From Simulation to Implementation: A Systems Model for Electric Bus Fleet Deployment in Metropolitan Areas

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I think the authors did a good job, however, I still have some concerns:

1. I feel that section 2 is not positioned in a right place, I suggest to move this section to somewhere else.
2. In section 3, I suggestion to discuss or introduce the situation in China as the EV inductry develops rapidly in China.
3. There is no step 6 in Figure 1.

Author Response

Dear Reviewer 1,

thank you for your helpful review. We have taken your comments into account:

Comment 1: I feel that section 2 is not positioned in a right place, I suggest to move this section to somewhere else.

Response 1: We have changed the structure of the paper, expanded section 2 and moved it into the introduction.

Comment 2: In section 3, I suggestion to discuss or introduce the situation in China as the EV inductry develops rapidly in China.

Response 2: We have added a paragraph on the Chinese Electric bus deployment in the introduction.

Comment 3: There is no step 6 in Figure 1.

Response 3: Figure 1 has been split up into two figures (1 and 2) and significantly reworked. We believe it is more consistent now.

Reviewer 2 Report

Comments and Suggestions for Authors

This paper presents a comprehensive, modular simulation framework—“eflips-X”—for electrifying urban bus networks, validated with a case study on Berlin’s bus system. The contribution is highly relevant given the increasing urgency of decarbonizing public transport systems.

The manuscript is well-structured and clearly written, with sufficient methodological detail and sound justification for the selected approaches. The use of open-source tools and reproducible methodologies is particularly commendable.

 

The authors explicitly exclude TCO (Total Cost of Ownership) and environmental impact assessments. Including even basic estimates (or sensitivity analyses) would broaden applicability for policy decision-making.

 

Grid capacity and interactions are only indirectly addressed. Integration with real-time grid data or co-simulation with energy management systems would enhance robustness.

 

While the technical depth is impressive, the usability for planners with limited programming experience may be limited. The authors may consider outlining how future work could improve accessibility, such as through GUI development or integration with planning dashboards.

 

The framework’s runtime is reported for the Berlin dataset, but further performance benchmarks (e.g., for smaller or denser networks) would help potential users assess applicability to other settings.

 

Attempt to increase the literature review focused on electric mobility. We recommend including the following reference. https://doi.org/10.3390/wevj15120583

 

Improve consistency in terminology (e.g., “block,” “vehicle schedule,” “trip sequence”).

Author Response

Dear Reviewer 2,

thank you for your helpful review. We have tried to take it into account directly, however while all proposed changes would improve the quality of this publication, they are not all feasible.

Comment 1: Including even basic [economic] estimates (or sensitivity analyses) would broaden applicability for policy decision-making.

Response 1: We agree with the importance of TCO, especially if combined with a "life cycle assessment" approach. However, we feel this paper is internally consistent in its focus on operations. We have expanded our outlook to include a more detailed discussion of future economic assessments.

Comment 2: Integration with real-time grid data or co-simulation with energy management systems would enhance robustness.

Response 2: This comment highlights an interesting future research direction. It has been reflected in the outlook.

Comment 3: The authors may consider outlining how future work could improve accessibility, such as through GUI development or integration with planning dashboards.

Response 3: Work on a GUI is already in progress (however no citeable publications yet, there has only been a Poster by Moritz Schiel at EVS 38 in Göteborg). This was referenced in the outlook.

Comment 4: but further performance benchmarks (e.g., for smaller or denser networks)

Response 4: Including other networks would be great, but there is a significant difficulty in finding bus operators willing to share their detailed operational data. As such, it cannot be done in this publication. 

Comment 5: We recommend including the following reference. https://doi.org/10.3390/wevj15120583

Response 5: In our opinion, this paper focuses on the state of deployment and incentives, while our current work focuses on simulation methods. However, we are grateful for the suggestion as we are planning future work on EV deployments in Brazil.

Comment 5: Improve consistency in terminology (e.g., “block,” “vehicle schedule,” “trip sequence”).

Response 5: We have done one more pass and fixed this in some tables. While the word "vehicle schedule" remains present at some points, it is only in definitions of the term.

Reviewer 3 Report

Comments and Suggestions for Authors

Comments are attached in the report

Comments for author File: Comments.pdf

Author Response

Dear Reviewer 3,

thank you for your helpful review. We have taken it into account in our revised paper.

Comment 1: The first portion of the article structure is a bit odd and concise thesis or dissertation rather than a journal article. The introduction and background sections could be more focused, with a clearer statement of the paper’s objective toward the end of the introduction.

Response 1: The first portion has been substantially reworked, with a statement of the scientific contribution of this publication added.

Comment 2: For the terminus charger placement, SBT requires 64 electrified termini versus 44 in EBU, despite nearly all vehicles needing terminus charging. Charger utilization and queuing are not analyzed. The 10-minute break rule will need some justification or assumption. The author should also discuss some model limitations based on model assumptions and related future work to improve the model.

Response 2: As shown in Figure 14 and Table 15, even though there are only 20 more termini, the peak utilization (and the number of charging points needed per terminus) increases significantly. Regarding the 10-minute break, we have justified the assumption -- it was based on our observed battery depletion. Regarding future work, we have expanded the outlook and made it its own subsection.

Comment 3: There is a missing citation in Table 1 for the 2021 entry, currently marked with a “?”

Response 4: Has been fixed, thanks!

Comment 4: In Section 4.2.1, many words appear in italics without a clear pattern or explanation. Were those words supposed to be a typo?

Response 4: The technical terms from graph theory are highlighted in italics. I will bring this to the attention of the editor and ask them to make a decision based on the style guidelines of this journal.

Reviewer 4 Report

Comments and Suggestions for Authors

The authors tackle an interesting and modern subject, which is electric bus fleets in metropolitan areas. However, certain issues need to be addressed:

1) The abstract is too brief.

2) Sections 1-3 could be one Introduction. 

3) At the end of the Introduction, the scientific contribution of the manuscript should be highlighted.

4) The architecture of Fig. 1 is too complex.

5) The methodology has no mathematical background, which is not suitable for a journal publication. All formulas are in the Appendix and should be moved appropriately. 

6) When shifting from one form of transport (conventional) to another (electric), it is critical to calculate the Net Present Value (NPV) and other investment-related indicators.

7) Indeed, the electric vehicles / buses affect the power system and can be scheduled as flexible loads. The authors need to discuss more about this and are encouraged to enhance their literature analysis with recent, relevant articles, such as, for example:

https://doi.org/10.3390/en18051101

https://doi.org/10.3390/wevj13110212

Taking the aforementioned comments into consideration, a major revision of the manuscript is proposed.

Author Response

Dear Reviewer 4,

Thank you for the feedback. We have revised our publication quite substantially based on it. 

Comment 1: The abstract is too brief.

Response 1: The abstract has been re-written and extended based on journal guidelines. I somehow thought the word limit was lower than it actually was…

Comment 2: Sections 1-3 could be one Introduction. 

Response 2: You are right. Done and slightly cleaned up the reading flow.

Comment 3:  At the end of the Introduction, the scientific contribution of the manuscript should be highlighted.

Response 3: We have added this section. Due to the length of our literature review, we have chosen to not place it at the end of the introduction, though.

Comment 4: The architecture of Fig. 1 is too complex.

Response 4: Figure 1 has been split into two figures, with some of its information instead presented as Tables in (post-revision) Section 2. We believe this significantly increases clarity.

Comment 5: The methodology has no mathematical background, which is not suitable for a journal publication. All formulas are in the Appendix and should be moved appropriately. 

Response 5: Only two of our parts (depot-block assignment and smart charging) use ILPs that are expressed mathematically. For other parts we use graph theory (which we explain using figures) and reference existing algorithms or heuristics. We believe the paper flows better if it has the relevant formulas in the appendix instead of suddenly having two blocks of heavy math in an otherwise "math-light" publication. We will bring this question to the attention of the editor and are open to moving the formulas into the main body if it is required.

Comment 6: When shifting from one form of transport (conventional) to another (electric), it is critical to calculate the Net Present Value (NPV) and other investment-related indicators.

Response 6: We share your view about the importance of economic indicators and have expanded its position in the outlook. However, as economic analysis must always build upon the operational results and generating them is already quite complex, we would like to maintain the focus on operational results in this publication.

Comment 7: Indeed, the electric vehicles / buses affect the power system and can be scheduled as flexible loads. The authors need to discuss more about this and are encouraged to enhance their literature analysis with recent, relevant articles, such as, for example:

https://doi.org/10.3390/en18051101

https://doi.org/10.3390/wevj13110212

Response 7: We also think that considering flexible loads in charging process is necessary and thus now include a section reviewing smart charging strategies in electric bus networks. However, since the recommended papers focused more on energy communities or electric network planning in general, we prefer literature addressing the specific problem of smart charging strategies in battery electric bus systems. Furthermore, we have added a section on potential grid co-simulation to the outlook.

 

Reviewer 5 Report

Comments and Suggestions for Authors

The authors of the paper 'From Simulation to Implementation: A Systems Model for Electric Bus Fleet Deployment in Metropolitan Areas' have presented a contemporary and highly relevant study that deals with the comprehensive integration of electric buses into public transport systems using the city of Berlin as a case study. The study's primary strength lies in the development and application of an integrated, modular simulation framework that connects all essential aspects of electrification planning, including block formation, depot assignment, charger placement, and charging optimisation. Previous literature has mostly considered these aspects in isolation.

The paper contains a large amount of data and provides a comprehensive overview of the entire process, which is certainly a strength as it gives readers a thorough understanding of the topic. However, such an extensive approach, with numerous details and procedural steps, partially dilutes the scientific precision of the work and gives it a more educational than research-oriented character. Therefore, it would be useful for the authors to clearly explain in the Introduction why the integrated presentation of all these elements in one place is important and what constitutes its added scientific value.

As the main strength of this paper lies in the integration of all procedures related to the electrification of public bus transport, as summarised in Figure 1, it would be useful for the authors to specify and explain more precisely which concrete input data each module uses, including model parameters and data provided by the bus operator, as well as the outputs of individual simulation steps. Presenting this information in a table would enhance transparency and facilitate the reproducibility of the presented model. It is particularly important to clearly define the minimum data requirements necessary to apply the model in other contexts, as this aspect is not addressed in the current version of the paper.

In Chapter 6, 'Discussion', the authors comment on their own findings. However, a quantitative comparison between the integrated model and the modular (disconnected) approaches from previous research is lacking. Within each subsection of 6.1 Key Findings and Implications (e.g. Energy Consumption and Temperature Effects, Block Building and Scheduling, etc.), it would be beneficial if the authors systematically compared their results with relevant findings from the literature. This would strengthen the discussion further, providing a clearer assessment of the paper's contribution relative to existing studies and helping readers to better understand the advantages and limitations of the proposed integrated model.

Technical notes and suggestions for corrections:

• Figure 1: The algorithm diagram is not entirely accurate. The feedback loop with the decision-making step is not clearly defined as the word 'no' is shown as entering the decision node itself, which may cause confusion when interpreting the process flow.
• Lines 437, 452 and 571: The text lacks appropriate references, which should be added.

Author Response

Dear Reviewer 5,

Thank you for your helpful feedback. 

Comment 1: Therefore, it would be useful for the authors to clearly explain in the Introduction why the integrated presentation of all these elements in one place is important and what constitutes its added scientific value.

Response 1: In retrospect, this was definitely needed. It has been added. (section 1.2)

Comment 2: […] specify and explain more precisely which concrete input data each module uses, including model parameters and data provided by the bus operator, as well as the outputs of individual simulation steps […]

Response 2: We have reworked how we present this. We have simplified and broken up figure 1 into figures 1 and 2, while also adding tables to the beginning of each subsection of (now) Section 2 specifying the inputs and outputs. We appreciate the comment and hope this makes it easier to understand.

Comment 3: […] it would be beneficial if the authors systematically compared their results with relevant findings from the literature […]

Response 3: We emphatically agree with this comment, but sadly are not able to implement it. As discussed in our Introduction, the existing publication landscape differs in both methods and datasets, with both not being made available. Therefore, comparisons to existing literature have a significant risk of being ``apples and oranges'' comparisons, showing difference in results but not able to differentiate between ones caused by the underlying bus network or
 the approaches by the researchers. We hope our open source and open data approach can contribute to reducing this problem in the future.

Comment 4: Technical notes

Response 4: Thanks, done

Round 2

Reviewer 4 Report

Comments and Suggestions for Authors

The authors have not addressed the following previous comments:

Comment 5: The methodology has no mathematical background, which is not suitable for a journal publication. All formulas are in the Appendix and should be moved appropriately.

Comment 6: When shifting from one form of transport (conventional) to another (electric), it is critical to calculate the Net Present Value (NPV) and other investment-related indicators.

Comment 7: Indeed, the electric vehicles / buses affect the power system and can be scheduled as flexible loads. The authors need to discuss more about this and are encouraged to enhance their literature analysis with recent, relevant articles, such as, for example:

https://doi.org/10.3390/en18051101

https://doi.org/10.3390/wevj13110212

Author Response

Dear Reviewer 4,

Thanks again for your valuable comments. As proposed, we have moved all formulas into the main body of the article. The proposed literature was incorporated where appropriate. We agree that Net Present Value is of particular importance, however our article focuses on the technical and operational aspects. We provide a sound basis for future NPV analyses of different system alternatives. Since we go into many details which have not been addressed before, the paper is comprehensive and extensive. An economic analysis is already underway and going to be published in a subsequent paper.

 

Kind Regards,

Ludger Heide

Reviewer 5 Report

Comments and Suggestions for Authors

Dear,

I have reviewed the revised manuscript and the authors’ responses to the comments. I can confirm that all the suggested corrections have been appropriately addressed, and that the manuscript has been revised in accordance with the review.

Therefore, I recommend that the paper be accepted for publication.

Author Response

Dear Reviewer 5,

thanks for the go-ahead and thank you again for your valuable feedback!

Kind Regards

Ludger Heide

Round 3

Reviewer 4 Report

Comments and Suggestions for Authors

Thank you for addressing the comments.