Simulation and Experimental Analyses of Microscopic Traffic Characteristics under a Contraflow Strategy
Round 1
Reviewer 1 Report
This paper presents the microscopic traffic characteristics analysis for contraflow strategy and discusses the impact of moving bottlenecks under contraflow conditions. The overall quality of the paper is publishable. The topic is interesting and scientific. Here are some detailed comments
The title of this paper points out 'during mass evacuation'. However, in the paper, authors also points out under the experimental condition, driver mental conditions cannot be fully simulated. Therefore, is that possible rephrasing the title to make it more accurate, and updating the key words correspondingly.
Authors pointed out the fixed bottlenecks, such as contraflow entrance and exit, could affects the overall capacity and average speed. However, these fixed bottlenecks are not discussed separately. Instead, the overall average speed and speed variation are used to describe the traffic characteristics. Please explain the reason.
Is that possible to show the speed distributions of different operational conditions under different traffic volume rather than giving the average numerical analysis in Table 1?
Please mark the experimental route in Fig.1 rather than describing as 'the left blue one in Figure'.
If the background of Figure 1 is from Google Map. It is required to add the copyright info.
Line 125 'consider the flowing three reasons' should be 'the following three reasons'?
Line 207, 'in Figure 4' should be 'in Figure 1'?
Line 407 'coaches and tucks' should be 'coaches and trucks'?
Author Response
Dear Editor and Reviewer:
Thank you for your e-mail on 27 May 2019 and for the reviewer’s comments concerning our paper entitled “Simulation and experimental analysis with contraflow strategy of microscopic traffic characteristics during mass evacuation” (ID: applsci-503064). Those comments are all valuable and helpful for revising and improving our paper. We have carefully revised the manuscript according to your suggestions and marked the revised portion by the “Track Changes” function.
Our responses to the reviewer’s comments and suggestions are as flowing:
Point 1
The title of this paper points out 'during mass evacuation'. However, in the paper, authors also point out under the experimental condition, driver mental conditions cannot be fully simulated. Therefore, is that possible rephrasing the title to make it more accurate, and updating the key words correspondingly.
Response 1
Thank you for your precious comment. It is a very good suggestion for us to express the theme of the paper more accurately. The title was rephrased to “Simulation and experimental analyses of microscopic traffic characteristics under contraflow strategy”. The key words of “mass evacuation” and “traffic operation” were deleted, and “reversed lane”, “traffic scheme”, and “traffic simulation” were added correspondingly.
Point 2
Authors pointed out the fixed bottlenecks, such as contraflow entrance and exit, could affects the overall capacity and average speed. However, these fixed bottlenecks are not discussed separately. Instead, the overall average speed and speed variation are used to describe the traffic characteristics. Please explain the reason.
Response 2
1. Fixed bottlenecks are not discussed separately
(1) Thank you for pointing this out, and we agree that our manuscript should include more details and discussions about fixed bottlenecks of contraflow.
(2) Previous studies have done a great deal of researches on the entry-point and exit-point design of contraflow lanes to reduce the impact of fixed bottlenecks, and have made great progress. As mentioned in the Introduction Section, this paper mainly focuses on the moving bottlenecks cause by trucks and coaches.
(3) We added the introduction and explanation of fixed bottlenecks of contraflow in the Section 1 (Introduction) to make it more logical and clearer.
(4) We added the discussion of fixed bottlenecks at entrance and exits of contraflow respectively, and proposed suggestions for improving the passing speed of vehicles at crossover sections in the Section 3 (Analysis of traffic characteristics).
(5) We completed the statement of fixed bottlenecks in the Section 5 (Conclusion).
2. The reason why used the overall average speed and speed variation to describe the traffic characteristics
(1) During the data collection period, we selected 25 observation points severally along contraflow and normal lanes and 1 observation point at entrance and exit of contraflow lanes. The amount of traffic data we collected was too large, so we decided to use the average speed and speed variation to describe the traffic characteristics. In addition, the difference between the average speed of all points and points expect for entrance and exit points were small, so we use the average speed of all points expect for entrance and exit points to represent the overall average speed. The same is true with the average speed variation.
(2) Thank you for pointing this out. We added the details of observation points in Section 2 (Data collection), and added the speed and speed variation of entrance and exit of different operational conditions under different traffic volume Table 1.
Point 3
Is that possible to show the speed distributions of different operational conditions under different traffic volume rather than giving the average numerical analysis in Table 1?
Response 3
As mentioned above in Response 2, we revised the Table 1 as suggested. Correspondingly, the statement in Section 3 (Analysis of traffic characteristics) was revised.
Point 4
Please mark the experimental route in Fig.1 rather than describing as 'the left blue one in Figure'.
Response 4
We redrew the Fig.1 and numbered each contraflow segment. In addition, we revised “the left blue one in Figure 1” to “the No.1 contraflow section in Figure 1”.
Point 5
If the background of Figure 1 is from Google Map. It is required to add the copyright info.
Response 5
Thank you for your pertinent suggestion. The source and year of Figure 1 was added in the imagine caption as “Source: Google Map, 2018”.
Point 6
Line 125 'consider the flowing three reasons' should be 'the following three reasons'?
Response 6
We apologized for this error, and revised as suggested.
Point 7
Line 207, 'in Figure 4' should be 'in Figure 1'?
Response 7
We apologized for this error, and replaced 'Figure 4' with 'Figure 2'.
Point 8
Line 407 'coaches and tucks' should be 'coaches and trucks'?
Response 8
We are very sorry for our incorrect writing, and corrected this word as suggested.
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 appreciate for Editor and 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.pdf
Reviewer 2 Report
Generally this paper is not very well written. I have had a lot of trouble figuring out the graphs, figures, and tables. It needs a lot of work. I have stumbled over the misuse words and sentence structure. It needs an English review.
Author Response
Dear Reviewer:
Thank you for the reviewer comments concerning our paper entitled “Simulation and experimental analysis with contraflow strategy of microscopic traffic characteristics during mass evacuation” (ID: applsci-503064). The comment is valuable and helpful for revising and improving our paper. We have carefully revised the manuscript according to reviewer’s suggestion and highlighted the revised portion by the “Track Changes” function.
Point
Generally this paper is not very well written. I have had a lot of trouble figuring out the graphs, figures, and tables. It needs a lot of work. I have stumbled over the misuse words and sentence structure. It needs an English review.
Response
We apologize for the poor English writing of the manuscript. We then asked help from a peer reviewer with professional English writing skills to review it. Based on which we revised all the grammar and structure problems throughout the whole manuscript. In addition, all the figures and tables are checked and improved. We hope this will address your concerns and improve the readability of this paper. Please let me know if anything else is needed for improvement.
Author Response File: Author Response.pdf
Reviewer 3 Report
1. the reviewer is curious if any crashes occurred during the study period. If so, were they considered in the analysis. If not, how they should be considered.
2. As the anthers pointed out that most research of the contraflow strategy focus on the contraflow route selection and time estimation on the macro level, and few of them explore the traffic characteristics of contraflow segments on the micro level. So how the analysis on micro level will help improve evacuation efficiency.
3. The China Ministry of Communications has already changed to Ministry of Transportation, why in Shanxi Province, it is stilled called Communications Department of Shaanxi Province
4. Figure 1, the red segments will form bottlenecks for contraflow segments.
5. as the author indicated that without taking into consideration of driver behavior under real evacuation conditions, the results need to be adjusted, as well as the conclusions.
6. how the road capacity is determined and how the saturated and unsaturated flow conditions were defined in the study.
7. More information is needed for VISSIM model setup, calibration, model parameters.
8. Actually there are no queue formed in the study, redefine the passenger care queue and truck queue.
9. Statistical analysis is needed to compare the difference between normal lane and contraflow lane as well as the impacts of trucks.
Author Response
Dear Editor and Reviewer:
Thank you for your e-mail on 27 May 2019 and for the reviewer’s comments concerning our paper entitled “Simulation and experimental analysis with contraflow strategy of microscopic traffic characteristics during mass evacuation” (ID: applsci-503064). Those comments are all valuable and helpful for revising and improving our paper. We have carefully revised the manuscript according to reviewer’s suggestion and highlighted the revised portion by the “Track Changes” function.
Our responses to the reviewer’s comments and suggestions are as flowing:
Point 1
The reviewer is curious if any crashes occurred during the study period. If so, were they considered in the analysis. If not, how they should be considered.
Response 1
Thank you for pointing this out.
(1) No traffic accidents happened during the observation. To avoid the misunderstanding, we added the statement of traffic accidents in Section 2 (Data collection).
(2) It is noteworthy that no road accident occurred during the present field experiments. In the use of the contraflow strategy, special measures are required to prevent secondary accidents and reduce the effect of a crash. It should first be noted that most accidents that occur during contraflow are relatively minor, such as fender benders, scrapes, and side mirror rips. These types of small accidents are usually easily handled and can be solved rapidly. Second, if a serious accident that cannot be handled within a short time occurs, a new fixed bottleneck would be generated. In addition to regular measures, the road shoulder could be considered for temporary use by other vehicles to pass through. In the normal lanes, traffic cones and temporary road signs could be used to quickly guide drivers through the right shoulder. On the contraflow side, the inbound traffic can be directed through the right shoulder, while the contraflow traffic uses a short distance of the inbound lane to go around the accident. The discussion and explanation were added in the Section 4 (Moving bottleneck effect on contraflow lanes).
Point 2
As the authors pointed out that most research of the contraflow strategy focus on the contraflow route selection and time estimation on the macro level, and few of them explore the traffic characteristics of contraflow segments on the micro level. So how the analysis on micro level will help improve evacuation efficiency.
Response 2
This study is aimed at exploring the effects of contraflow through field experiments and traffic simulations for designers and mangers to better understand the contraflow strategy during mass evacuation. The evacuation efficiency could be improved from those aspects based on micro level:
(1) Since the fixed bottleneck at the entrance and exit points of contraflow lanes significantly limited the capacity of contraflow lanes that drivers needed to slow down to 25~35 km/h to pass it, it is suggested to set a wider cross section when constructing the highway. Besides, forbidding large vehicles across the highway median to contraflow lanes would increase the flow speed at entrance and exit points of contraflow.
(2) The study of moving bottleneck showed that the impacts of coaches on contraflow flow are relatively small and the impacts of trucks are large. It is necessary to adopt traffic operations to minimize the influence of moving bottlenecks caused by trucks. Four alternative operations of contraflow strategy were proposed and evaluated through Vissim simulations, and the recommended traffic operations of different traffic rate and truck ratio were provided for managers to refer.
(3) In addition, the study also found that when driving along contraflow lanes, drivers couldn’t see traffic signs from the opposite direction. It is recommended to set more traffic signs and boards to offer drivers comprehensive information and guidance.
Point 3
The China Ministry of Communications has already changed to Ministry of Transportation, why in Shanxi Province, it is stilled called Communications Department of Shaanxi Province.
Response 3
We apologized for this error, and replaced “the Communications Department of Shaanxi Province” with “the Department of Transportation of Shaanxi Province”.
Point 4
Figure 1, the red segments will form bottlenecks for contraflow segments.
Response 4
Thank you for pointing this out. Since the capacity of road sections without contraflow (the red segments) is lower than sections with contraflow, they become the bottlenecks of the whole road. In addition, due to the diverting flow at entrances and the merging flow at exits under contraflow strategy, congestions would form near the crossover section. The introduction and discussion of this problem were added in Section 3 (Analysis of traffic characteristics), and the correspondingly suggestions to improve the evacuation efficiency at crossover sections were added.
Point 5
As the author indicated that without taking into consideration of driver behavior under real evacuation conditions, the results need to be adjusted, as well as the conclusions.
Response 5
(1) Thanks for your suggestions. We revised the title of our article to “Simulation and experimental analysis of microscopic traffic characteristics under contraflow strategy” by deleting “during mass evacuation” since the field traffic data and Vissim simulations are all regular conditions without considering the driver behavior under real evacuation conditions.
(2) Besides, the results in the Section 3 (Analysis of traffic characteristics) and 4 (Moving bottleneck effect on contraflow lanes) were revised to be more accurate, and the explanation were added in the Section 5 (Conclusion).
Point 6
How the road capacity is determined and how the saturated and unsaturated flow conditions were defined in the study.
Response 6
Capacity is defined as the maximum rate on a roadway section during a given time under prevailing conditions. In Figure 2, the maximum traffic flow volume of contraflow and normal lanes are 1296 and 927 veh/hour/lane, respectively. That is, the road capacity of normal and contraflow lanes are 1296 and 927 veh/hour/lane, respectively.
According to the Chinese Highway Standard “Technical Standard of Highway Engineering JTG B01-2014”, when the V/C of a Highway is between 0.75 to 0.90, the level of service would be the fourth class. The four class means the operation of vehicle is significantly restricted by other vehicles. So when the V/C is larger than 0.75, we consider the traffic flow as saturated flow; when the V/C is smaller than 0.75, we consider the traffic flow as unsaturated flow;
Point 7
More information is needed for VISSIM model setup, calibration, model parameters.
Response 7
Thank you for your suggestions. One section was added in the Section 4.2 (Moving bottleneck effect of trucks) as the Section 4.2.1 (Vissim model development and calibration) to introduce the detailed information of Vissim model setup, parameters and calibration.
Point 8
Actually there are no queue formed in the study, redefine the passenger care queue and truck queue.
Response 8
Thank you for your suggestion. To be more accurate, we replaced “queue” with “platoon” in this article.
Point 9
Statistical analysis is needed to compare the difference between normal lane and contraflow lane as well as the impacts of trucks.
Response 9
(1) Thank you for your suggestion. The significant analysis between normal lane and contraflow lane under contraflow strategy was added in the Section 3.2 (Flow speed).
(2) In addition, the significant analysis of passenger car platoons speed between NR and NT scenario under contraflow strategy was added in the Section 4.2.2 (Vissim simulation results and discussions) to evaluate the impact of trucks.
Author Response File: Author Response.pdf
