Determination of Necessary Subsidiary Track According to Train Operation Frequency in a Heterogeneous Train Pattern
Round 1
Reviewer 1 Report
In this paper, a waiting time scheduling problem for different trains operated on the same track was investigated according to trans' operating frequencies. Then, the positions of the subsidiary tracks were analyzed and effects on the train operation service were evaluated. This problem can be formulated as a NP hard problem. Instead of using the existing using heuristic methods, a genetic algorithm was proposed. It is an interesting research. However, this paper should be improved in the following aspects before it is considered for acceptance.
- Since this problem can be formulated as a NP hard problem, the objective function should be listed;
- The genetic algorithm used to solve this problem should be clearly presented as pseudo code in the paper;
- Improve the equations' quality. How to calculate the sum in Eq. (9) should be indicated;
- How simulation was conducted shoud be descripted.
In summary, this paper should be improved before it is considered for acceptance.
Author Response
1. Since this problem can be formulated as a NP hard problem, the objective function should be listed
Answer: The objective function is included in line 267 to 272 and represented in Equation (10).
2. The genetic algorithm used to solve this problem should be clearly presented as pseudo code in the paper
Answer : I added 3.4 Structure of genetic algorithm. I added a flow chart of genetic algorithm and pseudo codes related to 3.4 have added with explanation from Table 6 to 12.
3. Improve the equations' quality. How to calculate the sum in Eq. (9) should be indicated
Answer : I revised Eq.(9) and explained about Eq.(9) in line 239 to 266. For Eq.(9), The minimum headway is a key parameter in selecting the subsidiary tracks that can be used when high-speed trains pass low-speed trains. This study requires the subsidiary tracks for overtaking of high-speed trains. To analyze the minimum headway between trains, a line with the longest distance between stations is selected in a station with subsidiary tracks from which a low-speed train has started. For the following high-speed train to run at a non-braking speed, the time when the preceding low-speed train arrives at the station with subsidiary tracks and the guaranteed minimum headway to be overtaken by following high-speed are required.
4. How simulation was conducted should be descripted.
Answer : How simulation was conducted was descripted at 4.1 and Line 393 to 405 was added.
Reviewer 2 Report
General comments: This work performed simulation using the genetic algorithm on heterogeneous train operation. The train operation frequency was used to calculate scheduled waiting time aiming at providing information on determining appropriate subsidiary track at intermediate stops.
Specific comments:
- Line 29 and 30: The point of the last two sentences of the first paragraph is not clear. Very confusing.
- Double check the grammar of the first sentence of the second paragraph in Line 31-32.
- Line 133-139: The author described the goal of this work but did not clearly say why choosing this goal. With applying optimization techniques, the author is able to do many things, but the question is this objective instead of others?
- Why was simulation performed 100 times? Not more or less?
- The author said in the end of Abstract that “This finding clearly shows that the operation pattern and speed of trains are related to overtaking.” Is this conclusion obvious? I believe most people can reach such conclusions without any simulation.
- What confused this reviewer most is why do this investigation. The impact of this work seems very little. What is the real point of this work? The methods? The results (not obvious to me)?
Author Response
1. Line 29 and 30: The point of the last two sentences of the first paragraph is not clear. Very confusing.
Answer : I revised the sentences in line 29-32
2. Double check the grammar of the first sentence of the second paragraph in Line 31-32.
Answer : I revised the sentences
3. Line 133-139: The author described the goal of this work but did not clearly say why choosing this goal. With applying optimization techniques, the author is able to do many things, but the question is this objective instead of others?
Answer : Sentences of line 134-143 are explanation of the goal of related studies. I have changed some sentences in order to avoid confusion.
4. Why was simulation performed 100 times? Not more or less?
Answer : When operating three types of trains simultaneously, various train schedules are analyzed according to the train departure order. So I continued to simulate and judged that 100 times was enough to get the result. Of course, I have simulated more than 100 times. However, I decided that it was enough to get the result by deciding the standard of the number of simulations for each case.
5. The author said in the end of Abstract that “This finding clearly shows that the operation pattern and speed of trains are related to overtaking.” Is this conclusion obvious? I believe most people can reach such conclusions without any simulation.
Answer : I agreed with your opinion. The reason i wrote that sentence is that i would like to represent that it was derived an objective and reliable results than railway planner’s experience rule. I have changed the sentence that the results of this study are expected to facilitate objective and practical railway planning in railway construction. And the abstract was little bit revised for understanding.
6. What confused this reviewer most is why do this investigation. The impact of this work seems very little. What is the real point of this work? The methods? The results (not obvious to me)?
Answer : The ultimate objective of this study is to increase the objectivity and reliability by determining the location of the main station of the railway station in an analytical method, rather than determining the location of the main station of the railway station as a planner’s experience rule. It will be possible to provide an objective basis for the railway planning, rather than simply relying on the subjective experience of planners. Furthermore, if the subsidiary tracks are analyzed based on the method proposed in this study when a new railway line is constructed in a developing country, then it will help achieve economic and policy feasibility.
Reviewer 3 Report
In this paper the Author makes use of meta-heuristics algorithm, specifically the genetic algorithm, to assess the need of subsidiary tracks in intermediate stations based on the operation frequencies of different trains. Specifically, passenger, freight and high-speed trains are considered in this study in a route made up of seven stations in total, with five intermediate stations. Six different cases are analyzed and several simulations are carried out to assess the need of the subsidiary track in one or more of the intermediate stations.
The manuscript is interesting, fits well with the aim of the “Applied Sciences” Journal, but can be reconsidered for publication after the described major revisions.
Specifically:
(1) At line 148, the Authors writes: “The value of the scheduled waiting time is tw, k + 1”. Please, explain the complete meaning of the subscript here.
(2) In Figure 2, the label of the X-axis is missing. Please, correct.
(3) Equations (3-5) and (6-8) might not be clear to the reader. Please, write them in a clearer way and explain all the elements contained within the Equations.
(4) In the same way, Eq. (9) and the content of Figure 4 should be explained in more detail.
(5) The six cases presented in section 4.1 are not clearly presented. Also, some of them seem to be absolutely identical in the text description (e.g. see cases 5 and 6). In the same way, Table 6 should be adjusted in order to let the reader to understand more clearly and easily the differences among the six considered cases.
(6) Figure 9 is not the correct one, as it is identical to Figure 12 which refers to case 3. Please, provide the correct image for case 2, which should show a peak of 27 times out of 100 simulations corresponding to the 11 min scheduled waiting time (lines 354-355).
(7) Finally, the work seems interesting but rather limited to the very simplified example reported by the Author. At least, few remarks should be provided on the application of the proposed methodology to more complex patterns of stations and trains (different types of passenger, high-speed and freight trains, more complex station network, etc.).
According to what said above, the reviewer’s opinion is that the manuscript can be reconsidered for publication after the described major revisions.
Author Response
1. At line 148, the Authors writes: “The value of the scheduled waiting time is tw, k + 1”. Please, explain the complete meaning of the subscript here.
Answer : I revised figure 1 and added explanation about tw. tw is waiting time of low speed train because of overtaking high-speed train. The preceding low speed train should wait at a station until passing high-speed train at a station. Scheduled waiting time is the time between arrival time at the station and departure time at the station after passing a high-speed train.
2. In Figure 2, the label of the X-axis is missing. Please, correct.
Answer : I added the label of the X-axis in figure 2. Nt is number of trains.
3. Equations (3-5) and (6-8) might not be clear to the reader. Please, write them in a clearer way and explain all the elements contained within the Equations.
Answer : When a high-speed train overtakes a preceding low-speed train (passenger or freight trains), the guaranteed arrival headway of the high-speed train without reduction of speed by a preceding low-speed train and the guaranteed departure headway of the low-speed train after passing the high-speed train are represented by equation (3)~(8). By subtracting the arrival and departure times of the preceding train from the arrival and departure times of the subsequent train, the headway for the arrival and departure times of the preceding train and the following train can be estimated at the station. I have added above sentences in line 226 to 232.
4. In the same way, Eq. (9) and the content of Figure 4 should be explained in more detail.
Answer : I revised Eq.(9) and explained about Eq.(9) in line 255 to 266. For Figure 4, The blocking time finishes after the train has completely left the section and all signaling appliances have been reset to normal position so that movement authority can be issued to another train to enter the same section. Therefore, the blocking time of a track section is usually much longer than the time the train occupies the section. I added explanation of the Figure 4 in line 239 to 253.
5. The six cases presented in section 4.1 are not clearly presented. Also, some of them seem to be absolutely identical in the text description (e.g. see cases 5 and 6). In the same way, Table 6 should be adjusted in order to let the reader to understand more clearly and easily the differences among the six considered cases.
Answer : I revised and added some sentences to understand more clearly in line 393 to 419 and Table 6 was revised.
6. Figure 9 is not the correct one, as it is identical to Figure 12 which refers to case 3. Please, provide the correct image for case 2, which should show a peak of 27 times out of 100 simulations corresponding to the 11 min scheduled waiting time (lines 354-355).
Answer : I revised Figure 9.
7. Finally, the work seems interesting but rather limited to the very simplified example reported by the Author. At least, few remarks should be provided on the application of the proposed methodology to more complex patterns of stations and trains (different types of passenger, high-speed and freight trains, more complex station network, etc.).
Answer : The ultimate objective of this study is to increase the objectivity and reliability by determining the location of the main station of the railway station in an analytical method, rather than determining the location of the main station of the railway station as a planner’s experience rule. To increase objectivity and reliability, it is necessary to study based on various railway environments. Although the distance between stations is the same in this study, the actual railway route is composed of various distances between stations. As a result, the speed and driving time of the trains considered vary. In addition, it is necessary to apply the number of times of operation of each train based on transportation demand to be applied in actual operation. If this study is complemented in the future, it is expected to increasingly facilitate objective and practical railway planning in railway construction. I added some sentences in Line 648 to 657
Round 2
Reviewer 1 Report
In this paper, a waiting time scheduling problem for different trains operated on the same track was investigated according to trans' operating frequencies. Then, the positions of the subsidiary tracks were analyzed and effects on the train operation service were evaluated. This problem can be formulated as a NP hard problem. Instead of using the existing using heuristic methods, a genetic algorithm was proposed.
In this revision, the paper has been improved by addressing reviewers' comments. However, the objective function and constrain conditions were still not clearly presented in the revision. Is this research to address the waiting time scheduling problem and/or determinate the positions of the subsidiary tracks? The objective function is for determinate the positions of the subsidiary tracks. How about the waiting time scheduling? How to optimize? What are the constrain conditions?
In summary, the paper has been improved. However, it should be further improved.
Author Response
Is this research to address the waiting time scheduling problem and/or determinate the positions of the subsidiary tracks? How about the waiting time scheduling?
--> In this research, the scheduled waiting time should be considered in order to determine the positions of the subsidiary tracks. The scheduled waiting time is calculated when a preceding low-speed train waits for overtaking a follow-up high-speed train at a certain position. The certain position is the position of the subsidiary tracks in this research. The objective of this research is to determine subsidiary tracks when operating heterogeneous trains on a same track. Therefore, the scheduled waiting time should be mentioned to achieve the objective of this research.
That above mentioned was added in the manuscript in line 149 to 153.
How to optimize?
--> In this research, the method of optimization uses the genetic algorithm. The genetic algorithm can solve optimization or decision-making problems because its concepts and theory are simple, and it has demonstrated excellent performance when searching for numerous random solutions set by researchers. In particular, the genetic algorithm is appropriate for solving problems with many variables and constraints because of its excellent search function in a complex solution space. Furthermore, the high flexibility of this model provides the advantage of facilitating the addition of constraints and the modification of the objective function. In the present research, a genetic algorithm was applied to determine the position of subsidiary track. The explanation for the method of optimization was mentioned in line 87 to 94.
What are the constrain conditions?
--> There are constrains when operating heterogeneous trains on a same track. The waiting time function, the guaranteed headway for high and low-speed trains at a station, the blocking time and the minimum headway were considered as the constrain conditions in this research. Polynomials for the constrain conditions were mentioned in line 169 to 266. And also, differences for each train such as operation frequency, dwell time, velocity, stopping station are regarded as the constrain conditions when doing simulation.
That above mentioned was added in the manuscript in line 629 to 633.
I appreciate your thoughtful suggestions and insights.
Reviewer 2 Report
This reviewer does not have any more questions.
Author Response
I appreciate your thoughtful suggestions and insights.
Reviewer 3 Report
After having carefully read the manuscript, it can be said that the suggestions of the Reviewer have been fulfilled by the Authors, and the original paper has been correctly amended and improved.
Therefore, the paper can be published in its current form.
Author Response
I appreciate your thoughtful suggestions and insights.
