Acceleration and Deceleration Rates in Interrupted Flow Based on Empirical Digital Tachograph Data
Round 1
Reviewer 1 Report
This study tries to make a discussion about acceleration and deceleration rate determination in interrupted flow. Specifically, the author proposes an empirical formula to calculate acceleration and declaration length. However, it does not fit the scope of the journal and carries major issues such as:
- Literature review section is missing, consequently, the research gap is not identified by the author. There are only 6 studies (two of them belong to the author) cited in this paper which is not enough. The author needs to conduct an extensive literature review through recently published (over 5-10 years) studies to identify the gap.
- The aim of the study and its contribution is not clear.
- Section 2.2 proposes 77 study sites while section 2.3 proposes 120 study sites. Why?
- The author first start to talk about mainline and ramps which are mostly on motorways, however, they select only signalized intersections. It is conucing.
- Data Screening algorithm should be presented in detail, at least by providing Pseudo code in section 2.3 before Figure 4.
- Figure 4 is not readable as it is cropped. A new image is required.
- 3.1 (data collection): what is the general traffic composition in those study sites? how many private cars? what is the share of taxis, buses, and truck in the main and ramp traffic volumes?
- "passenger car behavior would be similar to those taxis". Is there any evidence or references for this statement?
- Table 5: what do you mean by "indiscrimination"?
- Section 4: is there any validation for formula 4?
- Conclusion: It is weekly presented and there is no discussion or conclusion on the contribution of the study, limitations, directions for further studies and so on.
Author Response
Thank you very much for your kind review. I attach the reply to your comments :)
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this paper, newly defined lengths of deceleration and acceleration lines are calculated and proposed, based on digital tachograph (DTG) data of vehicles stopped at signalized intersections at red lights. The language is clear and easy to read.
In the introduction part, the literature review is missing to justify the aim of this research. For example, some previous accident rate statistics would help the authors to justify the performance of this study.
Since only the digital tachograph (DTG) data of vehicles driven by professional drivers are respected (trucks, taxis, and buses ) in thy study and the usual everyday drivers are not respected, I'm wondering how can this influence the results.
What is more, gender has an important influence on driving behaviour, the same gender percentage from the population should be taken also in this study. Is it maybe clear to the authors that the gender representation of professional drivers in Sought Korea is the same as the population? If Yes, this should be stated in the paper, if not, this represents a serious gap in the study.
The part of the introduction with equations and tables should be transferred into methods.
In the conclusion part, the comparison between the ASSHTO and MOLIT should be also given in table 10. This will give the author quick and valuable information about the difference between the existing and the proposed new length.
Finally, the proposed length in this study and the currently defined length by MOLIT are obviously different. What is the reason behind changing the already defined minimum length? And how then can be changed the length of the already existing infrastructure?
Author Response
Thank you very much for your kind review. I attach the reply to your comments :)
Author Response File: Author Response.pdf
Reviewer 3 Report
Overall assessment
The paper deals with interesting issue on drivers’ dynamic behaviour at signalised intersections and generally is well structured. However, at current state the manuscript requires some corrections to improve its quality and clarity.
Some major comments
Introduction
Generally the literature review could be extended as there are a lot of other research devoted to drivers’ acceleration/deceleration behaviour considering different types of vehicles – that would enrich presented information in the introduction.
Data collection/sites description/Results
- basically test sites and data collection conditions are poorly described. There is no information on traffic and road characteristics (traffic intensity and composition, type of a cross-section of a road: single/dual carriageway) – it’s known that travel speed depends on those characteristics and so the deceleration values also depend on the initial speed so it’s worth to clarify that.
- it’s worth to specify if Authors collected data during peak/off-peak hours condition. If it was peak hours condition then it’s worth to provide information about traffic intensity.
- the research sites include urban and rural areas – Fig. 2 presents an example of intersection in the city area. It would be worth to present also an example intersection located in rural area. Additionally, signalized intersections are not commonly applied in rural areas so how to explain such a big number of those intersections in tested sites?
- There is no information about speed limits in urban and rural tested sites. At the same time it’s said that only vehicles with the speed over 200 km/h (!) were excluded from the data? Generally speed limit for urban areas is 50 km/h. For rural areas can be different so it’d be worth to specify that information.
- It’s stated that data with deceleration of higher than 20 m/s2 were excluded – on what basis did Authors set such extremely high threshold? It’s not usual for vehicles even for sudden unexpected breaking.
- For acceleration analyses Authors included in data vehicles with initial speed up to 35 km/h - why? It’s obvious that acceleration values will be significantly different for vehicles starting from stopped position and for those having initial speed 20 or 30 km/h. This should be clearly specified.
- Why did Authors set the acceleration threshold equal to 20 m/s2 – did they record any cases with so high values?
- The results are presented for trucks but it’s worth to specify the kind of trucks (single unit 2-axle, single unit 3 or more axles, single trailer 3 or more axles trucks) as their dynamic characteristics are different.
Auxiliary lanes
Maybe Authors should consider changing the title of this chapter to Discussion of results (or something else). Currently the article lacks the discussion of the achieved results of deceleration/acceleration lane lengths with the values given in applicable standards and presented in the Introduction (table 2) - this is the key issue of the paper. And how to refer the achieved results given in table 10 (specified for urban and rural areas) to the values given in table 2 without such a specification?
Some minor comments
- Line 96 - how to understand that the intersection is influenced by TRB?
- In table 3 it’s not clear what is Va parameter and why for each design speed there are assigned two values of Va,
- Fig. 5a - it should be specified for which area the data is presented in this Figure and it’d be worth to present data for the other area,
- Fig. 5a - it should be specified what vehicles are presented in this Figure ,
- Similar comments apply to Fig. 6.
Author Response
Thank you very much for your kind review. I attach the reply to your comments :)
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The authors should clearly state in the conclusion part that this research is valid only for professional drivers, that are much more expirienced compared to other drivers with unknown gender influence on the results. This can lead to serious gaps in the results which can cause even serious deficiencies on the site if applicated. Usually, the road geometry should be designed based on the weakest (least experienced) group of users and not the most experienced. Therefore the results of the study are correct but their usefulness is completely questionable.
Author Response
Dear Reviewer 2:
Thank you for your updated review comments. I follow your minor revision comment. In the conclusion chapter, I add some sentences as follows
- This empirical study result is valid only for professional drivers
- Road management authorities need to be careful when updating geometric design guidelines reflecting this study.
The detailed sentences are available in the revised version. Thank you.
