Battery-Assisted Trolleybuses: Effect of Battery Energy Utilization Ratio on Overall Traction Energy Consumption

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript analyzed whether there was a dependence between the percentage of battery and trolley line (TL) travel and the traction power consumption when operating BATs on bus or trolleybus lines. Overall, this is a very interesting and relevant study, and good to read. This manuscript also needs the following revisions.

1. The research significance of this study needs to be emphasized. The background and significance of this study needs to be elaborated in more detail in the introduction.

2. The description of the contribution of this manuscript is not obvious. The existing literature review simply described what each literature did, so it needs to be reorganized. The section of “5.2 Existing literature and research” in the last part of this manuscript needs to be written in the section of “1. Introduction” and the contribution of this manuscript needs to be spelled out.

3. This manuscript is lengthy and it is recommended that the content be appropriately simplified. For example,

1) The method chosen for the manuscript is the commonly used regression analysis method, but the manuscript does not improve on it. Therefore, it is recommended to simplify the description of the regression analysis method.

2) The drawing of the Boxplot in Fig. 1 is common sense and does not need to be explained in the manuscript.

3) The section of “4.3. Regression analysis results” also could be simplified.

Author Response

Dear Reviewer,

thank You for reviewing the article and providing relevant feedback. We highly appreciate the positive assessment of the study as a whole and, together with You, we notice the need to expand the study in the future, to support scientific research in the field of trolleybus transportation.

Comment 1: The research significance of this study needs to be emphasized.The background and significance of this study needs to be elaborated in more detail in the introduction.

Response1: Thank You for promoting this out. Within the introduction, we have added a short paragraph describing the significance of this study (lines 69-73), also in discussion (line 704 – 706). You were right, we didn't mention that within the introduction sufficiently.

Comment 2: The description of the contribution of this manuscript is not obvious. The existing literature review simply described what each literature did, so it needs to be reorganized. The section of “5.2 Existing literature and research” in the last part of this manuscript needs to be written in the section of “1. Introduction” and the contribution of this manuscript needs to be spelled out.

Response 2: Thank You for reminder. We have added a description of the benefits under the first point of this review. Discussion section 5.2 compares the results of the study with those found in practice or similar literature. We have changed the title of subsection 5.2 to clarify its intention.

Comment 3: This manuscript is lengthy and it is recommended that the content be appropriately simplified. For example,

1) The method chosen for the manuscript is the commonly used regression analysis method, but the manuscript does not improve on it. Therefore, it is recommended to simplify the description of the regression analysis method.

2) The drawing of the Boxplot in Fig. 1 is common sense and does not need to be explained in the manuscript.

3) The section of “4.3. Regression analysis results” also could be simplified.

Response 3:

1) We strongly agree, however, the scientific study is not only for the scientific community but also for practitioners such as public transport operators. We assume, however, that these professionals may not have sufficient experience with regression analysis issues. The article should therefore provide detailed guidance to enable employees of any public transport operator to develop a similar analysis in their own conditions independently.

2) Thank You, You are right. We remove boxplot's picture and difficult description from the manuscript.

3) Thank You for pointing this out. We have shortcut the introduction of all subsections in 4.3 and also texts around the tables and pictures, where was a lot of useless text.

Lines mentioned in the responses are valid, when revision in MS World is enabled.

 

Reviewer 2 Report

Comments and Suggestions for Authors

Overall, this essay is well written, well structured, logical and clear. This article focuses on the role of using battery-assisted trolley buses in energy conservation and emission reduction, trying to solve the problem of the development and popularization of environmentally friendly buses. 

Specifically, this paper draws out the relationship between its unit traction energy consumption and the ratio of battery-powered and trolleybus circuit vehicle operation by letting two battery-assisted trolleybuses run in Nicholina, battery-assisted trolleybuses running on conventional trolleybus routes, and so on. By using hybrids instead of engines, trolleybuses are preserved in urban public transportation operations. 

In addition, the main contributions of this paper are: the validation and characterization of the dependence of traction energy consumption on the proportion of BAT batteries and TL operation with a suitable model using mathematical-statistical and regression analyses; and the validation and simulation of the dependence of Rb/t on other selected variables that may be the cause or the consequence of the observed phenomena. 

In summary, the research methodology used in this paper risks the statistical dependence of the unit traction power consumption (Cut) of battery-assisted trolleybuses (BATs) on the ratio of battery and trolley line operation (Rb/t), the dependence of the auxiliary unit consumption, Acu, on the Rb/t and the dependence of the trolley line energy recovery, RTL, on the Rb/t. The conclusions found in this study make the transportation of trolleybuses and public transport vehicles more sustainable and thus deserve to be further promoted. 

Generally speaking, the article is well written, the structure is designed in a logical way, and the description is very detailed. However, there are also some errors about the grammar. If they were corrected, it would be more readable.

 

Line 16

Urban public transport companies around the world are introducing environmentally friendly bus solutions, ...

Urban public transport companies worldwide are introducing environmentally friendly bus solutions, ...

 

 

Line 25-28

The research also includes an analysis of battery-assisted trolleybuses operation on conventional trolleybus lines, which brought surprising findings, as well as an analysis of other selected indicators which can be dependent on battery run ratio. These findings can contribute to reducing traction energy consumption by simply modifying the operating technologies, without the need for extensive investment in infrastructure or vehicle equipment. 

The research also includes an analysis of battery-assisted trolleybuses’ operation on conventional trolleybus lines, which brought surprising findings, as well as an analysis of other selected indicators that can be dependent on battery run ratio. These findings can contribute to reducing traction energy consumption by simply modifying the operating technologies without the need for extensive investment in infrastructure or vehicle equipment. 

 

Line 35-36

Urban public transport plays a key role in meeting the sustainable development goals, particularly in reducing carbon emissions, increasing energy efficiency and minimizing urban congestion. 

Urban public transport plays a key role in meeting sustainable development goals, particularly in reducing carbon emissions, increasing energy efficiency, and minimizing urban congestion. 

 

 

 

Line 69

The paper consists of 7 chapters, beside the first chapter – Introduction, there is: 

The paper consists of 7 chapters, besides the first chapter – Introduction, there is: 

Line 72

... which includes data preparation, regression analysis and application of the selected model to a practical example, 

... which includes data preparation, regression analysis, and application of the selected model to a practical example, 

 

Line 74

... where the operational data of BATs in the conditions of the DPMŽ, the input data for the regression analysis, the actual results of the regression analysis and the application of the model in practice are described in detail, 

... where the operational data of BATs in the conditions of the DPMŽ, the input data for the regression analysis, the actual results of the regression analysis, and the application of the model in practice are described in detail, 

 

Line 728

Based on the results of the analysis, the key values of the Rb/t ratio in relation to the Cut were determined as: 

Based on the results of the analysis, the key values of the Rb/t ratio to the Cut were determined as: 

 

Line 739

... representing the average a BAT operating conditions within the DPMŽ, ...

... representing the average BAT operating conditions within the DPMŽ, ...

 

Line 747

The statistical dependence in this case was due to the seasonality of the bus line 67 operation and preference for the use of BATs on it. 

The statistical dependence, in this case, was due to the seasonality of the bus line 67 operation and preference for the use of BATs on it. 

 

Line 750

As Rb/t increased, the energy recovery to the TL decreases, ...

As Rb/t increases, the energy recovery to the TL decreases, ...

 

Line 757-758

The methodology presented in the study allows them to analyze their own operational data, verify the obtained results and adapt the models to the specific conditions of individual operators. 

The methodology presented in the study allows them to analyze own operational data, verify the obtained results, and adapt the models to the specific conditions of individual operators. 

 

Line 760

Thus, transport operating companies can optimize the operation of BATs, improve energy efficiency and contribute to the long-term sustainability of public transport in their cities. 

Thus, transport operating companies can optimize the operation of BATs, improve energy efficiency, and contribute to the long-term sustainability of public transport in their cities. 

 

Line 766-767

At the same time, a general methodology will be proposed to plan the hybrid operation of BATs in order to maximize the Rb/t value. 

At the same time, a general methodology will be proposed to plan the hybrid operation of BATs to maximize the Rb/t value. 

 

Line 774

... that makes them an even more sustainable alternative to conventional bus or trolleybus transport. 

... that makes them an even more sustainable alternative to conventional bus or trolley bus transport. 

 

Another problem is that the author only uses data from Slovakia, which questions the generalization ability of the method.  It is best for the author to verify his method in a simulation environment. If the author does not have time or due to the length of the article, he should at least tell the reader that there is a simulator called CARLA that can verify the method in the article, if the reader is interested. 

 

Xiang, Y., Wang, S., Su, T., Li, J., Mao, S. S., & Geimer, M. (2021, November). KIT bus: A shuttle model for CARLA simulator. In 2021 IEEE Industrial Electronics and Applications Conference (IEACon) (pp. 7-12). IEEE.

 

 

Dosovitskiy, A., Ros, G., Codevilla, F., Lopez, A., & Koltun, V. (2017, October). CARLA: An open urban driving simulator. In Conference on robot learning (pp. 1-16). PMLR.

  Comments on the Quality of English Language

see above

Author Response

Dear Reviewer,

thank You for reviewing the article and providing relevant feedback. We highly appreciate the positive assessment of the study as a whole and, together with You, we notice the need to expand the study in the future, to support scientific research in the field of trolleybus transportation. We are happy, that You have absolutely understood the study and You like the structure.

Comment 1: Generally speaking, the article is well written, the structure is designed in a logical way, and the description is very detailed. However, there are also some errors about the grammar. If they were corrected, it would be more readable.

Response 1: Thank you very much for pointing out the grammatical errors, and pointing them out in the text, including a proposal for correction. We have included all recommended grammar corrections.

Comment 2: Another problem is that the author only uses data from Slovakia, which questions the generalization ability of the method.  It is best for the author to verify his method in a simulation environment. If the author does not have time or due to the length of the article, he should at least tell the reader that there is a simulator called CARLA that can verify the method in the article, if the reader is interested.

Response 2: Thank you very much for your opinion. This study was designed as a pilot and its primary objective was to determine if there is a dependency of traction energy consumption on the ratio of battery vs. TL running, and how that dependency approximately behaves.

Based on the confirmation of this dependency, the plan is to extend the study in the form of a large-scale project based on the cooperation of several public transport operators (operated BATs) within the EU countries. This is lightly outlined in subsection 5.2 and also in the conclusion.

We also believe in the replicability of the methodology within the conditions of other operators when fitting the adjacent values from their conditions.

Thank you for introducing us to the CARLA software solution. We have never heard of it and are happy to learn about it. We will also report on the solution within the text (lines 732 - 736) and believe it is a suitable tool to detect the studied dependencies outside of real operations using simulations.

 

 

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript has been revised and is basically ready for publication. However, there is still a problem that has not been revised.

The existing literature review simply described what each literature did, so it needs to be reorganized. 

Author Response

Dear Reviewer,

thank You for your prompt revision of our article and also thank You for accepting the corrections from the last round of revisions.

Comments 1: This manuscript has been revised and is basically ready for publication. However, there is still a problem that has not been revised. The existing literature review simply described what each literature did, so it needs to be reorganized. 

Response 1: Dear reviewer, thank you for your comment. We have tried to write the literature review to the best of our ability and opportunity and the availability of appropriate literature. We recognize that the organization of individual studies is confusing; therefore, based on your recommendation, we have reorganized the section and reordered the studies presented according to their context.

Reviewer 2 Report

Comments and Suggestions for Authors

The problems have been addressed

Author Response

Dear Reviewer,

thank You for your prompt revision of our article and also thank You for accepting the corrections from the last round of revisions. We hope you will be satisfied with the article when it has been published.