Review Reports - Optimization of the Technical Parameters of Universal Freight Wagons

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper proposes a novel optimization criterion for determining the specific volume and specific area of general-purpose trucks. The traditionally used criterion of “minimum reduced costs” is difficult to apply in practice because the capital and operating costs vary significantly across different regions. Addressing an important practical problem in truck design, this paper introduces a new optimization criterion and validates it using practical case studies. The research methodology is sound, and the structure is clear. However, there are still some areas for improvement in the presentation and expression. It is recommended that the paper be accepted after minor revisions.

1) Although the proposal of the loading self-weight coefficient (Section 2.2.3, Equation (7)) is well-motivated, the paper should more explicitly compare it with other optimization criteria beyond “reduced costs” to highlight its innovation.

2) Figures 3 and 4 (Sections 3.1–3.2.1) are central to the optimization method, but their captions and the corresponding explanations in the text are relatively brief. It is recommended to expand the discussion of intervals I–III in Figure 3, as well as the three cases shown in Figure 4(a–c).

3) It is recommended to cite the following two recent works in the literature review or discussion section to enhance the coverage of background related to “optimization criteria and modern engineering methods” and “lightweighting and advanced manufacturing/thermal management methods”: TITS.2024.3464757 on a real-time global optimization method for vehicle energy management based on traffic flow information, and j.applthermaleng.2024.123984 on the design and manufacturing of multi-U-shaped microchannel cooling plates for battery thermal management.

4) Some of the formula notations are inconsistent or not sufficiently clear (e.g., the summation indices in Equation (20) and Equation (22)). Please standardize the notation and ensure all variables are defined.

5) Section 4 presents numerical results (Table 4) showing a reduction in self-weight and an increase in payload capacity. It is recommended to further discuss the broader implications for railway operators, such as reduced maintenance costs or compatibility with EU TSI standards.

6) There are some minor grammatical issues and formatting inconsistencies in the paper, such as inconsistent spaces in formulas and inconsistent decimal separators in Table 3. It is recommended that a thorough language and formatting revision be conducted.

Author Response

Dear reviewer 1,

Thank you very much for taking the time to review this manuscript. Please find the detailed responses in attached file and the corresponding revisions/corrections highlighted in the re-submitted file.

Best regards

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article addresses an important and interesting topic related to the optimization of technical parameters of universal freight wagons. I appreciate that the authors clearly identify the practical limitations of using the “adjusted costs” criterion and propose an alternative optimization approach based on the loading tare coefficient. The methodology is mathematically consistent and well structured, and the application to the Eamnos wagon type using real operational data adds practical relevance for freight operators and vehicle designers.

However, several revisions are required. The numerical results contain inconsistencies: the reduction of the wagon volume is stated as approximately 8 m³ in the text, while the comparison table indicates a decrease of about 18 m³. Likewise, the load capacity of the optimized wagon differs by about 0.09 t from the value implied by the constant gross weight constraint. These appear to be rounding or editing errors and should be corrected. Additionally, the claim regarding the annual reduction of approximately three wagons per day (or 55 trains per year) is not supported by intermediate calculations, and greater transparency here would improve reproducibility.

I would also like to point out a formatting issue: the numbering of tables is inconsistent, with “Table 2” appearing twice in the manuscript. This should be corrected for clarity.

The optimization was validated using only one wagon type and Bulgarian freight transport data. While the proposed method itself is general and transferable, a brief discussion of how results may vary for other wagon categories or operating conditions would strengthen the manuscript.

Overall, the paper presents a meaningful and useful contribution, and I recommend minor revision, primarily to correct numerical inconsistencies, clarify the economic impact, and address formatting issues.

Author Response

Dear reviewer 2,

Best regards

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This paper makes a valuable contribution by proposing an optimization criterion for the technical parameters of general freight trains based on the "Freight tare coefficient". This criterion addresses the limitations of the existing "adjustment cost" criterion, and the feasibility of the corresponding optimization scheme is verified through a case study, granting the research certain theoretical innovation and practical application potential. That said, there are several aspects that could be further refined to improve the paper’s quality: first, the definition of core terms could be more precise, and supplementing chart information would enhance the paper’s readability and accuracy; second, expanding the model validation methods and deepening the discussion would help better confirm the reliability and innovation of the research conclusions; third, standardizing the reference format and updating the literature would improve the paper’s standardization and timeliness. It is suggested that the authors consider addressing these aspects in subsequent revisions.

The definition and usage of certain terms in the paper could be further clarified to facilitate readers' comprehension. For example, "freight tare coefficient", a core optimization criterion mentioned in both the abstract and Section 2.2.3, does not have a clear and unified definition when first introduced, with its meaning only indirectly reflected through Equation (7). Additionally, it is occasionally confused with "loading tare coefficient" in some subsequent chapters, which may lead to conceptual ambiguity for readers. Another example is "economic technical parameters (ETP)": defined in Section 1.21 as "technical parameters that significantly impact economic indicators such as cost and price", the term is later referenced in Section 3.2.2 as part of the "ETP program", but the connection between this program and the original ETP concept is not fully explained, resulting in insufficient coherence in term usage.
Figure 1, "Absolute Technical Parameters of Freight Wagons", labels certain parameters (e.g., 2Lw, 2L) but lacks legend explanations to clarify the positions and meanings of these key parameters. This makes it difficult for readers to correlate the symbols in the figure with the parameter descriptions in the text. Table 4, which serves as the core table for comparing parameters before and after optimization, also has room for improvement. While the paper mentions that "the volume of the optimized wagon is 37.957m³", the table has formatting inconsistencies and fails to fully present key comparative data, such as the tare weight and load capacity of both the original and optimized wagons. Consequently, readers cannot intuitively verify the actual effect of the optimization.The information presented in the paper’s charts and their explanatory content could be improved.
The paper only uses the Eamnos series open wagon as a single case for validation, without verifying the model's universality through different wagon types or freight data from diverse regions (e.g., non-EU countries). Meanwhile, the convergence test criteria for the iterative method in Section 3.3.2 are not clearly defined when calculating the optimization results. The paper only states that "the iterative process converges rapidly, and the exact solution can be obtained in the second or third iteration" but lacks supporting data such as specific iteration counts and error variation trends.
When deriving Equation (22), the physical meaning and value-taking basis of coefficients A, A', and C are not elaborated on, with only a brief mention later that "they are constants for specific wagon types". This may affect the model's understandability and reproducibility. Additionally, the model does not consider the dynamic factors of freight wagons in actual operation (e.g., the impact of vibration during driving on the load, changes in volume utilization under different road conditions), which limits the model's practicality to a certain extent and creates a gap with actual application scenarios.
The paper indicates that "after optimization, 3 operating wagons are reduced daily and 55 trains annually", it does not analyze the indirect impacts of this result on the transport capacity and scheduling efficiency of the railway network. It also does not discuss potential risks of the optimization scheme, such as restrictions on oversized cargo transportation caused by reduced wagon height and the safety impacts of adjusting the wagon body structure. Furthermore, comparing the study’s results with those of existing similar research would help clearly reflect the advantages and disadvantages of the proposed optimization scheme.
The references could be improved in terms of formatting consistency and timeliness. For instance, Reference [2] lacks the journal name and publisher location, while the ISBN number in Reference [5] is incomplete. Additionally, the citation formats for Chinese and English references are inconsistent, which affects the paper’s standardization. Moreover, the references include few recent research results published after 2020, with a lack of citations to new methods and technologies in the field of freight wagon parameter optimization in recent years. Supplementing the latest literature would help reflect the latest progress in the research area and enhance the timeliness of the references.

Author Response

Dear reviewer 3,

Best regards

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

In this paper, the authors propose a new criterion for optimizing the volume/specific area of universal freight wagons. They argue that the criterion currently used – the minimum low cost – is not practical in the realities of the modern world and provide a pertinent list of reasons to support this statement in Introduction. Authors analyse the technical optimization parameters, starting from the absolute technical parameters and introduce the relative technical parameters. Next, they present the optimization criterion, namely the cargo tare coefficient parameter and demonstrate that this criterion is proper. Finaly, the specific volume (area) optimization methodology and the methodology for determining the parameters volume, tare weight and load capacity of the optimized wagon are presented. Section Results and Discussion provides an illustrative example on how this new criterion operates considering a real open wagon series Eamnos.

Subject is interesting for railway industries and falls within the journal topic. Manuscript is relatively well documented.

Specific issues:

Introduction: fist paragraphs. Railway cars are not consumer goods, and therefore the number of producers and users is small at the national level. Accordingly, the procedure described at the beginning of the Introduction is practically not applicable. Producers launch a vehicle into production based on a firm order from a beneficiary and a specifications sheet that outlines the main characteristics of the vehicle, as well as the approval tests.
There are too many notations, and this aspect requires a table of notations.
Table 1 requires a reference or a methodology to calculate fimax.
Table 3 corresponds to one year, but a service life of a wagon spans 30-40 years. Regarding to the conclusion to decrease the tare weight by lowering the wagon height, what happens when the structure of the transported cargo is changed, and the optimised tare weight of the wagon requires to be either higher or lower?
6. More points should be represented for 0.6 < Vy < 1.1.
Authors propose to reduce the wagon height to have a lower tare weight, but it is not clear how much.

Author Response

Dear reviewer 4,

Best regards

Author Response File: Author Response.pdf

Round 2

Reviewer 4 Report

Comments and Suggestions for Authors

Manuscript has been partially improved. Here, the unsolved issues are presented.

Comment 1

Response 1: There is complete agreement between the authors and your thesis. The special thing here is that the proposed methodology is primarily aimed at the beneficiaries, so that they can offer the most effective construction possible for them, considering their own policy for carrying out transport activities.

Reviewer: Although the authors agree with the reviewer's comment, they do not improve the text.

Comment 2

Response 2: Agree. But such a table would be very long and would take up too much space in the article. Also, it is not obligatory to have such table according to formatting guidelines.

Reviewer: The same scenario: the authors agree with the reviewer's comment but find an excuse not to improve the text. Scattering the notations throughout the main text of the article does not help the reader. When there are many notations, practice shows that organizing them in the form of a table is necessary.

Comment 4

Response 4: Agree. Table 3 reflects the data for 2022 according to statistical data. Especially for the Republic of Bulgaria they are stable for the analyzed 15-year period, with a small growth observed. The correct approach proposed in the article is that the beneficiary should make a long-term (10-15 years) analysis of the transported cargo and forecast the trends for their change.

Reviewer: The authors indicate the solution in the response, but they do not add a corresponding brief comment in the manuscript.

Comment 5

Response 5: The number of points in Figure 6 and in this study cannot be chosen arbitrarily. It depends on the types of cargo to be transported, grouped by the “density” indicator. It is known that not all cargo can be transported in the standardized wagon categories.

Reviewer: A short comment should be added to address the reviewer’s observation.

Author Response

Dear reviewer 4,

Best regards

Author Response File: Author Response.pdf