Autonomous Vehicles for Enhancing Expressway Capacity: A Dynamic Perspective

Round 1

Reviewer 1 Report

The authors present a method and scenario for autonomous vehicles in expressway. However, the literature review is relatively poor. The authors should carry out better literature review to support and to identify new findings.

For example, the expressway capacity related to other aspects such as maintenance but the criteria for optimisation for this aspect is missing. Some work on expressway maintenance can be found here:

• Viaduct maintenance for future traffic demands and earthquakes | Infrastructure Asset Management (icevirtuallibrary.com)

The safety aspect and accidental related scenario should be included in the study such as in:

• https://saemobilus.sae.org/content/09-09-02-0007/

The authors should expand the criterial for optimisation and assure that the capacity enhancement considers all risk profiles. The weather and climate, logistic issues are missing such as in:

• https://www.mdpi.com/2225-1154/9/8/127
• https://www.frontiersin.org/articles/10.3389/fbuil.2021.685884/full

The authors should expand the criteria for optimisation. In addition, limitation of the work should be fully stated since the criteria have some limitation for application.

 

Author Response

Reviewer1：

The authors present a method and scenario for autonomous vehicles in expressway. However, the literature review is relatively poor. The authors should carry out better literature review to support and to identify new findings.

For example, the expressway capacity related to other aspects such as maintenance but the criteria for optimisation for this aspect is missing. Some work on expressway maintenance can be found here:

• Viaduct maintenance for future traffic demands and earthquakes | Infrastructure Asset Management (icevirtuallibrary.com)

Thanks for the reviewer’s suggestion. The recommend research is helpful, and relevant references have been added.

The safety aspect and accidental related scenario should be included in the study such as in:

• https://saemobilus.sae.org/content/09-09-02-0007/

The authors should expand the criterial for optimisation and assure that the capacity enhancement considers all risk profiles. The weather and climate, logistic issues are missing such as in:

• https://www.mdpi.com/2225-1154/9/8/127
• https://www.frontiersin.org/articles/10.3389/fbuil.2021.685884/full

The authors should expand the criteria for optimisation.

Thanks for the reviewer’s suggestion. Relevant references have been added.

In addition, limitation of the work should be fully stated since the criteria have some limitation for application.

Thanks for the reviewer’s suggestion. limitation of this work is stated in the last paragraph.

5.2 Future works

This research proposed a RC estimation and ROW method for expressway under MTF of HDVs, AVs and CAVs. However, the criteria have some limitation for application. First, the capacity formulation only considers fixed headway, while randomness of headway and its impacts on RC and ROW can be studied in the future works. Second, steady flow is ideal because vehicle lane changes, overpasses, and stop-and-go elements exist in real traffic flow, future works will consider these issues.

Author Response File: Author Response.pdf

Reviewer 2 Report

This is an interesting study. A model is developed to evaluate the impacts of AVs on reserved capacity of road infrastructure in a heterogeneous mixed traffic flow. This manuscript, however, needs to be improved. First, the language is vague and unclear, making it hard to digest the content. Second, model assumptions are not explained, making the readers wonder the validity of the results. A lot of simplification is made without justification.

Some specific comments are provided below. However, this is not an exhaustive list of the problems. The authors are encouraged to check and fix similar problems throughout the manuscript.

Lines 12-15: I am afraid that I don’t agree with this statement. Can the authors provide evidence supporting this statement? Specifically, I don’t know of any Avs and CAVs on the road (except for experiments). By the way, my impression of the phrasing “owing to” is that this phrase is typically used with something negative (i.e., negative causes).

Line 15: What are the “essential changes”?

Line 19: Is “verified” the same as “validated”?

Lines 21-22: This statement is rather vague. In fact, we don’t need to develop a model to figure this point. The problem here is the wording - “affect” is rather vague. Do you mean positively “affect” or negatively “affect”? and by how much? It needs to be quantified.

Line 23: What is “rapid” increase? What is “short-term”? Please provide quantifications.

Line 24: What is “long-term”?

Line 26: How much is the improvement? Please quantify.

Line 32: Please add reference(s).

Lines 33-35: run-on sentence – please divide it into two sentences for clarity. Check throughout the paper for similar issues.

Line 38: The wording “should be” is inappropriate here.

The rest of the first paragraph of the Introduction section: The authors need to give some context of China. Readers outside of China have no idea why the authors chose to focus on China. Besides, not all readers are familiar with “municipal authorities in China.” Why is this the motivation of this study?

Line 41: The wording “large-scale” is a bit confusing. Do the authors imply something is large scale based on investment or the spatial scale? If it is the latter, it is directly contradictory to line 43 – “8%” is a small number.

Lines 51-54: This statement is not true. “cars no longer require human-controlled driving tools” – then why are we still driving nowadays? Please also see the comment for “Lines 12-15.”

Lines 82-84: Please add reference(s).

Lines 96-98: Please add reference(s). Specifically, what is the evidence to support the word “most”? Why did the existing studies “did not sufficiently consider the complexity of heterogeneous traffic flow”?

Lines 99-100: While this statement might be true, the authors need to tell the readers why it is important. Just because something was not done before does not make it important. What are the hypotheses?

Lines 105-106: The phrase “in contrast to previous research” seems to contradict with the phrase in lines 99-100 “there is no study…”

Lines 119-120: What does “to highlight the essence of the problem” mean?

Line 125: What does “micro behaviors” refer to?

Line 126: What does “L1-L5” refer to? Is it the different levels of automation? I doubt general readers can figure it out.

Line 128: What does “wherein CAVs degrade to Avs” mean? Why is this assumption valid?

Line 130: What is the basis of “macroscopic”? Is it on spatial or temporal basis?

Lines 131-132: Why is this assumption valid? Apparently, it is very different from actual traffic.

 

 

 

 

 

 

Author Response

Reviewer2：

This is an interesting study. A model is developed to evaluate the impacts of AVs on reserved capacity of road infrastructure in a heterogeneous mixed traffic flow. This manuscript, however, needs to be improved. First, the language is vague and unclear, making it hard to digest the content. Second, model assumptions are not explained, making the readers wonder the validity of the results. A lot of simplification is made without justification.

Some specific comments are provided below. However, this is not an exhaustive list of the problems. The authors are encouraged to check and fix similar problems throughout the manuscript.

Lines 12-15: I am afraid that I don’t agree with this statement. Can the authors provide evidence supporting this statement? Specifically, I don’t know of any Avs and CAVs on the road (except for experiments). By the way, my impression of the phrasing “owing to” is that this phrase is typically used with something negative (i.e., negative causes).

Thanks for the reviewer’s suggestion. To make it more rigorous, the author change this description to “traffic flow on road networks will change from a homogeneous human-driven vehicle (HDV) traffic flow to a heterogeneous mixed traffic flow (MTF)…”

Furthermore ,The author change the phrasing “owing to…” to “With the rapid development of communication and autonomous-driving technology”.

Line 15: What are the “essential changes”?

Thanks for the reviewer’s suggestion, To make it more specific, the author change this description to “To understand the changes of MTF of transportation engineering…”

Line 19: Is “verified” the same as “validated”?

Thanks for the reviewer’s suggestion. According to our research, using the word “validated” is more appropriate

Lines 21-22: This statement is rather vague. In fact, we don’t need to develop a model to figure this point. The problem here is the wording - “affect” is rather vague. Do you mean positively “affect” or negatively “affect”? and by how much? It needs to be quantified.

Thanks for the reviewer’s suggestion, To make it more specific, the author change this description to “Both the MPR of AVs and CAVs can enhance the MTF RC, with a range of 0%-200%, and the platooning rate of CAVs have positive affect on the MTF RC”

Line 23: What is “rapid” increase? What is “short-term”? Please provide quantifications.

Thanks for the reviewer’s suggestion, To make it more specific, the author change this description to “CAV popularization does not necessarily lead to a rapid increase on transportation system efficiency when MPR is lower than 40%; however, it significantly improves the efficiency of existing urban transportation facilities when MPR is higher than 40%, the highest enhancement is 4800 pcu/h per lane in terms of RC”

Line 24: What is “long-term”?

Thanks for the reviewer’s suggestion, the change is shown in the last part

Line 26: How much is the improvement? Please quantify.

Thanks for the reviewer’s suggestion. To make it more specific, the author change this description to “a suitable ROW reallocation policy, that is, equipping CAV-dedicated lanes according to the MPR of AVs and CAVs, can enhance the capacity of expressway systems by 500 pcu/h per lane in terms of RC”

Line 32: Please add reference(s).

Thanks for the reviewer’s suggestion. Relevant references have been added

Lines 33-35: run-on sentence – please divide it into two sentences for clarity. Check throughout the paper for similar issues.

Thanks for the reviewer’s suggestion. Modifications have been made, similar issues have been checked

Line 38: The wording “should be” is inappropriate here.

Thanks for the reviewer’s suggestion. Modifications have been made.

The rest of the first paragraph of the Introduction section: The authors need to give some context of China. Readers outside of China have no idea why the authors chose to focus on China. Besides, not all readers are familiar with “municipal authorities in China.” Why is this the motivation of this study?

Thanks for the reviewer’s suggestion. Although the research problem exists in China, it is also a common problem in the world. The author will draw out the questions of this study from a broader perspective.

Line 41: The wording “large-scale” is a bit confusing. Do the authors imply something is large scale based on investment or the spatial scale? If it is the latter, it is directly contradictory to line 43 – “8%” is a small number.

Thanks for the reviewer’s suggestion. The ambiguous sentences have been cut out.

Lines 51-54: This statement is not true. “cars no longer require human-controlled driving tools” – then why are we still driving nowadays? Please also see the comment for “Lines 12-15.”

Thanks for the reviewer’s suggestion. The sentence in question has been changed to “cars will operate as a transportation robots with functions such as autonomous perception, decision-making, and execution”

Lines 82-84: Please add reference(s).

Thanks for the reviewer’s suggestion. Relevant references have been added.

Lines 96-98: Please add reference(s). Specifically, what is the evidence to support the word “most”? Why did the existing studies “did not sufficiently consider the complexity of heterogeneous traffic flow”?

Thanks for the reviewer’s suggestion. Relevant references have been added to support our judgment. Specifically, in order to show the existing studies “did not sufficiently consider the complexity of heterogeneous traffic flow” the author supplement that “In fact, AVs and CAVs exhibit different characteristics that should be considered separately, because CAV will generate much lower headway than AV when forming platoon. Furthermore, the form of CAV platoon in MTF is a random factor, where special considerations are required, and ROW management will also affect this randomness.”

Lines 99-100: While this statement might be true, the authors need to tell the readers why it is important. Just because something was not done before does not make it important. What are the hypotheses?

Thanks for the reviewer’s suggestion. This part is very important for this article, the author rewrite this part as “To the best of our knowledge, there is no study that has analyzed MTF capacity and ROW management simultaneously considering HDVs, AVs and CAVs, which will simultaneously appear on the road with variable penetration rate in the near future, the existing study on MTF capacity or ROW management under simplified MTF will not apply, especially for this dynamic situation. Therefore, this study proposes a theoretically RC quantitative model of MTF to address the combinational effect between the MPR of MTF and CAV platoon rates.”

Lines 105-106: The phrase “in contrast to previous research” seems to contradict with the phrase in lines 99-100 “there is no study…”

Thanks for the reviewer’s suggestion. The author changes the description to “In contrast to previous research which only consider simplified MTF,”

Lines 119-120: What does “to highlight the essence of the problem” mean?

Thanks for the reviewer’s suggestion. To make it more specific, the author change this description to“To highlight the essence of the problem without losing generality, Without losing generality”

Line 125: What does “micro behaviors” refer to?

Thanks for the reviewer’s suggestion. To make it more specific, the author change this description to “the micro behaviors of vehicles including car-following, lane-changing and CAV platooning”

 

Line 126: What does “L1-L5” refer to? Is it the different levels of automation? I doubt general readers can figure it out.

Thanks for the reviewer’s suggestion. “L1-L5” refer to the different levels of automation, and corresponding references are added.

Line 128: What does “wherein CAVs degrade to Avs” mean? Why is this assumption valid?

Thanks for the reviewer’s suggestion. To make it more specific, the author change this description to “Therefore, we simplified MTFs into three categories: HDVs, AVs, and CAVs. Specially, when a CAV follows an HDV or an AV, and there is no real-time interaction with the vehicle in front based on the internet-connected communication function, wherein CAVs degrade to AVs.”

Line 130: What is the basis of “macroscopic”? Is it on spatial or temporal basis?

Thanks for the reviewer’s suggestion. The authors rewrite this expression, see next.

Lines 131-132: Why is this assumption valid? Apparently, it is very different from actual traffic.

Thanks for the reviewer’s suggestion. The authors rewrite this expression to “For the sake of clearly presenting how to model traffic flow at the freeway segment, in this paper, we assume fixed headway as an estimate of the mean headway for a given car-following mode, which simplifies the model analysis and solution process.”

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The revision looks ok.

Somehow please improve English for final submission. There are quite a lot of grammatical errors.

Author Response

We thank the reviewer for your thoughtful suggestions and insights. The manuscript has benefited from these insightful suggestions. The manuscript has been rechecked and the necessary changes have been made in accordance with the reviewers’ suggestions.

The English of this manuscript is improved. We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper. We marked all the changes in the revised version of this manuscript.

We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the correction will meet with approval.

 

Once again, thank you very much for your comments and suggestions

Author Response File: Author Response.docx

Reviewer 2 Report

Thank you for addressing the comments. As I mentioned in the previous review, the specific comments provided are NOT exhaustive. The authors are still encouraged to continue to improve the readability of the manuscript by identifying similar issues.

Author Response

We thank the reviewer for your thoughtful suggestions and insights. The manuscript has benefited from these insightful suggestions. The manuscript has been rechecked and the necessary changes have been made in accordance with the reviewers’ suggestions.

In general, the author made the following modifications:

1. Improved the language of the article, making the sentence expression more clear.
2. The hypothesis of the study is modified, and the relevant references are cited.
3. The conclusions of this study are improved by using more accurate descriptions.

We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper. We marked all the changes in the revised version of this manuscript.

We appreciate for Editors/Reviewers’ warm work earnestly, and hope that the correction will meet with approval.