Rail Transit Networks and Network Motifs: A Review and Research Agenda

Round 1

Reviewer 1 Report

The concept of this study and its realization are well. The problem is presented clearly. The findings are connected with the results. The topic of rail transit networks and network motifs was realized, however, from a specific point of view. I personally miss its reflections on the connections of the rail network form with the settlement structure of a country or a city. The real inter-city networks differ between countries like France or Spain (centric network) and like Germany or Poland (grid). Similar differences can be observed on the local levels (mono- or polycentric agglomerations). Perhaps will be sensible to add some thoughts and comments about this point of view?

Evaluating this manuscript highly in general, I formulated some remarks to improve the quality and readability.

There is a lack of information about the period of publication search. When limited to the newest positions – explain why. When not limited – also explain such an assumption.

When the literature search was prepared? I see the newest positions from 2021. Now, we have 2024 and the basis should be refreshed.

I have reservations about the selection of the database. For example, using search keywords “rail transit network” and “network structure” on “mdpi” website I win 31 search positions including 14 papers newer than 2021 and 10 papers from the journal “Sustainability”.

I recommend revising and refreshing the literature base.

The word “sustainability” creates the next remark. This word does not exist in the whole text (except the list of references). Meanwhile, the will to publish in a specific journal creates the need to profile the research and its content to the topics of the journal. So, I strongly recommend adding some sentences and findings in the introduction and in conclusion commenting on the connectivity with the term “sustainability”.

Some technical remarks are below.

The fonts in figure 1 could be bigger and thus more readable.

Figure 3 – it is not clear what part of the figure represents description b) and c).

I think that the sentence shouldn’t start with the indication of the literature source and continue next with a small letter (see example line 140). This sentence (and much more in the next part of the manuscript) should be reformulated, for example to: “The study [38] builts a general…” or “In [38] the Authors built a general…” etc.

What means [54? ] in line 486?

Minor editing of English language required.

Author Response

The concept of this study and its realization are well. The problem is presented clearly. The findings are connected with the results. The topic of rail transit networks and network motifs was realized, however, from a specific point of view. I personally miss its reflections on the connections of the rail network form with the settlement structure of a country or a city. The real inter-city networks differ between countries like France or Spain (centric network) and like Germany or Poland (grid). Similar differences can be observed on the local levels (mono- or polycentric agglomerations). Perhaps will be sensible to add some thoughts and comments about this point of view?

Thanks for your comment. Centric- and grid-like rail transit networks, either at country or local level, represent different network structures at the global level. Examining differences at the local level through network motif analysis between rail transit networks of different global structure is a theme subject to investigation. We have added this remark at the beginning of section 6 of the new version of the manuscript.

Evaluating this manuscript highly in general, I formulated some remarks to improve the quality and readability.

There is a lack of information about the period of publication search. When limited to the newest positions – explain why. When not limited – also explain such an assumption.

In the Materials and Methods section of the new version of the manuscript, we have pointed out that the search of articles did not impose temporal limitations, meaning that we do not discard articles for being published at an early date. Research on network motifs was triggered by Milo et al. (2002) article, so most of the analyzed literature goes later than 2002.

When the literature search was prepared? I see the newest positions from 2021. Now, we have 2024 and the basis should be refreshed.

I have reservations about the selection of the database. For example, using search keywords “rail transit network” and “network structure” on “mdpi” website I win 31 search positions including 14 papers newer than 2021 and 10 papers from the journal “Sustainability”.

I recommend revising and refreshing the literature base.

Thanks for the remark. The initial search of articles arrived to 2021, so we needed to revise and refresh the base of articles to examine. We have examined 19 new references, of which we have included 11 in the literature review. Most of these references dealt with motif detection and use of motifs on different fields. Another block of references examined network robustness on rail transit networks.

The word “sustainability” creates the next remark. This word does not exist in the whole text (except the list of references). Meanwhile, the will to publish in a specific journal creates the need to profile the research and its content to the topics of the journal. So, I strongly recommend adding some sentences and findings in the introduction and in conclusion commenting on the connectivity with the term “sustainability”.

Thanks for your remark, which has also been raised by the editorial team of Sustainability. Following your advice, we have discussed the implications to sustainability of the present research. We have also mentioned sustainability implications in the article abstract.

Some technical remarks are below.

The fonts in figure 1 could be bigger and thus more readable.

Thank you for your suggestion. We have enlarged the fonts of Figure 1 for better readability.

Figure 3 – it is not clear what part of the figure represents description b) and c).

Following the suggestion of other reviewer, we have removed figures 3 and 4 from the manuscript.

I think that the sentence shouldn’t start with the indication of the literature source and continue next with a small letter (see example line 140). This sentence (and much more in the next part of the manuscript) should be reformulated, for example to: “The study [38] builts a general…” or “In [38] the Authors built a general…” etc.

Thanks for your remark. We have rephrased all sentences starting with a reference key.

What means [54? ] in line 486

That was a misspelled bibtex reference. We have corrected that in this new version.

Reviewer 2 Report

 INTRODUCTION

1. Please reformulate the first sentence, as railway is part of transport infrastructure, so it is inappropriate to say that competes with it.

2. While this section is generally clear, a more comprehensive definition of “network motifs” would be appropriate.

MATERIALS AND METHODS

The primary methodology employed in this paper appears to be an extensive literature review.

3. However, the section only presents the part regarding the selection of the articles that will be reviewed and does not give details about the analysis methodology. Please complete this section.

THE RAIL TRANSIT INDUSTRY

4. The paragraph from line 187 to line 212 presents aspects that are more related to the network and not to the industry. I suggest revising and moving it to the appropriate chapter.

5. Moreover, consider whether the title of the chapter THE RAIL TRANSIT INDUSTRY accurately reflects the content. I suggest replacing the term "industry".

RAIL TRANSIT NETWORKS

6. In fig. 3 please provide (a), (b), (c), (d) for corresponding networks, not only in figure title.

7. More, what is the purpose of Fig.3? Is it used for further analysis? Do you consider Space-L and Space-P methods to perform a Space-wise network motif analysis? If so, please elaborate. If not, I suggest removing it.

NETWORK MOTIF DETECTION AND ANALYSIS

The topic investigated by the authors is highly relevant. They correctly identify the deficiency in network motif decomposition, which could be used to analyze both unweighted and weighted networks.

A RESEARCH AGENDA OF WETWORK MOTIFS ANALYSIS IN RAIL TRANSIT NETWORKS

8. Please reconsider WETWORK in the title.

9. Also declared that “Based on previous studies on rail transit networks, we propose using Space-P to build the rail transit line network [54? ] and rail transit station network using Space-L” it is not explicitly explained how this can be achieved. Please provide more information.

10. Please reorganize the material as Fig. 7 Typical five-node subgraphs of a transportation network and connected explanations have no place in this chapter, detailing past research.

11. Connect current insights, propose future steps (AGENDA) in a specific, achievable, and relevant manner and be more proactive in suggesting the way forward.

CONCLUSION

12. The authors state what “can” be done and do not go to the next level, the action level, in which to state their vision of the way forward. I  suggest a more in-dept analysis.

Author Response

INTRODUCTION

1. Please reformulate the first sentence, as railway is part of transport infrastructure, so it is inappropriate to say that competes with it.

We have rephrased the first sentence to remove the idea of competition between network infrastructures.

2. While this section is generally clear, a more comprehensive definition of “network motifs” would be appropriate.

Thanks for your remark. In the last paragraph of the introduction we have defined network motifs as patterns of connections between subsets of network nodes which appear in higher frequencies than in an equivalent random network, and we have related them with the local structure of complex networks.

MATERIALS AND METHODS

The primary methodology employed in this paper appears to be an extensive literature review.

3. However, the section only presents the part regarding the selection of the articles that will be reviewed and does not give details about the analysis methodology. Please complete this section.

In this research, the methodological design of the research is mainly focused on the selection of the papers. Once selected, papers have been examined by authors and grouped in the sections presented in the manuscript (see Bešinović (2020) for a paper following a similar methodology). At the end of the methodology section we have added a paragraph indicating how we have grouped the papers, thus complementing the report of the methodology of analysis.

Bešinović, N. (2020). Resilience in railway transport systems: a literature review and research agenda. Transport Reviews, 40(4), 457–478. 

THE RAIL TRANSIT INDUSTRY

4. The paragraph from line 187 to line 212 presents aspects that are more related to the network and not to the industry. I suggest revising and moving it to the appropriate chapter.

Thanks for pointing this out to us. This paragraph presents content related to complex networks theory, so it must be included in Section 4, rather than in Section 3. We have moved these contents to the second paragraph of Section 4.

5. Moreover, consider whether the title of the chapter THE RAIL TRANSIT INDUSTRY accurately reflects the content. I suggest replacing the term "industry".

In this section, we explore the characteristics of rail transit, distinguishing between intercity and urban rail transit. We acknowledge that speaking of “The rail transit industry” may suggest to some readers that we are covering issues related with industrial organization of rail transit. Then, we have decided to relabel this section as “Intercity and urban rail transit”. 

RAIL TRANSIT NETWORKS

6. In fig. 3 please provide (a), (b), (c), (d) for corresponding networks, not only in figure title.

Following the next suggestion, we have removed figure 3.

7. More, what is the purpose of Fig.3? Is it used for further analysis? Do you consider Space-L and Space-P methods to perform a Space-wise network motif analysis? If so, please elaborate. If not, I suggest removing it.

Following your suggestion, we have removed figure 3.

NETWORK MOTIF DETECTION AND ANALYSIS

The topic investigated by the authors is highly relevant. They correctly identify the deficiency in network motif decomposition, which could be used to analyze both unweighted and weighted networks.

A RESEARCH AGENDA OF WETWORK MOTIFS ANALYSIS IN RAIL TRANSIT NETWORKS

8. Please reconsider WETWORK in the title.

We have corrected the typo in the section title. Thanks for pointing this out.

9. Also declared that “Based on previous studies on rail transit networks, we propose using Space-P to build the rail transit line network [54? ] and rail transit station network using Space-L” it is not explicitly explained how this can be achieved. Please provide more information.

In Space-P, nodes are connected if there is at least one route between them, while in Space-L, nodes are connected if they are consecutive stops on a given route. As a result, building the Space-L network is straightforward, as it corresponds with the physical structure of the network. The building of the Space-L network is more complex, as it depends not only on the physical network structure, but also on the itineraries scheduled in a given time window. Once these itineraries are known, it is possible to connect all pairs of nodes with a direct route between them.

10. Please reorganize the material as Fig. 7 Typical five-node subgraphs of a transportation network and connected explanations have no place in this chapter, detailing past research.

Thanks for pointing this out to us. We have moved the paragraph around Fig. 7 and the figure itself to the motif detection section.

11. Connect current insights, propose future steps (AGENDA) in a specific, achievable, and relevant manner and be more proactive in suggesting the way forward.

Thanks for your remark. At the end of each of the three subsections of Section 6, we have proposed specific research lines about weighted and unweighted rail transit networks, and also about network motif decomposition and analysis.

CONCLUSION

12. The authors state what “can” be done and do not go to the next level, the action level, in which to state their vision of the way forward. I  suggest a more in-depth analysis.

Thanks for your remark. We believe that we have accomplished this proposing specific lines of research in Section 6. Nevertheless, we have rephrased the conclusions section to be presented in a more propositive manner.

Round 2

Reviewer 1 Report

I am satisfied with the answers and the corrections. Now, I recommend publishing this manuscript in “Sustainability” in the section “Sustainable transportation”.

Reviewer 2 Report

Thanks to the authors for their cooperation, all my suggestions have been solved. The quality of the material is visibly improved.

Minor editing of English language required.