Speed Behavior of Heterogeneous Traffic on Two-Lane Rural Roads in Malaysia
Round 1
Reviewer 1 Report
The manuscript focuses on exploring and understanding the speed behaviour while a vehicle moves on curves.
General comments:
English must be improved, as well as formatting issues (missing capital letters, spaces, italic format for 'p'-value on L278, etc) must be corrected (e.g., lines 84, 88, 90). While citing a table, this should be like 'Table 1', 'Table 2',...
A careful revision must be performed.
L93-94: motorcyclists -> motorcycles (it is regarding a vehicle class).
Please, be careful with the writing... clearly mention what is written in lines 96-98. This is not a report, it should be a scientific manuscript.
At the end of Section 2, it should be included the novelty of the present research, as well as as its contribution to the state-of-the-art.
Under Section 3, which is related to the methodology followed in this work, the site description should be the last subsection. This should start by giving details on how the authors collected data for conducting this study. Then, specific details should be given concerning how data will be treated and analysed. Only then, the case study in particular should be described.
Additionally, it must be explained why the Tukey post hoc test is the right choice. I suggest to include some sentences so that the reader may get the relevance of using this test.
Results Section must be divided into subsections to ease the reading.
No limitations, beside a simple small sample/case study, were found in the present study, which is a concern to me. I suggest to include some words on that and possibly, devote a subsection for it.
In Conclusions Section, no future research directions are mentioned.
Based on my revision, it is my opinion that the manuscript needs major revisions to be possibly considered ready for publication in high-quality journal.
Author Response
Please review the responses attached.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This study explores the speed behavior of different vehicle classes on two-lane rural roads in Malaysia. The data (speed, headway, timestamp, and vehicle classification) have been collected from automatic traffic counters. Overall, the paper is well-written and some interesting findings have been obtained. My main concerns are as follows;
- Abstract is too long. The authors may consider shortening it by keeping only necessary items.
- Related works and in particular, lines 66-68 - Operating speed OR the 85th percentile speed is not essentially the free-flow speed. That is, they are defined differently. In general, to determine free-flow speed, spacing or headways or sometimes traffic conditions are considered. Please make sure that the right terms/ definitions for speeds. Please have a look at the following papers.
Misaghi, P., & Hassan, Y. (2005). Modeling operating speed and speed differential on two-lane rural roads. Journal of Transportation Engineering, 131(6), 408-418.
Montella, A., Pariota, L., Galante, F., Imbriani, L. L., & Mauriello, F. (2014). Prediction of drivers’ speed behavior on rural motorways based on an instrumented vehicle study. Transportation Research Record, 2434(1), 52-62.
Dias, C., Oguchi, T., & Wimalasena, K. (2018). Drivers’ speeding behavior on expressway curves: exploring the effect of curve radius and desired speed. Transportation research record, 2672(17), 48-60.
Furthermore, there are may previous works on operating speed and free-flow speed analyses. Related Works section can be improved by adding such previous works.
- Section 3 - When vehicles are mixed, how the 85th percentile speed was determined? Was it determined for each vehicle category? It is quite unclear how it was estimated when vehicle flow is heterogeneous. Probably, a figure can be provided to explain the way of estimating 85th percentile speed.
- Fig. 4 - The authors have mentioned that "classes. The 85th percentile operating speed for all vehicle classes at different points is presented in Figure 4. " (on lines 220-221). Does this mean that the 85th percentile speed was estimated at different points and later the points (in Fig. 4) were connected? OR were the continuous speed profiles estimated? As I mentioned earlier, 85th percentile speed and free-flow speed are different definitions.
- It is interesting to note that the seeding patterns are changing for some vehicle classes (e.g., LV and MC on Fig. 5 left, LV and MC on Fig.7 for Radius 297). What could be the reasons for such differences?
- Captions of Fig. 6 and 7 are provided as "Time Behavior". What is meant by this?
- Finally, even though the title of this paper is related to “road safety” the content of the paper is about “operations” as 85th percentile speed is mainly used in highway designs, performance analysis, etc. rather than for evaluating safety. Further, I cannot see any discussions on road safety implications based on the findings of the paper. Probably, the authors may consider changing the title of the paper.
Author Response
Please review the responses attached.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The manuscript has been improved and most of my concerns were addressed in the revised version, and it can therefore, be considered for possible publication in the Journal.
Reviewer 2 Report
The authors have addressed the comments provided by the reviewer. Furthermore, the paper has also been modified accordingly.
I have no further comments.
