Correlation of Road Safety Criteria with Occupant Safety Criteria in Impacts on Crash Cushions
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe objective of this paper is to compare occupant criteria for different body regions (head, neck, chest and upper legs, shoulder) with road safety criteria (ASI, THIV/OIV, PHD/ORA) utilizing crash tests against crash cushions with passenger cars commonly used in EN 1317 and passenger cars with improved occupant safety equipment (airbag, seat belt pre-tensioner and load limiter).
In fact, The data in this paper comes from another article by the authors—“Impacts on Crash Cushions—Analysis of the Safety Performance of Passenger Cars with Improved Safety Equipment Compared with Test Vehicles Based on Assessment Criteria as Defined in EN 1317”. Of course, This is not in conflict because the study is a further development of the previous work.
Some suggestions can be considered. (1) Some test pictures can be added; (2) Some test data can be supplemented.
Author Response
The objective of this paper is to compare occupant criteria for different body regions (head, neck, chest and upper legs, shoulder) with road safety criteria (ASI, THIV/OIV, PHD/ORA) utilizing crash tests against crash cushions with passenger cars commonly used in EN 1317 and passenger cars with improved occupant safety equipment (airbag, seat belt pre-tensioner and load limiter).
In fact, The data in this paper comes from another article by the authors—“Impacts on Crash Cushions—Analysis of the Safety Performance of Passenger Cars with Improved Safety Equipment Compared with Test Vehicles Based on Assessment Criteria as Defined in EN 1317”. Of course, This is not in conflict because the study is a further development of the previous work.
Some suggestions can be considered. (1) Some test pictures can be added; (2) Some test data can be supplemented.
Comment 1: Some test pictures can be added
Response 1: Thank you for pointing this out. We have included quite much pictures in the previous paper and would not include them again. Instead, the first paper is referenced. We hope that suits too.
In line 280 we have changed the text to
“A detailed description on the results of the road safety criteria and damage pattern of the vehicles are given in Tomasch and Gstrein.”
Comment 2: Some test data can be supplemented
Response 2: Thank you for pointing this out. We agree with this comment. Therefore, we have included the test data in the appendix.
In line 282 we have added following text
“Corresponding curves of the time relationships for the criteria are in the appendix B.”
Reviewer 2 Report
Comments and Suggestions for AuthorsThe study investigates the correlation between road safety criteria and occupant safety criteria and its effect on crash cushions. Overall, the paper is easy to follow. The reviewer has a few minor comments.
1. The contributions of this study should be presented clearly.
2. The limitations of this study and future research directions should be provided as well.
Author Response
The study investigates the correlation between road safety criteria and occupant safety criteria and its effect on crash cushions. Overall, the paper is easy to follow. The reviewer has a few minor comments.
Comment 1: The contributions of this study should be presented clearly.
Response 1: Thank you for pointing this out. We agree with this comment. Therefore, we have added some text in the conclusions.
line 575
The study was able to show that the assessment of road restraint systems using the existing ASI and THIV criteria does not necessarily reflect the risk of injury to oc-cupants when compared with corresponding occupant criteria such as HIC. The study showed that there is a huge difference when the criteria are associated with injury risks. According to the study of Gabauer and Gabler [61] the worst THIV identified within the tests would result in an injury risk of approximately 66 % for an occupant sustaining MAIS 2+ injuries. Based on the HIC, however, the risk of sustaining MAIS2+ injuries to the head would be approximately 10 % according to Hertz ([62] cited in [40]). This is quite a large difference, as both criteria should actually be used to assess the risk of injury. However, the tests also showed that vehicles with improved safety equipment perform significantly better.
Comment 2: The limitations of this study and future research directions should be provided as well.
Response 2: Thank you for pointing this out. We agree with this comment. Therefore, we have included a new chapter – Limitations and Future developments.
In line 558 we have included a new paragraph (Limitations):
The analysis of the data comprises only four tests. The calculated correlation is therefore based on a small sample size. This may lead to results that cannot be fully explained, as in the case of THIV and OIV, for example. No positive correlation was observed between THIV or OIV and HIC or a3ms head acceleration, but this was ex-pected as these two criteria are used to assess the risk of head injury. This may also be due to the small sample size, although the ASI correlates positively with the HIC and a3ms head acceleration.
Only one test was carried out in each test configuration. Thus, the influence of different impact angles on the correlation of the investigated criteria can therefore not be assessed.
The tests only included a single crash cushion with one specific performance lev-el. The extent to which other crash cushions or restraint systems have an influence on the criteria or on the correlation between the criteria cannot be explained.
Likewise, the influence of different vehicle masses or stiffness cannot be derived from the test data. Although lower values would be expected with higher vehicle masses [57].
In line 604 we have included a new paragraph (Future developments):
Due to the limited number of tests, the test matrix would have to be extended eventually with more participating partners (manufactorers of crash cushions). This would allow an assessment of the influence of different impact configurations, con-tainment levels, etc. on the occupant criteria, as well as the correlation between the criteria.
Although THIV or OIV and HIC or a3ms should show a positive correlation, as all these criteria assess the risk of injury to the head, a negative correlation in this context could be observed. In order to evaluate the plausibility of the data, the number of tests should be increased.
Criteria such as HIC, a3ms, etc. have already been proposed in other studies to evaluate occupant safety. Despite this, appropriate ATDs would have to be used in the tests to evaluate these criteria. This would lead to higher costs, which manufacturers of restraint systems would not necessarily accept. The development of new criteria (used in conjunction of existing ones) based on current measurement data at the centre of gravity would thus be a reasonable step towards improving passenger safety.
Even if there are studies on the assessment criteria of road restraint systems, a comprehensive literature study would be recommended in order to process the find-ings to date and highlight all aspects that are either included or missing.
Reviewer 3 Report
Comments and Suggestions for AuthorsSome of the comments are listed as follows:
1. In the comparison of the indicators under different vehicles and different test conditions, it is suggested to add the curves of the time relationship of the indicators, so as to visualize the comparison of the damage results of different vehicles and different working conditions.
2. A lot of text is used to describe the road safety indicators and occupant safety indicators, but the indicators are not clearly categorized. It is suggested that the road safety indicators and occupant safety indicators be divided into two parts, and the parameters and methods used in the calculation of the indicators are explained in simple tables, so as to observe the correlation of the indicators intuitively.
3. In the correlation test between road safety indicators and occupant safety indicators, the sample data selected are only those derived from the above four groups of tests, whether such a small sample size can show the statistical correlation of these two indicators, it is recommended to briefly explain the correlation test method and the credibility of the results.
4. In the discussion section, it is mentioned that the different indicators used for head injury evaluation in the occupant safety standards and road safety standards are negatively correlated, but the reasons for this phenomenon are not explained. It is recommended to analyze in detail the variation of the calculated parameters in the analysis of the results.
Author Response
Some of the comments are listed as follows:
Comment 1: In the comparison of the indicators under different vehicles and different test conditions, it is suggested to add the curves of the time relationship of the indicators, so as to visualize the comparison of the damage results of different vehicles and different working conditions.
Response 1: Thank you for pointing this out. We agree with this comment. Therefore, we have included the test data in the appendix.
In line 282 we have added following text
“Corresponding curves of the time relationships for the criteria are in the appendix B.”
Comment 2: A lot of text is used to describe the road safety indicators and occupant safety indicators, but the indicators are not clearly categorized. It is suggested that the road safety indicators and occupant safety indicators be divided into two parts, and the parameters and methods used in the calculation of the indicators are explained in simple tables, so as to observe the correlation of the indicators intuitively.
Response 2: Thank you for pointing this out. We agree with this comment. Therefore, we divided the chapter into road safety and occupant safety criteria.
We changed the chapter heading (with corresponding sub-chapters) in line 139 and 190 to
3.3. Assessment of road safety criteria
3.4. Assessment of occupant criteria
Further we have summarized the parameters and methods used in the calculation of the indicators in a table and included this in the appendix A in line 634.
Comment 3: In the correlation test between road safety indicators and occupant safety indicators, the sample data selected are only those derived from the above four groups of tests, whether such a small sample size can show the statistical correlation of these two indicators, it is recommended to briefly explain the correlation test method and the credibility of the results.
Response 3: Thank you for pointing this out. We agree with this comment. In the paper it is already described, that the number of experiments is very small. Even though we tried to correlate the criteria. Independent of the sample size, the calculation of the correlation coefficient follows the same formula. We calculated Pearson’s correlation indicated with the “r” in the text, which to our understanding is sufficient for interpretation. Therefore, we have included the information to Pearson in the text which should be sufficient to understand the calculation of the correlation.
In line 386 we have changed following text
“Table 13 summarises the linear regression coefficient r (Pearson’s r) according to the corresponding road safety and occupant safety criteria.”
In line 558 we have also included a chapter on limitations in which we have discussed this issue with the small sample size.
The analysis of the data comprises only four tests. The calculated correlation is therefore based on a small sample size. This may lead to results that cannot be fully explained, as in the case of THIV and OIV, for example. No positive correlation was observed between THIV or OIV and HIC or a3ms head acceleration, but this was ex-pected as these two criteria are used to assess the risk of head injury. This may also be due to the small sample size, although the ASI correlates positively with the HIC and a3ms head acceleration.
Only one test was carried out in each test configuration. Thus, the influence of different impact angles on the correlation of the investigated criteria can therefore not be assessed.
The tests only included a single crash cushion with one specific performance lev-el. The extent to which other crash cushions or restraint systems have an influence on the criteria or on the correlation between the criteria cannot be explained.
Likewise, the influence of different vehicle masses or stiffness cannot be derived from the test data. Although lower values would be expected with higher vehicle masses [57].
Comment 4: In the discussion section, it is mentioned that the different indicators used for head injury evaluation in the occupant safety standards and road safety standards are negatively correlated, but the reasons for this phenomenon are not explained. It is recommended to analyze in detail the variation of the calculated parameters in the analysis of the results.
Response 4: Thank you for pointing this out. We agree with this comment. We referenced and described the literature more precisely. The findings in the literature correlates partially with our findings. At least in the same collision speed group the literature suggests a negative correlation. Including all collision speed groups a positive correlation between OIV and HIC is observed. This is, however, not surprising because HIC is increasing with higher collision speed. Thus, OIV should increase either.
In line 456 we included additional text
Gabauer and Thomson [16] found a negative linear correlation between the OIV and the HIC. Within the analysed tests, at the same collision speed, OIV correlated negative with HIC (25 mph: r=-0,07; 30 mph: -0,61; 35 mph: -0,29). These correlations are comparable with the findings in the current study. In Meng et al. [19] there is no correlation between THIV and HIC15 (r=0.07). The numerical simulation in Li et al. [18], however, yields an exponential correlation of r=0.95 between THIV and HIC15. However, both the speed and the impact angle were varied in this study, which can have a major influence on the values. It was observed, that HIC increased much stronger than THIV. Ziegler et al. [17] conclude that the THIV is actually inappropriate for assessing the head injury risk. Chell et al. [15] also conclude that the THIV does not adequately represent real head impact velocity.
From the literature, only the study by Gabauer and Thomson [16] is comparable with the present results. Gabauer and Thomson were the only authors who analyzed frontal collisions. They found a negative linear correlation between THIV and HIC if impact velocities were clustered. In the other studies (Li et al. [18], Meng et al. [20], Ziegler et al. [17]), different impact angles were considered and the collision velocity was also varied and are therefore not directly comparable.
The reason for the negative correlation between the HIC and the THIV is possibly due to the calculation method. The HIC is calculated directly from the measured accel-erations in the head of the ATD [35] and the THIV is based on the flail space model of Michie [6]. In this model, it is assumed that the occupant collides with a part of the ve-hicle after moved in free flight (“flail”). The THIV corresponds to the speed after this free flight motion.
