Modeling accident frequencies as zero-altered probability processes

An empirical inquiry

Venkataraman Shankar, J. Milton, F. Mannering

Research output: Contribution to journalArticle

223 Citations (Scopus)

Abstract

This paper presents an empirical inquiry into the applicability of zero-altered counting processes to roadway section accident frequencies. The intent of such a counting process is to distinguish sections of roadway that are truly safe (near zero-accident likelihood) from those that are unsafe but happen to have zero accidents observed during the period of observation (e.g. one year). Traditional applications of Poisson and negative binomial accident frequency models do not account for this distinction and thus can produce biased coefficient estimates because of the preponderance of zero-accident observations. Zero-altered probability processes such as the zero-inflated Poisson (ZIP) and zero-inflated negative binomial (ZINB) distributions are examined and proposed for accident frequencies by roadway functional class and geographic location. The findings show that the ZIP structure models are promising and have great flexibility in uncovering processes affecting accident frequencies on roadway sections observed with zero accidents and those with observed accident occurrences. This flexibility allows highway engineers to better isolate design factors that contribute to accident occurrence and also provides additional insight into variables that determine the relative accident likelihoods of safe versus unsafe roadways. The generic nature of the models and the relatively good power of the Vuong specification test used in the non-nested hypotheses of model specifications offers roadway designers the potential to develop a global family of models for accident frequency prediction that can be embedded in a larger safety management system.

Original languageEnglish (US)
Pages (from-to)829-837
Number of pages9
JournalAccident Analysis and Prevention
Volume29
Issue number6
DOIs
StatePublished - Jan 1 1997

Fingerprint

accident frequency
Accidents
accident
flexibility
engineer
Binomial Distribution
Specifications
Safety Management
Geographic Locations
Model structures

All Science Journal Classification (ASJC) codes

  • Human Factors and Ergonomics
  • Safety, Risk, Reliability and Quality
  • Public Health, Environmental and Occupational Health
  • Law

Cite this

Shankar, Venkataraman ; Milton, J. ; Mannering, F. / Modeling accident frequencies as zero-altered probability processes : An empirical inquiry. In: Accident Analysis and Prevention. 1997 ; Vol. 29, No. 6. pp. 829-837.
@article{9f365e139df3474e9250f91dd912a2ae,
title = "Modeling accident frequencies as zero-altered probability processes: An empirical inquiry",
abstract = "This paper presents an empirical inquiry into the applicability of zero-altered counting processes to roadway section accident frequencies. The intent of such a counting process is to distinguish sections of roadway that are truly safe (near zero-accident likelihood) from those that are unsafe but happen to have zero accidents observed during the period of observation (e.g. one year). Traditional applications of Poisson and negative binomial accident frequency models do not account for this distinction and thus can produce biased coefficient estimates because of the preponderance of zero-accident observations. Zero-altered probability processes such as the zero-inflated Poisson (ZIP) and zero-inflated negative binomial (ZINB) distributions are examined and proposed for accident frequencies by roadway functional class and geographic location. The findings show that the ZIP structure models are promising and have great flexibility in uncovering processes affecting accident frequencies on roadway sections observed with zero accidents and those with observed accident occurrences. This flexibility allows highway engineers to better isolate design factors that contribute to accident occurrence and also provides additional insight into variables that determine the relative accident likelihoods of safe versus unsafe roadways. The generic nature of the models and the relatively good power of the Vuong specification test used in the non-nested hypotheses of model specifications offers roadway designers the potential to develop a global family of models for accident frequency prediction that can be embedded in a larger safety management system.",
author = "Venkataraman Shankar and J. Milton and F. Mannering",
year = "1997",
month = "1",
day = "1",
doi = "10.1016/S0001-4575(97)00052-3",
language = "English (US)",
volume = "29",
pages = "829--837",
journal = "Accident Analysis and Prevention",
issn = "0001-4575",
publisher = "Elsevier Limited",
number = "6",

}

Modeling accident frequencies as zero-altered probability processes : An empirical inquiry. / Shankar, Venkataraman; Milton, J.; Mannering, F.

In: Accident Analysis and Prevention, Vol. 29, No. 6, 01.01.1997, p. 829-837.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Modeling accident frequencies as zero-altered probability processes

T2 - An empirical inquiry

AU - Shankar, Venkataraman

AU - Milton, J.

AU - Mannering, F.

PY - 1997/1/1

Y1 - 1997/1/1

N2 - This paper presents an empirical inquiry into the applicability of zero-altered counting processes to roadway section accident frequencies. The intent of such a counting process is to distinguish sections of roadway that are truly safe (near zero-accident likelihood) from those that are unsafe but happen to have zero accidents observed during the period of observation (e.g. one year). Traditional applications of Poisson and negative binomial accident frequency models do not account for this distinction and thus can produce biased coefficient estimates because of the preponderance of zero-accident observations. Zero-altered probability processes such as the zero-inflated Poisson (ZIP) and zero-inflated negative binomial (ZINB) distributions are examined and proposed for accident frequencies by roadway functional class and geographic location. The findings show that the ZIP structure models are promising and have great flexibility in uncovering processes affecting accident frequencies on roadway sections observed with zero accidents and those with observed accident occurrences. This flexibility allows highway engineers to better isolate design factors that contribute to accident occurrence and also provides additional insight into variables that determine the relative accident likelihoods of safe versus unsafe roadways. The generic nature of the models and the relatively good power of the Vuong specification test used in the non-nested hypotheses of model specifications offers roadway designers the potential to develop a global family of models for accident frequency prediction that can be embedded in a larger safety management system.

AB - This paper presents an empirical inquiry into the applicability of zero-altered counting processes to roadway section accident frequencies. The intent of such a counting process is to distinguish sections of roadway that are truly safe (near zero-accident likelihood) from those that are unsafe but happen to have zero accidents observed during the period of observation (e.g. one year). Traditional applications of Poisson and negative binomial accident frequency models do not account for this distinction and thus can produce biased coefficient estimates because of the preponderance of zero-accident observations. Zero-altered probability processes such as the zero-inflated Poisson (ZIP) and zero-inflated negative binomial (ZINB) distributions are examined and proposed for accident frequencies by roadway functional class and geographic location. The findings show that the ZIP structure models are promising and have great flexibility in uncovering processes affecting accident frequencies on roadway sections observed with zero accidents and those with observed accident occurrences. This flexibility allows highway engineers to better isolate design factors that contribute to accident occurrence and also provides additional insight into variables that determine the relative accident likelihoods of safe versus unsafe roadways. The generic nature of the models and the relatively good power of the Vuong specification test used in the non-nested hypotheses of model specifications offers roadway designers the potential to develop a global family of models for accident frequency prediction that can be embedded in a larger safety management system.

UR - http://www.scopus.com/inward/record.url?scp=0031279422&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0031279422&partnerID=8YFLogxK

U2 - 10.1016/S0001-4575(97)00052-3

DO - 10.1016/S0001-4575(97)00052-3

M3 - Article

VL - 29

SP - 829

EP - 837

JO - Accident Analysis and Prevention

JF - Accident Analysis and Prevention

SN - 0001-4575

IS - 6

ER -