Research on Speeds at Roundabouts for the Needs of Sustainable Traffic Management

The paper" Research on Speeds at Roundabouts for the Needs of Sustainable Traffic Management "is an active research on studying the drivers’ decision making regarding the speed selection behaviour. While the data collected for this study is interesting, it's not clear what the practical application of the study findings would be.

Despite the efforts of the authors in the following the present research, I find that the article lacks sufficient score to be published in the journal. However, considering some merit of the paper, I would like to go forward with paper and see how the authors try to resolve the required correction on the paper.

Following comments are some suggestions to authors

Dear reviewer, thank you for your comments and efforts to review our work. Traffic safety is one of the most important areas of traffic engineering and it is the subject of numerous studies aimed at increasing the level of safety and sustainability of traffic in urban areas. Traffic safety is inextricably linked to and dependent on other areas of traffic, especially the area of Traffic Management and Transport Planning. Through operational and design analysis, these areas are oriented towards identification of specific problems on the road and street network and the planning of solutions that enable the achievement of functionally optimal traffic conditions, ie the achievement of the highest possible Level of Service (LOS).In particular, the Highway Capacity Manual methodology is used to determine LOS at roundabouts and street artery segments in our region (http://www.trb.org/Main/Blurbs/175169.aspx), as well as the segments of street arteries in our region. Accordingly, the authors focused in this paper on researching and identifying models that can define speed at key segments of the roundabout, primarily for the needs of objective operational and design analysis for Traffic Management and Transport Planning. For the purpose of this paper, the authors made an extensive analysis of data collected at four intersections using a method that completely excludes changes in driver’s behavior. The focus was on determining the influence of geometric parameters of roundabouts on traffic flow velocities on roundabout segments (inflow gorge, roundabout zone and outflow gorge) and its impact on the level of service and emission of pollutants. The analysis showed a more or less significant mathematical dependence between a number of parameters of the geometry of roundabouts and speed. The importance of applying the paper results to sustainability, to time losses and estimation of pollutant emissions in different scenarios in cases of smaller and larger flow requirements is presented in the further course. Hence, the results of this paper can be applied in the field of Traffic Management and Transport Planning for more precise determination of traffic flow parameters, definition of service levels, determination of travel time and emission of pollutants at roundabouts and city arteries. We agree with your opinion that, in the context of speed dependence at the segments of the roundabout and geometric parameters, the results of this per can be applied in the field of traffic safety. However, the impact of the results on traffic safety has not been studied in this paper, since the emphasis is placed on other areas that are just as important as traffic safety for the sustainability of traffic in urban areas. In order to analyze the impact of circular geometry and speed by segments on traffic safety in a methodologically correct way, it would be necessary to analyze many other traffic safety indicators that were not the subject of analysis. Basically, a further course of research as a continuation of this work is the analysis of two of the four safety factors (vehicle and road). Such a research would be an excellent continuation of this paper, which would enable the analysis and planning of traffic conditions in the urban environment of Banja Luka, with the possibility of applying the results in other areas.

 Taking into account all the above and the importance of your comments as a reviewer, we have tried to comply as much as possible with the requirements in accordance with the real possibilities of this research.

1.     In first section, the motivation of the study in connection with the innovation of the idea or the necessity of doing the study should be defined according to the limitations of previous studies. The authors should refer to the importance and necessity of the subject of the research, which problems and limitations on the issue of traffic safety seem to encourage them to carry out the topic. Also, newer resources are needed.

The first section of the paper has been modified, with clarifications related to the motivation of the research, a novelty introduced by this paper with an emphasis on the possibility of application in the field of traffic safety.

2.     What is the status of your research topic on traffic safety? In other words, clearly state your innovation and new ideas in solving existing problems.

Section 1 emphasizes the importance of the results of speed research as a parameter of traffic flow on traffic safety, the importance and possibility of applying the results of the paper to traffic safety management. During operational and planning analyzes, especially when using application software, the proposed speed values at segments of roundabouts are mainly used, as a consequence of insufficient research. The paper shows the impact and significance of the use of objective values of speeds at roundabouts on the magnitude of time losses, and consequently on the level of service, as well as on the emission of pollutants.

If the planning analysis procedure determines that a roundabout would have negative impact on the level of service of a part of street network, other solutions must be considered, whereas those that provide the best level of service should be implemented, which significantly affects the creation of traffic safety management strategy and defining specific measures.

3.     A more sophisticated methodology would be required to draw more reliable conclusions.

Thank you for the comment. We have further improved the paper with regard to clarifying methodological approach in point 3.3.

4.     A discussion section should contain also comparisons with the findings obtained by others.

The paper is supplemented with quotations related to the impact of the road geometric characteristics on traffic safety, as well as the possibility of applying the research results in the field of traffic safety. The authors did not have the opportunity to perform a comparative analysis of the results obtained in other researches with the results presented in the paper. Namely, the researches in the mentioned papers are based on researches of the impact of geometric elements on the speed of individual vehicles. In this paper, we have focused on determining the impact of geometric elements on the traffic flow speed, which is a significant difference in the methodological approach. In the areas of Traffic Management and Traffic Planning, it is necessary to know the values of traffic flow speed in order to determine the level of service.

5.     Conclusion section is poor and brief. Authors should clearly describe the role of their research results in addressing traffic safety issues.

The Conclusion emphasizes the need to analyze the impact of the research results on traffic safety in the next stage of the research.