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A flexible discrete density random parameters model for count data: Embracing unobserved heterogeneity in highway safety analysis
Publication date: December 2018Source: Analytic Methods in Accident Research, Volume 20Author(s): Shahram HeydariAbstractIn traffic safety studies, there are almost inevitable concerns about unobserved heterogeneity. As a feasible alternative to current methods, this article proposes a novel crash count model that can address asymmetry and multimodality in the data. Specifically, a Bayesian random parameters model with flexible discrete densities for the regression coefficients is developed, employing a Dirichlet process prior. The approach is illustrated on the Ontario Highway 401, which is one of the busiest North Americ...
Source: Analytic Methods in Accident Research - November 5, 2018 Category: Accident Prevention Source Type: research

Investigating varying effect of road-level factors on crash frequency across regions: A Bayesian hierarchical random parameter modeling approach
This study aims to quantitatively examine the variations in effect of road-level factors on crash frequency across different regions. Treating the hierarchical structure existing in the crash data that road entity nested within the geographic region, a hierarchical random parameter model, which allows the coefficients of road-level variables to vary with regions, is proposed. A Poisson lognormal model and a hierarchical random intercept model are also built for the purpose of comparison. A specific roadway facility type, urban two-lane two-way roadway segments in Florida, with crash and road level data including traffic vo...
Source: Analytic Methods in Accident Research - October 20, 2018 Category: Accident Prevention Source Type: research

Non-decreasing threshold variances in mixed generalized ordered response models: A negative correlations approach to variance reduction
This study highlights a potential limitation of these models, as applied in most empirical research, that the variances of the random thresholds are implicitly assumed to be in a non-decreasing order. This restriction is unnecessary and can lead to difficulty in estimation of random parameters in higher order thresholds. In this study, we investigate the use of negative correlations between random parameters as a variance reduction technique to relax the property of non-decreasing variances of thresholds in MGOR models. To this end, a simulation-based approach was used (where multiple datasets were simulated assuming a kno...
Source: Analytic Methods in Accident Research - October 9, 2018 Category: Accident Prevention Source Type: research

Analysis of accident injury-severity outcomes: The zero-inflated hierarchical ordered probit model with correlated disturbances
Publication date: December 2018Source: Analytic Methods in Accident Research, Volume 20Author(s): Grigorios Fountas, Panagiotis Ch. AnastasopoulosAbstractIn accident injury-severity analysis, an inherent limitation of the traditional ordered probit approach arises from the a priori consideration of a homogeneous source for the accidents that result in a no-injury (or zero-injury) outcome. Conceptually, no-injury accidents may be subject to the effect of two underlying injury-severity states, which are more likely to be observed in accident datasets with excessive amounts of no-injury accident observations. To account for t...
Source: Analytic Methods in Accident Research - October 5, 2018 Category: Accident Prevention Source Type: research

Evaluating temporal variability of exogenous variable impacts over 25 years: An application of scaled generalized ordered logit model for driver injury severity
Publication date: December 2018Source: Analytic Methods in Accident Research, Volume 20Author(s): Robert Marcoux, Shamsunnahar Yasmin, Naveen Eluru, Moshiur RahmanAbstractThe current study undertakes a unique research effort to quantify the impact of various exogenous factors on crash severity over time. Specifically, we examine if over time, the impact of exogenous variables has changed and if so what is the magnitude of the change. The research contributes to driver injury severity analysis both methodologically and empirically by proposing a framework that addresses the challenges associated with pooled (or pseudo-panel...
Source: Analytic Methods in Accident Research - October 4, 2018 Category: Accident Prevention Source Type: research

Exploring driver injury severity patterns and causes in low visibility related single-vehicle crashes using a finite mixture random parameters model
This study provides an insightful understanding of the impacts of these variables on driver injury severity outcomes in low visibility related crashes, and a beneficial reference for developing countermeasures and strategies to mitigate driver injury severities under these conditions. (Source: Analytic Methods in Accident Research)
Source: Analytic Methods in Accident Research - September 7, 2018 Category: Accident Prevention Source Type: research

A comprehensive joint econometric model of motor vehicle crashes arising from multiple sources of risk
This study first postulates, and then demonstrates empirically, that crash occurrence may be more complex than can be adequately captured by a single equation regression model. The total crash count recorded at a transport network location (e.g. road segment) may arise from multiple simultaneous and inter-dependent sources of risk, rather than one. Each of these sources may uniquely contribute to the total observed crash count. For instance, a site’s crash occurrence may be dominated by contributions from driver behaviour issues (e.g. speeding, impaired driving), while another site’s crashes might arise predominately f...
Source: Analytic Methods in Accident Research - July 10, 2018 Category: Accident Prevention Source Type: research

Analysis of vehicle accident-injury severities: A comparison of segment- versus accident-based latent class ordered probit models with class-probability functions
Publication date: June 2018Source: Analytic Methods in Accident Research, Volume 18Author(s): Grigorios Fountas, Panagiotis Ch. Anastasopoulos, Fred L. ManneringAbstractUsing information from 1990 single-vehicle accidents that occurred between 2011 and 2013 in the state of Washington, the injury severity level of the most severely injured vehicle occupant is studied using two latent class modeling approaches: segment-based and accident-based latent class ordered probit model with class-probability functions. The segment-based latent class ordered probit framework allows explanatory parameters to vary across unobserved grou...
Source: Analytic Methods in Accident Research - July 10, 2018 Category: Accident Prevention Source Type: research

Developing a Random Parameters Negative Binomial-Lindley Model to analyze highly over-dispersed crash count data
Publication date: June 2018Source: Analytic Methods in Accident Research, Volume 18Author(s): Mohammad Razaur Rahman Shaon, Xiao Qin, Mohammadali Shirazi, Dominique Lord, Srinivas Reddy GeedipallyAbstractThe existence of preponderant zero crash sites and/or sites with large crash counts can present challenges during the statistical analysis of crash count data. Additionally, unobserved heterogeneity in crash data due to the absence of important variables could negatively impact the estimated model parameters. The traditional negative binomial (NB) model with fixed parameters might not adequately handle highly over-disperse...
Source: Analytic Methods in Accident Research - July 10, 2018 Category: Accident Prevention Source Type: research

A joint framework for static and real-time crash risk analysis
Publication date: June 2018Source: Analytic Methods in Accident Research, Volume 18Author(s): Shamsunnahar Yasmin, Naveen Eluru, Ling Wang, Mohamed A. Abdel-AtyAbstractThe current research effort bridges the gap between traditional crash risk and real-time crash risk models by developing a joint model that accommodates for both dimensions in developing crash risk analysis models. Specifically, we develop a joint reactive and proactive crash modeling framework by coupling the monthly crash risk and real-time crash risk in a unified econometric framework for a microscopic analysis unit. In the joint modeling approach, we pro...
Source: Analytic Methods in Accident Research - July 10, 2018 Category: Accident Prevention Source Type: research

Analysis of accident injury-severities using a correlated random parameters ordered probit approach with time variant covariates
Publication date: June 2018Source: Analytic Methods in Accident Research, Volume 18Author(s): Grigorios Fountas, Panagiotis Ch. Anastasopoulos, Mohamed Abdel-AtyAbstractThis paper employs a correlated random parameters ordered probit modeling framework to explore time-variant and time-invariant factors affecting injury-severity outcomes in single-vehicle accidents. The proposed approach extends traditional random parameters modeling, by accounting for possible correlations among the random parameters. On the basis of an unrestricted covariance matrix for the random parameters, the proposed framework can capture the combine...
Source: Analytic Methods in Accident Research - July 10, 2018 Category: Accident Prevention Source Type: research

Developing a grouped random parameters multivariate spatial model to explore zonal effects for segment and intersection crash modeling
Publication date: September 2018Source: Analytic Methods in Accident Research, Volume 19Author(s): Qing Cai, Mohamed Abdel-Aty, Jaeyoung Lee, Ling Wang, Xuesong WangAbstractIt is acknowledged that crash occurrence on segments and intersections could be affected by multilevel factors. Omission of important explanatory variables could result in biased and inconsistent parameter estimates. This paper contributes to the literature by examining the zonal effects which are always excluded or ignored in traffic safety research for segments and intersections. A grouped random parameters multivariate spatial model is proposed to id...
Source: Analytic Methods in Accident Research - July 10, 2018 Category: Accident Prevention Source Type: research

A joint econometric approach for modeling crash counts by collision type
Publication date: September 2018Source: Analytic Methods in Accident Research, Volume 19Author(s): Tanmoy Bhowmik, Shamsunnahar Yasmin, Naveen EluruAbstractIn recent years, there is growing recognition that common unobserved factors that influence crash frequency by one attribute level are also likely to influence crash frequency by other attribute levels. The most common approach employed to address the potential unobserved heterogeneity in safety literature is the development of multivariate crash frequency models. The current study proposes an alternative joint econometric framework to accommodate for the presence of un...
Source: Analytic Methods in Accident Research - July 10, 2018 Category: Accident Prevention Source Type: research

Benchmarking regions using a heteroskedastic grouped random parameters model with heterogeneity in mean and variance: Applications to grade crossing safety analysis
This study provides valuable guidelines to Canadian transportation authorities, revealing important underlying crash mechanisms at highway railway grade crossings in Canada. (Source: Analytic Methods in Accident Research)
Source: Analytic Methods in Accident Research - July 10, 2018 Category: Accident Prevention Source Type: research

A mixed grouped response ordered logit count model framework
Publication date: September 2018Source: Analytic Methods in Accident Research, Volume 19Author(s): Shamsunnahar Yasmin, Naveen EluruAbstractThe study proposes and estimates a new econometric framework for analysing crash count events labeled as the Mixed Grouped Response Ordered Logit Count model. The proposed framework relates the crash count propensity to the observed counts directly while also accommodating for heteroscedasticity and unobserved heterogeneity. The proposed model is demonstrated by using Traffic Analysis Zone level bicycle crash count data for the Island of Montreal. The model framework employs a comprehe...
Source: Analytic Methods in Accident Research - July 10, 2018 Category: Accident Prevention Source Type: research