
Dear the author
Thanks for revised manuscript and considering the mentioned comments.
Author Response
Thank you for your feedback on our revisions. We are pleased to learn that we were able to meet your requirements!
