Public–Private Partnership (PPP) in Road Infrastructure Projects: A Review of Evolution, Approaches, and Prospects

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Overall, this is a will conducted, interesting and relevant study. The literature review is sufficiently comprehensive, and the methodology is appropriate. The authors also properly present the gaps in the study. It is however suggested the authors be invited to consider the following observations:

·        The authors make many references to science in their editorial, yet these often seem unrelated to the subject of the sentence or paragraph and would benefit by an explanation for the usage of the terminology. For instance;

o   Line 55: scientific production of highways

o   Line 135: scientific production in the research on PPPs

o   Line 154: Prices Law on the possible evaluation of scientific production

o   Line 186: total scientific output

o   Line 463: interest arouse by the scientific community

These could all be valid use of the terminology but needs to be explained. For example at Line 463, the context seems to imply the engineering community

·        Line 71 invites the options of scientometrics and bibliometrics. The authors opt for bibliometrics and should explain why the choice selection. Also, scientometrics, as the quantitative study of science doesn’t seem to be a relevant option for this study. Authors could explain why they considered it an option

·        Line 108 introduces the different inclusion/exclusion criteria yet only introduces the first criteria. What were the others? As well, in this paragraph the authors speak of time horizon. Does this mean the period 1993 – 2022?

·        Line 135 speak of scientific production in the research line on PPPs, yet this is not identified as an area of research in Table 3

·        Line 154 introduces Prices law as a possible evaluation tool for scientific production. Need to explain how when the graph only charts publication frequency

·        Prices Law: there is no explanation of why this law is considered a relevant tool in the analysis. Prices Law in essence is that a small number of individuals are responsible for the large portion of results.

·        Line 186 speaks to total scientific output. It is unclear, to me at least what is meant by this statement

·        Tables 4 and 5 identify a relatively narrow time spans (2000 – 2012) and (2000 – 2015) respectively across the 30 years of the study. This merits some discussion, particularly given the rapid growth in published articles in the period from 2007 to 2022

·        As stated above Line 463 introduces interest by the scientific community whereas the context seems to imply the engineering community. Then later at lines 480 – 483 the authors identify the main issues in the published articles as finance and project management

·        The Conclusion offer the Global Financial Crisis and the SDGs as key factors that have driven the increased research activity. They do not cite a reference, and are not otherwise introduced into the body of the article and as such merit more substantive validation

Other observation:

·        Lines 31-33 are repeated at lines 34-36

·        Line 38, missing word “without increasing, safeguarding infrastructure …”

·        Introduction could be expanded to explain in more depth why the increasing interest in PPPs which would better explain why the increased research interest

Author Response

Dear reviewer, the authors would like to thank you for the recommendations made to the original version of the manuscript. The recommendations have been very precise, so the authors have incorporated modifications that we hope will help to comply with these recommendations and contribute to improving the quality of the manuscript for future readers if it is ultimately suitable for publication.

Below, the authors we have organized the different recommendations that have been proposed to us, as well as providing a response to each of them. In case modifications have been required in the manuscript, these are indicated in red.

Question 1. The authors make many references to science in their editorial, yet these often seem unrelated to the subject of the sentence or paragraph and would benefit by an explanation for the usage of the terminology. For instance;

o   Line 55: scientific production of highways

o   Line 135: scientific production in the research on PPPs

o   Line 154: Prices Law on the possible evaluation of scientific production

o   Line 186: total scientific output

o   Line 463: interest arouse by the scientific community

These could all be valid use of the terminology but needs to be explained. For example at Line 463, the context seems to imply the engineering community.

ANSWER 1.  The authors are grateful for their careful review. We regret the typographical errors noted. We want to inform you that all errors were detected and fixed in the new version of the manuscript.

Question 2. Line 71 invites the options of scientometrics and bibliometrics. The authors opt for bibliometrics and should explain why the choice selection. Also, scientometrics, as the quantitative study of science doesn’t seem to be a relevant option for this study. Authors could explain why they considered it an option.

ANSWER 2. The authors report that our research only used the bibliometric analysis method. However, we agree that the wording could be confusing. Therefore, we report that "scientometrics" has been removed to avoid confusion.

Question 3. Line 108 introduces the different inclusion/exclusion criteria yet only introduces the first criteria. What were the others? As well, in this paragraph the authors speak of time horizon. Does this mean the period 1993 – 2022?

ANSWER 3. The recommendation is very appropriate. The inclusion criteria were, first of all, the selected keywords. Then, only research articles were selected, so all other documents were excluded. The time horizon was also limited to include the period 1993-2022, so the rest of the time was excluded. This means that the inclusion criteria were selected to identify the excluded papers.

The authors we consider that Figure 1 explains this procedure. If, after the above explanation, the authors cannot respond to your recommendation, we would be grateful if you could help us improve this aspect in a second round of revision.

Question 4. Line 135 speak of scientific production in the research line on PPPs, yet this is not identified as an area of research in Table 3.

ANSWER 4. Thank you for your comment. The authors we want to explain that in this part of the paper, we are analysing the thematic areas, that is, the groups of experts working on the research line of PPPs in road infrastructure projects belonging to different academic disciplines. We want to highlight that these thematic areas are predefined in Scopus, the repository used for the analysis.

Question 5. Line 154 introduces Prices law as a possible evaluation tool for scientific production. Need to explain how when the graph only charts publication frequency.

ANSWER 5. The authors share your concerns. Thus, we would like to inform you that we have removed any sentence referring to Prices law in the new version of the manuscript.

Question 6. Prices Law: there is no explanation of why this law is considered a relevant tool in the analysis. Prices Law in essence is that a small number of individuals are responsible for the large portion of results.

ANSWER 6. As stated in the previous recommendation, the authors thank you for your recommendation and inform you that any references have been removed in the new version of the manuscript.

Question 7. Line 186 speaks to total scientific output. It is unclear, to me at least what is meant by this statement.

ANSWER 7. Thank you for the recommendation. The authors share the lack of clarity of the statement, so we have rewritten this sentence to make it more accessible in the new version of the manuscript.

Question 8. Tables 4 and 5 identify a relatively narrow time spans (2000 – 2012) and (2000 – 2015) respectively across the 30 years of the study. This merits some discussion, particularly given the rapid growth in published articles in the period from 2007 to 2022.

ANSWER 8. The authors would like to report that we do not understand this recommendation. In Figure 2, the authors find that there are two differentiated periods: 1993-2007 and 2008-2022. We find justification to explain this change in trend and then apply a comparative analysis in some analyses, such as research areas and journals. Table 4 refers to the most cited articles, while Table 5 refers to the most productive authors. In no case do we make a comparison between periods. Table 4 shows the year of publication, while Table 5 shows the first and last year the authors published in the line of research under study.

Consequently, the authors would like to report that we do not understand the scope of the recommendation. Please be more precise in a second round of review, if necessary, so that we can introduce modifications to comply with your recommendation.

Question 9. As stated above Line 463 introduces interest by the scientific community whereas the context seems to imply the engineering community. Then later at lines 480 – 483 the authors identify the main issues in the published articles as finance and project management.

ANSWER 9. Again, we appreciate the comment. It is similar to recommendation 4. The authors would like to highlight that when we talk about PPPs we do so as a line of research, while different groups of academic experts research within it, delimited into research areas. As a result, some aspects have been specifically addressed by engineers, while others have been studied by financiers and project management experts. In order not to create further confusion within the manuscript and given that there is a specific section to address the research areas, we use the generic term scientific community to refer to an expert who is researching in the PPP line of research.

Question 10. The Conclusion offer the Global Financial Crisis and the SDGs as key factors that have driven the increased research activity. They do not cite a reference and are not otherwise introduced into the body of the article and as such merit more substantive validation.

ANSWER 10. This comment is very valuable. In the initial version of the manuscript, the authors did not we indicate these references in the conclusion because they had been previously included in the introduction and results section. However, in the new manuscript version, we have incorporated the bibliographical references to support our conclusions based on previous research.

Question 11.  Lines 31-33 are repeated at lines 34-36.

ANSWER 11. The recommendation is very appropriate. We want to report that we have corrected the typographical error in the new version of the manuscript.

Question 12.  Line 38, missing word “without increasing, safeguarding infrastructure …”

ANSWER 12. The recommendation is very appropriate. We want to report that we have corrected the typographical error in the new version of the manuscript.

Question 13. Introduction could be expanded to explain in more depth why the increasing interest in PPPs which would better explain why the increased research interest.

ANSWER 13. The authors are grateful for this recommendation. We would like to report that we have expanded the academic literature in this section of the paper, trying to widen the research gap and explain what the main contributions of our research are to the previous academic literature.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript titled "Public-private partnership (PPP) in road infrastructure projects: evolution approaches and prospects" presents a comprehensive bibliometric analysis of 734 Scopus-indexed articles on highway PPPs from 1993-2022. This bibliometric analysis identifies the financial management, costs, pricing systems, privatization, and sustainability of transport infrastructure services.

In the methods part, the authors may think of providing more detailed explanations of the bibliometric methods. Please explain the benefit of using the VOSViewer software.

1. In the conclusion and discussion part, please discuss the social, economic, and environmental impacts of highway PPPs more thoroughly.

2. Please clearly outline potential areas for future research and offer implications for subsequent studies in this field.

 

 

Comments on the Quality of English Language

There are minor instances of awkward phrasing or word choice, but these do not significantly detract from the overall quality of the manuscript.

1. In the abstract, the phrase "the evolution of approaches and prospects in road infrastructure projects" could be rephrased for clarity. A more straightforward phrasing might be "approaches to and prospects for the evolution of road infrastructure projects."

 

1.  
2.  

Author Response

Dear reviewer, we would like to express our appreciation for the recommendations provided to improve the original version of the manuscript. We have considered each recommendation and made modifications that will contribute to meeting your recommendations and improve the quality of the manuscript for future readers, should it eventually be deemed suitable for publication.

 Below, we present an organisation of the different recommendations you have provided us with, together with our corresponding responses. Where modifications to the manuscript have been required, these are in red.

Question 1.  In the methods part, the authors may think of providing more detailed explanations of the bibliometric methods. Please explain the benefit of using the VOSViewer software.

ANSWER 1. This comment is very valuable. In the initial version of the manuscript, the authors did not indicate the bibliometric references supporting using the VOSViewer software in the methods section. However, in the new version of the manuscript, we have incorporated the references supporting the advantages of using the VOSViewer software.

Question 2. In the conclusion and discussion part, please discuss the social, economic, and environmental impacts of highway PPPs more thoroughly.

ANSWER 2. The recommendation is very appropriate. In the new version of the manuscript, we have incorporated Table 13, where we have consigned the future lines of research of the four clusters identified in the keyword network.

Please, if, after the above explanation, the we authors cannot respond to your recommendation, we would be grateful if you could help us improve this aspect in a second round of review.

Question 3. Please clearly outline potential areas for future research and offer implications for subsequent studies in this field.

ANSWER 3. Again, we appreciate the comment. It is similar to recommendation 2. Again, we appreciate the comment. It is similar to recommendation 2. In the new version of the manuscript, we, the authors, have included Table 13, in which the future lines of research of the four clusters representing the main research topics addressed in the research line on PPPs are listed.

Question 4. There are minor instances of awkward phrasing or word choice, but these do not significantly detract from the overall quality of the manuscript.

ANSWER 4. The recommendation is very appropriate. We would like to report that we have corrected the typographical error in the new version of the manuscript.

Question 5. In the abstract, the phrase "the evolution of approaches and prospects in road infrastructure projects" could be rephrased for clarity. A more straightforward phrasing might be "approaches to and prospects for the evolution of road infrastructure projects."

ANSWER 5. The authors appreciate this recommendation and share your concern, so we have rewritten the abstract to give more clarity in the new version of the manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

This is an interesting review article on public-private partnership (PPP) in road construction

. The following are some aspects that need attention:

·        The title of the study should indicate “review”.

·        There is a need for consistency in using terms like ‘highway’ or ‘road infrastructure’. However, what are the relevant terms used in this context and why did the authors select the specific term?

·        Authors need to justify the need for the current review. In Google Scholar search ("Review" AND "bibliometric analysis" AND "Road infrastructure" OR "Highway" OR "road construction" AND "public-private partnership" OR "PPP"). Most of the notable review studies were ignored. What was lacking in previous reviews which have been addressed in the current review?

·        Most importantly the selection of the articles is not systematic as it seems articles related to other disciplines are included in this review. This questions the conduct of the review.

 

·        The co-occurrence of the keywords and network are generic and there is no clarity on the overall outcome of the study. The findings are obvious as most of the research trends were already highlighted in previous review studies. It is very difficult to understand the theoretical contribution of the study. 

Author Response

Dear reviewer, we would like to express our appreciation for the recommendations made to the original version of the manuscript. We have meticulously addressed each suggestion, incorporating modifications to comply with your indications and improve the quality of the manuscript for future readers, should it be deemed appropriate for publication.

Below, the authors we have organized the different recommendations that have been proposed to us, as well as providing a response to each of them. In case modifications have been required in the manuscript, these are indicated in red.

Question 1. The title of the study should indicate “review”.

ANSWER 1. The authors are grateful for this recommendation. We want to inform you that we have incorporated the change in the title.

Question 2. There is a need for consistency in using terms like ‘highway’ or ‘road infrastructure’. However, what are the relevant terms used in this context and why did the authors select the specific term?

ANSWER 2. The recommendation is very appropriate. We would like to report that we have corrected the typographical error in the new version of the manuscript.

Question 3.  Authors need to justify the need for the current review. In Google Scholar search ("Review" AND "bibliometric analysis" AND "Road infrastructure" OR "Highway" OR "road construction" AND "public-private partnership" OR "PPP"). Most of the notable review studies were ignored. What was lacking in previous reviews which have been addressed in the current review?

ANSWER 3.  Thank you for your comment. The we authors have reviewed databases such as Web of Science, Google Scholar and Scopus. However, we would like to report that we have selected the Scopus database for the following reasons: (a) it is the database with the largest volume of information on authors, institutions and countries (Zhang & Eichmann-Kalwara, 2019) ; (b) it is the repository with the largest number of articles and reviews that meet the quality requirements of peer review (Ackerson & Chapman, 2003; Mingers & Lipitakis, 2010) and (c) it has the largest coverage (Archambault et al., 2009). However, Google Scholar does not meet the quality requirements we have justified in the methodology.

Question 3.1. What was lacking in previous reviews which have been addressed in the current review? ¿Qué carencias de las revisiones anteriores se han abordado en la actual?

ANSWER 3.1. The authors are grateful for this recommendation. We would like to report that we have expanded the academic literature in this section of the paper, trying to widen the research gap and explain what the main contributions of our research are to the previous academic literature.

Question 4. Most importantly the selection of the articles is not systematic as it seems articles related to other disciplines are included in this review. This questions the conduct of the review.

ANSWER 4. We are grateful for your recommendation. We want to point out that, as explained in the methodology section, our manuscript is not a systematic review but a bibliometric review whose main objective is to analyse the entire academic production in the research line on PPPs in road infrastructure projects. In that context, we aim to assess the leading bibliometric indicators and the most salient developments that have occurred in general terms within the research line.

Question 5. The co-occurrence of the keywords and network are generic and there is no clarity on the overall outcome of the study. The findings are obvious as most of the research trends were already highlighted in previous review studies. It is very difficult to understand the theoretical contribution of the study.

ANSWER 5. Thank you for your comment. The authors would like to explain that through the keyword analysis, we have identified the main topics addressed in the line of research. With the grouping of the keywords in clusters, we analysed each research topic, identifying the main contributions. Likewise, the research trends show the temporal evolution of the line of research and the different topics that comprise it. On the one hand, the darker colours show the keywords that contributed at the beginning of the research line, while the lighter colours show the current research trends.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors significantly addressed the reviewer's comments. However, there is a need to enhance the discussion on future research with the explanation of potential research opportunities. The authors need to compare the current findings with similar research to signify their work. PPP research is contextualized by type of project, contract and country dynamics. 

Author Response

Dear reviewer, the authors would like to thank you for the recommendations made to the original version of the manuscript. The recommendations have been very precise, so the authors have incorporated modifications that we hope will help to comply with these recommendations and contribute to improving the quality of the manuscript for future readers if it is ultimately suitable for publication.

Below, the authors we have organized the different recommendations that have been proposed to us, as well as providing a response to each of them. In case modifications have been required in the manuscript, these are indicated in red.

Question 1. The authors significantly addressed the reviewer's comments. However, there is a need to enhance the discussion on future research with the explanation of potential research opportunities. The authors need to compare the current findings with similar research to signify their work. PPP research is contextualized by type of project, contract and country dynamics. 

ANSWER 1. The authors are grateful for this recommendation. The we authors agree to extend the future lines of research and conclusions. Therefore, we have improved the discussion of future lines of research at the end of section 5. On the other hand, we have expanded section 6 by stating the novelty of our research concerning previous academic literature.