A simulation-based empirical bayes approach: Incorporating unobserved heterogeneity in the before-after evaluation of engineering treatments

Tahir, Hassan Bin; Boyle, Linda Ng; Yasmin, Shamsunnahar; King, Mark

doi:10.1016/j.aap.2021.106527

Cited by 9 publications

(3 citation statements)

References 26 publications

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“…Third, the proposed methodology is relatively simple and could realistically be applied by practitioners in real-world projects. In road safety literature, more advanced before-after methodologies have been proposed, for example accounting for unobserved heterogeneity (Tahir et al, 2022) but, for realistic transferability from research to practical applications, the methodology must be compatible with the limited time and resources available for this kind of urban design interventions which, as in the present case study, have relatively low costs. The proposed methodology is based on theoretically-sound choices on the surrogate measure of safety to identify traffic conflicts and on the distribution used to model the probabilistic relationship between conflicts and crashes (as extensively discussed in Section 2), but it is also easily applicable: e.g.,…”

Section: Main Features Of the Proposed Methodologymentioning

confidence: 99%

Before-after safety analysis of a shared space implementation

Orsini

Batista

Friedrich

et al. 2023

Case Studies on Transport Policy

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Section: Main Features Of the Proposed Methodologymentioning

confidence: 99%

Before-after safety analysis of a shared space implementation

Orsini

Batista

Friedrich

et al. 2023

Case Studies on Transport Policy

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“…Since they are basic safety requirements, the resultant and vertical accelerations of P1.5 dummy's chest in dynamic tests are taken as the object for quantitative research. As to the issue, it is more scientific and objective to explore the current research based on experimental validations than pure computer simulation, for the quality of computer simulation depends on algorithms to a great extent [35,36,37]. Furthermore, simulation itself needs experimental validation to check its validity and correctness [38,39].…”

Section: Introductionmentioning

confidence: 99%

Analysis of the Effect of Infant Carrier’s Webbing Tension on 18-month-old Child Occupant’s Chest Accelerations in Frontal Crash Accidents Based on Experimental Validations

2023

JERT

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Infant carriers play an important role in protecting child occupants from severe injuries caused by collisions, but the tension of harness webbing cannot be controlled properly most of the time. Infant carrier’s user manual or instruction generally contains little information about the extent to which the adjusting belt should be pulled to cause the necessary webbing tension, and it is often neglected that the infants should be restrained securely. In order to improve public awareness, it is important to ascertain the effect of infant carrier’s webbing tension on the occupant’s chest accelerations. A testing scheme including 12 dynamic tests was devised and conducted, and test conditions were controlled strictly to ensure the accuracy and objectivity of results. P1.5 dummy’s resultant and vertical chest accelerations were collected and analyzed. Both ISOFIX installation and seat belt installation methods were taken into consideration without lack of generality. Sled’s accelerations and velocities were set and acquired, which constituted the fundamental testing conditions of dynamic tests and ensured the repeatability and reliability of tests. Furthermore, dummy’s chest acceleration pulses were monitored and recorded, and the data were evaluated in accordance with criteria defined in relevant technical standards. The dummy’s chest accelerations were classified into 2 groups according to child restraint systems’ installation methods, i.e., the ISOFIX group and the seat belt group. In each group, both resultant chest acceleration and vertical chest acceleration were involved. Universal phenomena were displayed in all the tests, and the larger the tensile forces were, the lower the chest accelerations were in tests. Based on experimental validations, the relation between webbing’s tensions and chest accelerations in frontal crash accidents was verified. Furthermore, suggestions were made about adjusting the webbing tension and the proper use of infant carriers.

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“…For more examples of unobserved heterogeneity, please refer to Mannering et al (2016) [14]. If unobserved heterogeneity is overlooked, and the effects of explanatory variables are restricted to be the same across all observations, the model will be mis-specified and the estimated parameters are likely to be biased and inefficient, which could, in turn, lead to erroneous inferences [15][16][17][18]. Of the various techniques to account for unobserved heterogeneity, the so-called random parameters approach has been widely used [19][20][21].…”

Section: Introductionmentioning

confidence: 99%

Joint Analysis of Crash Frequency by Severity Based on a Random Parameters Approach

Chen,

Xu,

2023

Sustainability

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Unobserved heterogeneity is a major challenge in estimating reliable road safety models. The random parameters approach has been proven to be an effective way to account for unobserved heterogeneity but has rarely been used for crash frequency by severity level. In this paper, a fixed parameters model, a basic random parameters model, and an improved random parameters model, allowing for heterogeneity in the means and correlation of random parameters, are estimated and comparatively evaluated. To quantitatively analyze the impact of explanatory variables on the crash frequency of various severity levels, the calculating method of marginal effects for estimated models is proposed. The results indicate that (1) the basic random parameters model statistically outperforms the fixed parameters model, and the statistical fit can be further improved by introducing heterogeneous means and correlation of random parameters; (2) for the predictive performance, the basic random parameters model is more accurate than the fixed parameters model, and the improved random parameters model can further reduce the mean error, mean absolute error, and root mean square error by 40–100%, 3.7–8.3%, and 7.6–8.9%, respectively; (3) ignoring the unobserved heterogeneity or neglecting the heterogeneity in the means and correlation of random parameters may result in biased safety inferences, and the maximum bias of marginal effects can easily exceed 100 percent; and (4) the safety effects of explanatory variables are thoroughly discussed and the potential safety countermeasures are provided. The random parameters approach and the method for calculating marginal effects proposed in this study are expected to provide a new methodological alternative for the joint analysis of crash frequency by severity and should be helpful in uncovering the mechanism of crash occurrence and the resulting injury severity accurately.

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A simulation-based empirical bayes approach: Incorporating unobserved heterogeneity in the before-after evaluation of engineering treatments

Cited by 9 publications

References 26 publications

Before-after safety analysis of a shared space implementation

Before-after safety analysis of a shared space implementation

Analysis of the Effect of Infant Carrier’s Webbing Tension on 18-month-old Child Occupant’s Chest Accelerations in Frontal Crash Accidents Based on Experimental Validations

Joint Analysis of Crash Frequency by Severity Based on a Random Parameters Approach

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