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A comparison of the mixed logit and latent class methods for crash severity analysis
The objective of this paper is to investigate the differences between two preferred methods for accommodating individual unobserved heterogeneity, the mixed logit and latent class methods, in exploring the relationship between heavy truck crash severity and its contributing factors. To achieve this, a large sample of crash data on multiple vehicle crashes involving a heavy truck on public roadways in Iowa from 2007 to 2012 was collected. The comparison of the two methods lied on model fit, inferences, and predicted crash severity outcome probabilities. The results suggested a slight superiority of the latent class method i...
Source: Analytic Methods in Accident Research - November 4, 2014 Category: Occupational Health Source Type: research

A two-stage bivariate logistic-Tobit model for the safety analysis of signalized intersections
Publication date: October 2014 Source:Analytic Methods in Accident Research, Volumes 3–4 Author(s): Xuecai Xu , S.C. Wong , Keechoo Choi Crash frequency and crash severity models have explored the factors that influence intersection safety. However, most of these models address the frequency and severity independently, and miss the correlations between crash frequency models at different crash severity levels. We develop a two-stage bivariate logistic-Tobit model of the crash severity and crash risk at different severity levels. The first stage uses a binary logistic model to determine the overall crash severity l...
Source: Analytic Methods in Accident Research - October 31, 2014 Category: Occupational Health Source Type: research

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Publication date: April 2014 Source:Analytic Methods in Accident Research, Volume 2 (Source: Analytic Methods in Accident Research)
Source: Analytic Methods in Accident Research - October 29, 2014 Category: Occupational Health Source Type: research

Modeling safety of highway work zones with random parameters and random effects models
Publication date: January 2014 Source:Analytic Methods in Accident Research, Volume 1 Author(s): Erdong Chen , Andrew P. Tarko This paper presents an investigation of traffic safety in highway work zones using detailed data obtained from the results of a survey of project engineers and existing datasets. The observations were organized in monthly clusters that correspond to individual work zones; and a two-level random parameters negative binomial model that reflected the structure of the observations was estimated. The safety effects of various work zone design and traffic management features were identified, includ...
Source: Analytic Methods in Accident Research - October 12, 2014 Category: Occupational Health Source Type: research

Comparing three commonly used crash severity models on sample size requirements: Multinomial logit, ordered probit and mixed logit models
The objective of this study is therefore to examine the effects of sample size on the three most commonly used crash severity models: multinomial logit, ordered probit and mixed logit models. The study objective is accomplished via a Monte-Carlo approach using simulated and observed crash data. The results of this study are consistent with prior expectations in that small sample sizes significantly affect the development of crash severity models, no matter which type is used. Furthermore, among the three models, the mixed logit model requires the largest sample size, while the ordered probit model requires the lowest sampl...
Source: Analytic Methods in Accident Research - October 12, 2014 Category: Occupational Health Source Type: research

A count data model with endogenous covariates: Formulation and application to roadway crash frequency at intersections
Publication date: January 2014 Source:Analytic Methods in Accident Research, Volume 1 Author(s): Chandra R. Bhat , Kathryn Born , Raghuprasad Sidharthan , Prerna C. Bhat This paper proposes an estimation approach for count data models with endogenous covariates. The maximum approximate composite marginal likelihood inference approach is used to estimate model parameters. The modeling framework is applied to predict crash frequency at urban intersections in Irving, Texas. The sample is drawn from the Texas Department of Transportation (TxDOT) crash incident files for the year 2008. The results highlight the importan...
Source: Analytic Methods in Accident Research - October 12, 2014 Category: Occupational Health Source Type: research

Analyzing different functional forms of the varying weight parameter for finite mixture of negative binomial regression models
This study investigates the effect of different functional forms on the estimation of the weight parameter as well as the group classification of the finite mixture of NB regression models, using crash data collected on rural roadway sections in Indiana. A total of 11 different functional forms for the varying weight parameter were estimated; these functional forms include various combinations of traffic flow and segment length as covariates. The results suggest that the modeling of the weight parameter (which essentially helps in improving the group classification) is generally necessary when using the finite mixture of N...
Source: Analytic Methods in Accident Research - October 12, 2014 Category: Occupational Health Source Type: research

A latent segmentation based generalized ordered logit model to examine factors influencing driver injury severity
Publication date: January 2014 Source:Analytic Methods in Accident Research, Volume 1 Author(s): Shamsunnahar Yasmin , Naveen Eluru , Chandra R. Bhat , Richard Tay This paper formulates and estimates an econometric model, referred to as the latent segmentation based generalized ordered logit (LSGOL) model, for examining driver injury severity. The proposed model probabilistically allocates drivers (involved in a crash) into different injury severity segments based on crash characteristics to recognize that the impacts of exogenous variables on driver injury severity level can vary across drivers based on both obser...
Source: Analytic Methods in Accident Research - October 12, 2014 Category: Occupational Health Source Type: research

Analytic methods in accident research: Methodological frontier and future directions
Publication date: January 2014 Source:Analytic Methods in Accident Research, Volume 1 Author(s): Fred L. Mannering , Chandra R. Bhat The analysis of highway-crash data has long been used as a basis for influencing highway and vehicle designs, as well as directing and implementing a wide variety of regulatory policies aimed at improving safety. And, over time there has been a steady improvement in statistical methodologies that have enabled safety researchers to extract more information from crash databases to guide a wide array of safety design and policy improvements. In spite of the progress made over the years, im...
Source: Analytic Methods in Accident Research - October 12, 2014 Category: Occupational Health Source Type: research

Crash frequency modeling using negative binomial models: An application of generalized estimating equation to longitudinal data
The objective of this study is to explore the effects of temporal correlation in crash frequency models at the highway segment level. In this paper, a negative binomial model has been developed using a generalized estimating equation (GEE) procedure that incorporates the temporal correlations amongst yearly crash counts. The longitudinal model employs an autoregressive correlation structure to compare to the more traditional NB model, which uses a Maximum Likelihood Estimation (MLE) method that cannot accommodate temporal correlations. The GEE model with temporal correlation was found to be superior compared to the MLE mod...
Source: Analytic Methods in Accident Research - October 12, 2014 Category: Occupational Health Source Type: research

Crash frequency modeling for signalized intersections in a high-density urban road network
Publication date: April 2014 Source:Analytic Methods in Accident Research, Volume 2 Author(s): Kun Xie , Xuesong Wang , Kaan Ozbay , Hong Yang Conventional crash frequency models rely on an assumption of independence among observed crashes. However, this assumption is frequently proved false by spatially related crash observations, particularly for intersection crashes observed in high-density road networks. Crash frequency models that ignore the hierarchy and spatial correlation of closely spaced intersections can lead to biased estimations. As a follow-up to our previous paper (Xie et al., 2013), this study aims ...
Source: Analytic Methods in Accident Research - October 12, 2014 Category: Occupational Health Source Type: research

A latent class analysis of single-vehicle motorcycle crash severity outcomes
Publication date: April 2014 Source:Analytic Methods in Accident Research, Volume 2 Author(s): Mohammad Saad Shaheed , Konstantina Gkritza Unobserved heterogeneity has been recognized as a critical issue in traffic safety research that has not been completely addressed or often overlooked, and can lead to biased estimates and incorrect inferences if inappropriate methods are used. This paper uses a latent class approach to investigate the factors that affect crash severity outcomes in single-vehicle motorcycle crashes. Motorcycle crash data from 2001 to 2008 in Iowa were collected with a total of 3644 single-vehicle ...
Source: Analytic Methods in Accident Research - October 12, 2014 Category: Occupational Health Source Type: research

Comparison of factors affecting injury severity in angle collisions by fault status using a random parameters bivariate ordered probit model
Publication date: April 2014 Source:Analytic Methods in Accident Research, Volume 2 Author(s): Brendan J. Russo , Peter T. Savolainen , William H. Schneider IV , Panagiotis Ch. Anastasopoulos The extant traffic safety research literature includes numerous examples of studies that assess those factors affecting the degree of injury sustained by crash-involved motor vehicle occupants. One important methodological concern in such work is the potential correlation in injury outcomes among occupants involved in the same crash, which may be due to common unobserved factors affecting such occupants. A second concern is un...
Source: Analytic Methods in Accident Research - October 12, 2014 Category: Occupational Health Source Type: research

A heterogeneity-in-means count model for evaluating the effects of interchange type on heterogeneous influences of interstate geometrics on crash frequencies
Publication date: April 2014 Source:Analytic Methods in Accident Research, Volume 2 Author(s): Narayan Venkataraman , Venky Shankar , Gudmundur F. Ulfarsson , Damian Deptuch This paper presents a heterogeneity-in-means, random-parameter negative binomial (HMRPNB) model of interchange type effects on interchange and non-interchange segment crash frequencies. For non-interchange segments, upstream and downstream type combinations were evaluated. Eight interchange types, namely, directional, semidirectional, clover, partclover, diamond, part diamond, single-point-urban-interchange (SPUI), and other were studied on the...
Source: Analytic Methods in Accident Research - October 12, 2014 Category: Occupational Health Source Type: research

Incorporating spatial dependence in simultaneously modeling crash frequency and severity
Publication date: April 2014 Source:Analytic Methods in Accident Research, Volume 2 Author(s): Yu-Chiun Chiou , Chiang Fu , Hsieh Chih-Wei Estimation results obtained by models of crash frequency and severity without considering spatial dependence effects may lead to biased estimates and mis-specification of the risk factors in accident analysis. The solution developed in this study is a modification of the previously proposed multinomial-generalized Poisson with error-components (EMGP) model. Two spatial EMGP models, spatial error-EMGP and spatial exogenous-EMGP, are proposed to accommodate alternative spatial depe...
Source: Analytic Methods in Accident Research - October 12, 2014 Category: Occupational Health Source Type: research