Review Reports - Transitioning to Hydrogen Trucks in Small Economies: Policy, Infrastructure, and Innovation Dynamics

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript ‘Transitioning to Hydrogen Trucks in Small Economies: Policy, Infrastructure, and Innovation Dynamics’ is a well-structured and timely contribution that advances understanding of hydrogen-truck transitions in small economies. Its integration of system-dynamics modeling with qualitative policy insights is a clear strength. However, further improvements are needed before acceptance; accordingly, I recommend major revisions, as detailed below.

The authors should add a clear research gap statement at the end of the Introduction, specifying how this model differs (e.g., inclusion of industrial hydrogen demand linkages, policy elasticity, or small-market constraints).
The model is detailed but lacks discussion of validation. Include a brief validation or sensitivity analysis section (even qualitative) to show parameter reliability and strengthen credibility.
Include a brief paragraph in Discussion or Conclusion comparing potential transferability would strengthen the paper’s generalizability.
Figures 1–9 convey the logic well but are visually dense. Consider streamlining and grouping the sub-models, with thematic color-coding and a compact legend.
The conclusions are strong but could be improved by adding clear future research directions, such as cross-country comparisons and inclusion of life-cycle or supply-chain factors.
The writing is generally clear and well-structured, though some parts particularly in the Abstract and Introduction could be more concise to improve clarity and impact.

Author Response

We sincerely thank you for your feedback and recommendations! We greatly appreciate your contribution and support in publishing our article. We have reviewed your recommendations and are ready to provide our responses and corrections.

Comment 1: The authors should add a clear research gap statement at the end of the Introduction, specifying how this model differs (e.g., inclusion of industrial hydrogen demand linkages, policy elasticity, or small-market constraints).

Response 1: Thank you for this recommendation – it is noted. We had completed introduction part by adding 2 paragraphs in the end of the chapter specifying research gaps addressed in our manuscript. Also, we have defined how proposed model differ from already existing solutions.

Comment 2: The model is detailed but lacks discussion of validation. Include a brief validation or sensitivity analysis section (even qualitative) to show parameter reliability and strengthen credibility.

Response 2: This recommendation is fully accepted, therefore, we have improved manuscript by adding new subchapter 4.4. Sensitivity analysis, where results are discussed and validated, as well as sensitivity charts are displayed.

Comment 3: Include a brief paragraph in Discussion or Conclusion comparing potential transferability would strengthen the paper’s generalizability.

Response 3: Fully noted – conclusions have been improved by adding two additional paragraphs in the end of the chapter highlighting transferability and potential future research areas.

Comment 4: Figures 1–9 convey the logic well but are visually dense. Consider streamlining and grouping the sub-models, with thematic color-coding and a compact legend.

Response 4: Thank you for this valuable recommendation. We tried to display logic of the model in a simple and visually attractive style. Please be assured that in the manuscript we have already included consolidated and simplified version of the model. According to systems dynamic method, models are often complex and contain multiple variables necessary for forecasting. We have tried to eliminate useless and non-essential parts to better represent our idea in the manuscript. Therefore, to sustain integrity and quality of the paper, we would prefer to use previously included figures, However, we have slightly improved casual loop diagram by naming balancing and reinforcing loops. We also do believe that after editorial changes and formatting of the text, our figures will be more visually attractive.

Comment 5: The conclusions are strong but could be improved by adding clear future research directions, such as cross-country comparisons and inclusion of life-cycle or supply-chain factors.

Response 5: Fully noted – conclusions have been improved by adding two additional paragraphs in the end of the chapter highlighting transferability and potential future research areas.

Comment 6: The writing is generally clear and well-structured, though some parts particularly in the Abstract and Introduction could be more concise to improve clarity and impact.

Response 6: We have made some improvements to the abstract to better highlight structure of the manuscript, aim, novelty and

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript discuss an important topic on hydrogen trucks in small economies. The approach is promising, but the analysis and presentation need more clarity and stronger data support. Here are few points needs to be considered:

1- (Page 3, L1–31): Clearly define how the proposed system dynamics model differs from existing hydrogen transition studies and specify the main research questions guiding the analysis.

2- (Page 27, L22–87; Page 30, L40–64).: Present equations, input data, and validation or sensitivity analysis. Include units and references in all tables to ensure reproducibility and scientific rigor.

3- (Throughout; Page 19, L19–35; Page 27, L22–35): Replot all figures for readability, remove formatting artifacts and add captions to the tables

Author Response

Comment 1: (Page 3, L1–31): Clearly define how the proposed system dynamics model differs from existing hydrogen transition studies and specify the main research questions guiding the analysis.

Response 1: Thank you for this recommendation – it is fully noted. We have improved this part of the manuscript by defining how proposed system dynamics model differs from existing hydrogen transition studies - by explicitly incorporating small-market constraints, cross-sectoral hydrogen demand interactions, and policy elasticity effects often absent in large-market analyses.

Comment 2: (Page 27, L22–87; Page 30, L40–64).: Present equations, input data, and validation or sensitivity analysis. Include units and references in all tables to ensure reproducibility and scientific rigor.

Comment 3: Throughout; Page 19, L19–35; Page 27, L22–35): Replot all figures for readability, remove formatting artifacts and add captions to the tables

Response 3: Thank you for this valuable recommendation. We tried to display logic of the model in a simple and visually attractive style. Please be assured that in the manuscript we have already included consolidated and simplified version of the model. According to systems dynamic method, models are often complex and contain multiple variables necessary for forecasting. We have tried to eliminate useless and non-essential parts to better represent our idea in the manuscript. Therefore, to sustain integrity and quality of the paper, we would prefer to use previously included figures. However, we have slightly improved casual loop diagram by naming balancing and reinforcing loops. We also do believe that after editorial changes and formatting of the text, our figures will be more visually attractive.

Reviewer 3 Report

Comments and Suggestions for Authors

Improve English.
Justify the abstract.
Authors should improve the abstarct and conclusion.
Conclusion should have some future recommendation researches.
Put a table to compare the previous publish works with yours.
There are some similar works, what is the novelty of your manuscript?
How does the evolution of industrial hydrogen demand influence the cost-effectiveness of hydrogen trucks in small economies, and what role does international demand play in this dynamic?
To what extent do variations in acquisition, maintenance, and fuel cost weights affect fleet operators’ decisions when transitioning to BEV or H2 trucks under different market scenarios?
Introduction and literature review should be improved a lot. Authors must cite the below references:

Jiang, C., Wang, Y., Yang, Z., & Zhao, Y. (2023). Do adaptive policy adjustments deliver ecosystem-agriculture-economy co-benefits in land degradation neutrality efforts? Evidence from southeast coast of China. Environmental Monitoring and Assessment, 195(10), 1215. doi: 10.1007/s10661-023-11821-6
Dou, Z., Ye, Z., Zhang, C., & Liu, H. (2025). Development and process simulation of a biomass driven SOFC-based electricity and ammonia production plant using green hydrogen; AI-based machine learning-assisted tri-objective optimization. International Journal of Hydrogen Energy, 133, 440-457. doi: https://doi.org/10.1016/j.ijhydene.2025.04.497
http://sciencedirect.com/science/article/pii/S2772427125000932
Meng, Q., Zu, G., Ge, L., Li, S., Xu, L., Wang, R.,... Jin, S. (2022). Dispatching Strategy for Low-Carbon Flexible Operation of Park-Level Integrated Energy System. Applied Sciences, 12(23), 12309. doi: 10.3390/app122312309
Song, M., Zhang, Y., Li, M., & Zhang, Y. (2021). Accessibility of Transit Stops with Multiple Feeder Modes: Walking and Private-Bike Cycling. Sustainability, 13(6), 3522. doi: 10.3390/su13063522
https://link.springer.com/article/10.1007/s41939-024-00482-8

Author Response

Comment 1: Improve English.

Response 1: Thank you for this recommendation! Proof reading has been conducted for entire manuscript and English has been improved.

Comment 2: Justify the abstract.

Response 2: We have made some improvements to the abstract to better highlight structure of the manuscript, aim, novelty and other important elements of the research. That you for this recommendation, it is noted!

Comment 3: Authors should improve the abstarct and conclusion.

Response 3: We have made improvements to the abstract to better highlight structure of the manuscript. Conclusions have been improved by adding two additional paragraphs in the end of the chapter highlighting transferability and potential future research areas.

Comment 4: Conclusion should have some future recommendation researches.

Response 4: Conclusions have been improved by adding two additional paragraphs in the end of the chapter highlighting transferability and potential future research areas.

Comment 5: Put a table to compare the previous publish works with yours.

Response 5: Thank you for the suggestion. A dedicated comparison table was considered; however, the manuscript already includes a structured comparison between prior studies and the present model. This is explicitly addressed in the end of Introduction (we have added 2 paragraphs), where we highlight how our system-dynamics approach differs from existing hydrogen transition studies, particularly regarding small-market constraints, cross-sectoral demand integration, and policy elasticity. Therefore, an additional table would not add further value.

Comment 6: There are some similar works, what is the novelty of your manuscript?

Response 6: Thank you for this question! As it was highlighted in the manuscript, the study introduces a system dynamics model specifically tailored to the structural constraints of small economies, integrating industrial hydrogen demand, policy elasticity, and infrastructure coverage limitations - factors largely omitted in previous hydrogen transition studies. Unlike existing models focused on large markets or single-sector adoption, our approach captures cross-sector synergies, small-scale cost dynamics, and subsidy-driven tipping points, providing a uniquely realistic framework for hydrogen truck deployment in small-country contexts.

Comment 7: How does the evolution of industrial hydrogen demand influence the cost-effectiveness of hydrogen trucks in small economies, and what role does international demand play in this dynamic?

Response 7: In the model, domestic industrial hydrogen demand is a key driver of cost reduction through economies of scale. Because small economies cannot rely on transport demand alone, the inclusion of industrial demand, reflecting planned local hydrogen production, helps lower fuel costs and improve the cost-effectiveness of hydrogen trucks. Although the model incorporates only domestic demand, international hydrogen demand remains an important external factor: global market growth accelerates technological learning and supply-chain efficiencies, indirectly reducing costs. Thus, strong industrial uptake at home, supported by broader international trends, is essential for hydrogen truck viability in small-country contexts.

Comment 8: To what extent do variations in acquisition, maintenance, and fuel cost weights affect fleet operators’ decisions when transitioning to BEV or H2 trucks under different market scenarios?

Response 8: In the model, the weights for acquisition, maintenance, and fuel costs directly shape the general attractiveness indices and thus the allocation of renewal demand between ICE, BEV, and H2 trucks. Under all scenarios, higher acquisition cost weight tends to favor BEV, while a higher fuel-cost weight increases the relative attractiveness of H2 in high-mileage use. In small economies, where total renewal volumes are limited, even moderate changes in these weights can produce disproportionate shifts in fleet composition, especially in the Balanced and H2-favorable scenarios, whereas the Market-led scenario remains dominated by BEV due to weaker policy support.

The model is intentionally designed to allow adjusting these proportions, enabling exploration of a wide range of behavioral assumptions and transition pathways.

Comment 9: Introduction and literature review should be improved a lot. Authors must cite the below references:

Response 9: Thank you for this recommendation! We had completed introduction part by adding 2 paragraphs in the end of the chapter specifying research gaps addressed in our manuscript. Also, we have defined how proposed model differ from already existing solutions. According to your suggested list of articles, we found it useful to integrate and cite work of Soleimani et al.(2024) that, according to our point of view, well corresponds to the theme of our research!

Reviewer 4 Report

Comments and Suggestions for Authors

General Critique and Structural Recommendations

The overall manuscript is quite long, but it fails to specify the novel contribution of the System Dynamics model provided. Furthermore, pages 23–27 contain a significant number of editorial marks/track changes that need resolving.

Recommendations:

Length Reduction: I recommend compressing the manuscript length by 50%.
Pre-Submission Review: Prior to submission, meticulously and repeatedly check the entire manuscript, including all cited literature and references, for accuracy and consistency.

Specific Feedback on Model and References

Here are several specific suggestions regarding the figures and references:

Item	Suggestion
Fig. 1	It is highly recommended to label and number the feedback loops in the Causal Loop Diagram (CLD) to facilitate their sequential introduction and discussion in the text.
Fig. 2-5	I suggest merging these individual diagrams into one complete Stock-and-Flow Diagram (SFD) for better overall clarity and comprehension of the model structure.
Fig. 5	Please clarify the modeling logic: Why is only ICE Disposal counted into the Fleet for Renewal?
References	The following references are wrong or non-existing and require immediate correction or replacement: #42, #43, #44, #54.

Author Response

Comment 1: The overall manuscript is quite long, but it fails to specify the novel contribution of the System Dynamics model provided. Furthermore, pages 23–27 contain a significant number of editorial marks/track changes that need resolving.

Response 1: Thank you for evaluating our manuscript. We have conducted a full review of the entire text – improved style, writing and English proof reading. There are various improvements of using terms, statements. Therefore, we hope this improved version of the manuscript better specify novel contribution of system dynamics. We had completed introduction part by adding 2 paragraphs in the end of the chapter specifying research gaps addressed in our manuscript. Also, we have defined how proposed model differ from already existing solutions.

Comment 2: Length Reduction: I recommend compressing the manuscript length by 50%.

Response 2: Thank you for this recommendation! A 50% length reduction is not feasible, unfortunately, without compromising the scientific integrity of the manuscript. First, the system dynamics model relies on transparent documentation of structures, assumptions, and parameters, so substantial shortening would reduce reproducibility. Second, the comparison of three policy scenarios requires detailed explanation to ensure interpretability and policy relevance, especially for small-economy contexts. Third, other requested additions, such as research gap clarification, model differentiation, and sensitivity analysis, have already expanded critical sections. Further compression would weaken clarity, methodological transparency, and overall contribution.

Comment 3: Pre-Submission Review: Prior to submission, meticulously and repeatedly check the entire manuscript, including all cited literature and references, for accuracy and consistenc

Response 3: We have conducted a full review of the entire text – improved style, writing and English proof reading. Also, we have carefully examined and corrected all the errors in cited literature and references. You may find updated manuscript with all corrections enclosed.

Comment 4: It is highly recommended to label and number the feedback loops in the Causal Loop Diagram (CLD) to facilitate their sequential introduction and discussion in the text.

Response 4: Thank you, this recommendation is fully noted. We have modified CLD by indicating and naming feedback loops. Also, there references are further used in the text of the manuscript.

Comment 5: I suggest merging these individual diagrams into one complete Stock-and-Flow Diagram (SFD) for better overall clarity and comprehension of the model structure.

Response 5: A single merged SFD would significantly reduce readability, as the full model contains multiple interacting sub-systems with high visual density. Presenting the stock-and-flow structure in separate diagrams improves clarity, allows readers to understand each conceptual block independently, and aligns with best practices in system dynamics for communicating complex multi-sector models.

Please be assured that in the manuscript we have already included consolidated and simplified version of the model. According to systems dynamic method, models are often complex and contain multiple variables necessary for forecasting. We have tried to eliminate useless and non-essential parts to better represent our idea in the manuscript. Therefore, to sustain integrity and quality of the paper, we would prefer to use previously included figures.

Comment 6: Please clarify the modeling logic: Why is only ICE Disposal counted into the Fleet for Renewal?

Response 6: In the current model design, Fleet for renewal represents the replacement demand generated by the gradual phase-out of the legacy ICE fleet, which dominates the starting vehicle stock in a small economy. Only ICE Disposal is counted because the transition process is driven primarily by retiring ICE trucks and reallocating this renewal demand between ICE, BEV, and H2 according to their evolving attractiveness. BEV and H2 trucks (technology) are assumed to remain in service over the simulation horizon. Fleet growth beyond replacement is modeled separately via an exogenous growth rate and then allocated across technologies, so including BEV/H2 disposal would add complexity without materially changing the transition dynamics.

Comment 7: The following references are wrong or non-existing and require immediate correction or replacement: #42, #43, #44, #54.

Response 7: Thank you, we have carefully examined and corrected all the errors in cited literature and references.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Author Response

Comment: Accepted.

Response: Good afternoon! Thank you for accepting our manuscript. Your recommendations are highly appreciated and considered, and we are happy to submit final version of the manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

Authors should cite the below references:

Jiang, C., Wang, Y., Yang, Z., & Zhao, Y. (2023). Do adaptive policy adjustments deliver ecosystem-agriculture-economy co-benefits in land degradation neutrality efforts? Evidence from southeast coast of China. Environmental Monitoring and Assessment, 195(10), 1215. doi: 10.1007/s10661-023-11821-6
Dou, Z., Ye, Z., Zhang, C., & Liu, H. (2025). Development and process simulation of a biomass driven SOFC-based electricity and ammonia production plant using green hydrogen; AI-based machine learning-assisted tri-objective optimization. International Journal of Hydrogen Energy, 133, 440-457. doi: https://doi.org/10.1016/j.ijhydene.2025.04.497
Meng, Q., Zu, G., Ge, L., Li, S., Xu, L., Wang, R.,... Jin, S. (2022). Dispatching Strategy for Low-Carbon Flexible Operation of Park-Level Integrated Energy System. Applied Sciences, 12(23), 12309. doi: 10.3390/app122312309
Song, M., Zhang, Y., Li, M., & Zhang, Y. (2021). Accessibility of Transit Stops with Multiple Feeder Modes: Walking and Private-Bike Cycling. Sustainability, 13(6), 3522. doi: 10.3390/su13063522

Author Response

Comment: Authors should cite the below references

Response: Good afternoon! Thank you for providing additional recommendation regarding references. We have updated chapter 2.1 of the manuscript by adding paragraph with references to your suggested articles. It can be found on page 5.