Vehicle Platooning: A Detailed Literature Review on Environmental Impacts and Future Research Directions

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

the paper is a detailed systematic literature review of the previous literature and this should be made more clear from the beginning / motivation of the paper or even from the title of the paper itself, consider changing it

as for the motivations, only 2) and 3) fit your contribution to the literature, point 1) is derived from other works

line 292-293 and following. Staring with the typo "Nomenclature". is the purpose of lines 293 - 314 the explanation of the variables included in table 2? i would make table 2 shorter without mentioning the math factors and add a discussion below where you discuss the main entries of the table in terms of maths and assumptions. some of the notation seems not correct to me

c_d is the drag coefficient, not Cd .. the same for c_h and c_f
rolling coefficient is r_r .. i cannot access the paper referred so i can't check why the author mention 3 contributors for the roll resistance (which is R_r instead than fr .. which is the Froude number in hydrology)
speed .. v[m/s], V[km/h] please clarify .. V = speed threshold is misleading, use V_max (or v_max)
there are two entries for T : integrated driving/braking torque and time threshold .. i would use alpha and beta instead than I and T, and define t_max the time threshold

check compliance with the rest of the paper if you accept my suggestions

why indentation from line 427?

445 - 458 , which is the description of the main limitation to this work, should be placed elsewhere (after line 554 maybe)

check the correspondence between references referred to in the paper and in the reference section: up to 40 we are ok; the first paper mentioned in table 2 is referred again as [40], but it should have been [41] .. in conclusion, the section "references" is ok, but you should check the paper accordingly

Comments on the Quality of English Language

fine

Author Response

the paper is a detailed systematic literature review of the previous literature and this should be made more clear from the beginning / motivation of the paper or even from the title of the paper itself, consider changing it 

We thank you for your careful review, and we agree with the reviewer's suggestion. The title has been changed to  “Vehicle Platooning: A detailed systematic literature review on Environmental Impact and Future Research Directions.“

as for the motivations, only 2) and 3) fit your contribution to the literature, point 1) is derived from other works

We understand the reviewer's point of view, and the abstract has been corrected accordingly. In particular, we removed the first point related to “identify simulation methods for platooning and for pollutant emission  and added" including the methods by which these are calculated" to the second motivation

line 292-293 and following. Staring with the typo "Nomenclature". is the purpose of lines 293 - 314 the explanation of the variables included in table 2? i would make table 2 shorter without mentioning the math factors and add a discussion below where you discuss the main entries of the table in terms of maths and assumptions. some of the notation seems not correct to me

c_d is the drag coefficient, not Cd .. the same for c_h and c_f
rolling coefficient is r_r .. i cannot access the paper referred so i can't check why the author mention 3 contributors for the roll resistance (which is R_r instead than fr .. which is the Froude number in hydrology)
speed .. v[m/s], V[km/h] please clarify .. V = speed threshold is misleading, use V_max (or v_max)
there are two entries for T : integrated driving/braking torque and time threshold .. i would use alpha and beta instead than I and T, and define t_max the time threshold

We removed the modelling tools from Table 2 and added that information below, where there is a discussion on the most commonly used methods to simulate or evaluate traffic, energy consumption, and pollutant emissions. By making this change, the nomenclature section was removed as it was no longer relevant. Changed Cd to C_d

check compliance with the rest of the paper if you accept my suggestions 

why indentation from line 427? 

 Thank you. We changed to the correct template formatting 

 

445 - 458 , which is the description of the main limitation to this work, should be placed elsewhere (after line 554 maybe) 

 

 Thank you for the suggestion. We moved this paragraph for the end of the discussion

 

check the correspondence between references referred to in the paper and in the reference section: up to 40 we are ok; the first paper mentioned in table 2 is referred again as [40], but it should have been [41] .. in conclusion, the section "references" is ok, but you should check the paper accordingly  

We changed the references in the text to the correct number. 

Reviewer 2 Report

Comments and Suggestions for Authors The manuscript has a very high number of editorial errors. 1. Figure 3 – resolution too low 2. Figure 4 – axis description illegible (Number of published documents per year and 1973 – 2021 and 0 – 310) - font too small 3. Figure 5 – axis description illegible; resolution too low 4. Table 2 - the layout of the table is unreadable; For the data entries that information was not available in the documents - do not use grey 5. Linie no. 293: „omenclature”? 6. Linie from 345 to 370 – lack of justification. 7. Figure 7 – This is not the Future Transport template (see: https://www.mdpi.com/journal/futuretransp/instructions) 8. Linie from 427 to 440 – justification.
Other comments are set out in the Annex

Comments for author File: Comments.pdf

Author Response

Reviewer 2

The manuscript has a very high number of editorial errors.

1. Figure 3 – resolution too low
2. Figure 4 – axis description illegible (Number of published documents per year and 1973 – 2021 and 0 – 310) - font too small
3. Figure 5 – axis description illegible; resolution too low
4. Table 2 - the layout of the table is unreadable;

 

R: The above-mentioned corrections were made.

Also, by suggestion of Reviewer 1 we changed the manuscript layout.

We apologize for not having noticed this issue in the last step of editing.

 

 For the data entries that information was not available in the documents - do not use grey

 

Grey literature generally refers to materials that are not published in traditional, peer-reviewed academic journals, and it was not used in tis review. We clarified this in the methodology chapter. While conference papers can offer valuable preliminary insights, our focus was on prioritizing research findings that have been subjected to a rigorous screening process. This decision aimed to ensure the review is built upon a bedrock of studies demonstrating established methodological soundness.

 

5. Linie no. 293: „nomenclature”? Removed

 

7. Figure 7 – This is not the Future Transport template (see: https://www.mdpi.com/journal/futuretransp/instructions)
8. Linie from 427 to 440 – justification.  Thank  you This was fixed

Changed CO2 to CO₂

Changed numbered list from (i) to 1., (ii) to 2. and (iii) to 3.

Fixed the remaining template formatting errors. We thank you for your careful review.

 

 

 

 

Reviewer 3 Report

Comments and Suggestions for Authors

·         Originality/Novelty and significance

The authors of the paper resume the subject of the road vehicle platooning.

The main merit of the work consists in identifying a collection of journal articles on the subject of "vehicle platooning" from the SCOPUS database.

The current work focuses on the potential effect that platooning can have on the reduction of emissions for heavy and light vehicles both on highways outside cities and in cities and identifies some references that address this topic.

However, the originality of the work cannot be properly assessed because it is not clearly addressed. Compared to the current state of the works, it is difficult to signal the news, both in the selection methodology of the analysed articles and not in the analyses made.

Previous works already address the car platooning subject with the necessary clarity, considering the objectives at the vehicle level, platoon level and at the third level, generally, beyond the platoon.

The choice of the subject of analysis is not fully justified, as long as the replacement of fossil energy with electric or hydrogen is closer than ever, and the number of electric cars is growing rapidly.

In addition, the efficiency of transporting large volumes of goods over long distances is much better in the case of electric railway transport, as this aspect is well known.

Therefore, choosing the subject of heavy-duty vehicle platooning should be justified very rigorously.

It is possible that for small volumes of goods (for the case of "last miles" distribution, for example), needs for the light-duty vehicle platooning may be identified, but rather in a mixed platoon.

The problem is more complex than it is approached in the paper.

As the novelty and necessity of freight vehicle platooning is not sufficiently demonstrated, the significance is difficult to assess.

  Quality of Presentation

The overall paper presentation is appropriate for a literature review.

However, in some parts the work has only narrative description, instead of a structure that is easier to follow (for example, in almost 100 lines from line 345 to 440, the explanations are only narrative). A better structuring of the descriptive parts is suggested.

 Scientific Soundness

1. The investigation starts from a work of the same nature, that is, a literature review (reference [33]), which discusses the objectives and factors that influence the creation of vehicle platoons. The reference establishes the objectives of the creation of platoons at three levels, namely, at the immediate level of the vehicle, then identifies the objectives of creation at the higher level, that of the platoon, and finally at a macro level, general objectives, beyond the platoon, and vehicle, objectives called "global level", divided into four objectives.

Taking these objectives from that paper as categories for the organization of the present review is not explained. The objectives of the formation of platoons are then transformed from "work categories" to "work areas" in Table 1. The inconsistency causes confusion for the reader.

In addition, the allocation of keywords to each of the four "categories" is not at all clear in Table 1. This table should be redone. It is the basis of the entire analysis. 

2. There is no explanation of the use in the first stage of selection, of only the word "platooning" (as a verb) and not the word "platoon" (as a noun), which is as important as the first.

3. Adequate justification for the choice of those keywords in Table 1 is missing.

4. No other keywords are used besides "emissions", appropriate words to help select works with the subject "environmental impact of platooning" (this is in paper title) as for example: "noises" or "carbon footprint", etc.

5. The explanation of the use of only the SCOPUS database is not sufficient. Platooning is possible only through ITS, and specific databases (e.g. IEEE) or other broad databases of the same nature are not used. The authors themselves admit that the search base could be the cause of a lack of relevance of some results.

6. The author does not explain clearly enough why conference papers are considered "grey" and are excluded, and what "grey" literature means.

In conclusion, the scientific soundness is not satisfactory, or at least not properly emphasized by the authors.

  Interest to the Readers

In the opinion of the reviewer, many readers may be interested in the topic of the paper, in finding papers dedicated to reducing emissions using truck platooning.

However, the work may disappoint some of the readers, due to the not very high merit of the soundness.

 Overall Merit:

Compared to other research on platoons, the analysis has average merit due to scientific shortcomings.

Author Response

Reviewer 3

 

     Originality/Novelty and significance

The authors of the paper resume the subject of the road vehicle platooning.

The main merit of the work consists in identifying a collection of journal articles on the subject of "vehicle platooning" from the SCOPUS database.

The current work focuses on the potential effect that platooning can have on the reduction of emissions for heavy and light vehicles both on highways outside cities and in cities and identifies some references that address this topic.

 

However, the originality of the work cannot be properly assessed because it is not clearly addressed. Compared to the current state of the works, it is difficult to signal the news, both in the selection methodology of the analysed articles and not in the analyses made.

Previous works already address the car platooning subject with the necessary clarity, considering the objectives at the vehicle level, platoon level and at the third level, generally, beyond the platoon.

The choice of the subject of analysis is not fully justified, as long as the replacement of fossil energy with electric or hydrogen is closer than ever, and the number of electric cars is growing rapidly.

 

The authors understand the reviewer's concerns. Regarding the novelty we tried to better emphasize this aspect in the introduction. Several review papers have been carried out on the topic of platooning. Prior articles have examined various aspects such as safety ​[26]​, transport planning ​[27]​, fuel economy ​[28]​, and microsimulation of longitudinal dynamics ​[29]​. However, to the best of the author's knowledge, none of the previous review papers have focused on the environmental aspects of platooning. In contrast, this review paper takes a unique approach by comprehensively exploring the environmental impacts of platooning, particularly in relation to air pollutant emissions and air quality. 

 

Regarding electrification, while advancements in electric and hydrogen-powered vehicles undeniably transform the transportation sector, the authors strongly believe that platooning technology offers potential benefits worth exploring even within this context. First the adoption of ele ctric and hydrogen technologies will take time. Optimizing current fossil-fueled vehicle usage during this period with platooning could reduce harmful emissions in the short and medium term (decades). Moreover, platooning strategies could potentially improve the efficiency of electric and hydrogen vehicles, extending their range and further facilitating their widespread adoption.  

We included this point in the discussion section what talking about air quality.  

 

 

In addition, the efficiency of transporting large volumes of goods over long distances is much better in the case of electric railway transport, as this aspect is well known.

Therefore, choosing the subject of heavy-duty vehicle platooning should be justified very rigorously.

The authors are aware that electric rail transport offers superior efficiency for large-scale freight movement over long distances." however, platooning of heavy-duty vehicles provides flexibility that rail transport cannot match. Road networks offer wider ability to adjust routes easily – an advantage in scenarios where door-to-door delivery is required or where rail infrastructure is less developed. Furthermore. platooning has a potential role to play in short to medium-haul transport, last-mile delivery scenarios, and in supplementing rail transport where flexibility is a priority. We also considered this point in the discussion.

It is possible that for small volumes of goods (for the case of "last miles" distribution, for example), needs for the light-duty vehicle platooning may be identified, but rather in a mixed platoon.

The problem is more complex than it is approached in the paper.

As the novelty and necessity of freight vehicle platooning is not sufficiently demonstrated, the significance is difficult to assess.

 

We understand the reviewer perspective. In fact, platooning has a potential role to play in short to medium-haul transport where faster deliveries are prioritized, in last-mile delivery scenarios where roads are less congested, and in supplementing rail transport for efficient movement of goods to and from freight hubs.

We introduced this topic in the discussion section “"Previous analysis has demonstrated the potential of platooning to reduce emissions and energy use, with an average 14% reduction in fuel or energy use for light-duty vehicles (LDVs) and a 13.2% reduction for heavy-duty vehicles (HDVs). While electric rail solutions continue to offer superior efficiency for large-volume, long-haul transport, platooning provides crucial flexibility and adaptability to complement traditional freight methods. To fully leverage platooning's benefits, several areas require further exploration. Below are 4 areas of future interest and development in the field of platooning and the environment:" 

 

 

  Quality of Presentation

The overall paper presentation is appropriate for a literature review.

However, in some parts the work has only narrative description, instead of a structure that is easier to follow (for example, in almost 100 lines from line 345 to 440, the explanations are only narrative). A better structuring of the descriptive parts is suggested.

 Scientific Soundness

1. The investigation starts from a work of the same nature, that is, a literature review (reference [33]), which discusses the objectives and factors that influence the creation of vehicle platoons. The reference establishes the objectives of the creation of platoons at three levels, namely, at the immediate level of the vehicle, then identifies the objectives of creation at the higher level, that of the platoon, and finally at a macro level, general objectives, beyond the platoon, and vehicle, objectives called "global level", divided into four objectives.

 

Taking these objectives from that paper as categories for the organization of the present review is not explained. The objectives of the formation of platoons are then transformed from "work categories" to "work areas" in Table 1. The inconsistency causes confusion for the reader.

 

In addition, the allocation of keywords to each of the four "categories" is not at all clear in Table 1. This table should be redone. It is the basis of the entire analysis.

We improved discussion and table accordingly. Building upon the comprehensive model presented in 'Taxonomy of Optimization Factors for Platooning' [33], this review focuses on four primary 'Areas of Work' directly relevant to environmental impacts: While [33] presents a wider taxonomy, this study focuses on areas impacting emissions, air quality, and resource usage.

 

2. There is no explanation of the use in the first stage of selection, of only the word "platooning" (as a verb) and not the word "platoon" (as a noun), which is as important as the first.
3. Adequate justification for the choice of those keywords in Table 1 is missing.

 

These keywords were derived from a preliminary analysis of terms commonly used within platooning studies. Additionally, keywords aimed to capture the broader thematic areas outlined in Sturm et al. [33].

4. No other keywords are used besides "emissions", appropriate words to help select works with the subject "environmental impact of platooning" (this is in paper title) as for example: "noises" or "carbon footprint", etc.

 

We acknowledge that our focus on the keyword 'emissions' likely limited the scope of our exploration regarding other significant environmental impacts, such as noise pollution. While our initial keyword set included broader terms like 'climate' and 'energy,' which indirectly relate to carbon footprint, a follow-up review confirmed that noise remains a significantly underexplored area within environmental platooning research.

 

 

5. The explanation of the use of only the SCOPUS database is not sufficient. Platooning is possible only through ITS, and specific databases (e.g. IEEE) or other broad databases of the same nature are not used. The authors themselves admit that the search base could be the cause of a lack of relevance of some results.

 

Thanks for your suggestion. SCOPUS database is often preferred due to its large collection of peer-reviewed literature, including scientific journals, books, and conference proceedings ​[32]​. A recent study found that SCOPUS was one of the most suitable databases for conducting systematic reviews. Moreover IEEE provides SCOPUS with all of the IEEE Xplore digital library content https://supportcenter.ieee.org/app/answers/detail/a_id/510/~/is-ieee-xplore-digital-library-content-indexed-in-scopus%3F

 

6. The author does not explain clearly enough why conference papers are considered "grey" and are excluded, and what "grey" literature means.

In conclusion, the scientific soundness is not satisfactory, or at least not properly emphasized by the authors.

Thank you for raising this point. Grey literature generally refers to materials that are not published in traditional, peer-reviewed academic journals. We clarified this in the methodology chapter. While conference papers can offer valuable preliminary insights, our focus was on prioritizing research findings that have been subjected to a rigorous screening process. This decision aimed to ensure the review is built upon a bedrock of studies demonstrating established methodological soundness

 

 

 

In the opinion of the reviewer, many readers may be interested in the topic of the paper, in finding papers dedicated to reducing emissions using truck platooning.

However, the work may disappoint some of the readers, due to the not very high merit of the soundness.

 

Compared to other research on platoons, the analysis has average merit due to scientific shortcomings.

Thank you for noting the relevance of emissions reduction through truck platooning, a topic with the potential to interest many readers. We take your assessment regarding the work's merit seriously and have carefully considered your feedback. 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Please just doublecheck the bibliography section and follow the standard format of the citations .. just an example

you wrote:

M. P. Lammert, A. Duran, J. Diez, K. Burton, and A. Nicholson, “Effect of Platooning on Fuel Consumption of Class 8 Vehicles Over 705 a Range of Speeds, Following Distances and Mass,” SAE Int J Commer Veh, vol. 7, no. 2, pp. 2014-01–2438, Sep. 2014, doi: 706 10.4271/2014-01-2438.

 

it should be

Lammert M.P., Duran A., Diez J., Burton K., Nicholson A.; 2014. Effect of Platooning on Fuel Consumption of Class 8 Vehicles Over a Range of Speeds, Following Distances and Mass. SAE Int J Commer Veh, vol. 7(2), pp. 2401-2438. doi: 706 10.4271/2014-01-2438.

Author Response

Thank you very much. We have remodelled the references as requested. 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors accepted the observations of the first report with some difficulty. Some introduced clarifications slightly improved the article, but the scientific merit remained moderate.

Author Response

Thank you very much for your careful review and comments.  We believe that after the revision the scientific robustness of our work has been improved.