title: Investigation on the role of traffic volume in accidents on urban highways.
abstract: BACKGROUND
  Roadway safety is a major concern for the general public and public agencies, as roadway crashes claim many lives and cause substantial economic loss each year. In Iran, a large number of vehicles are involved in road accidents each year, which cause many deaths and extensive property damage; such accidents are among the major causes of death and disability in the country.
  
  
  METHODS
  To reduce roadway accidents, the factors that affect the occurrence and severity of accidents should be scrutinized to prevent or reduce their effect. The method that many researchers have adopted to determine the effective parameters surrounding road accidents in recent years is through statistical modeling of accidents. In this article, the role of different kinds of vehicles in traffic flow are investigated separately in terms of the likelihood of crashes on urban highways, and the vehicles are divided into three groups: passenger cars, heavy vehicles, and light non-passenger car vehicles. Poisson and negative binomial (NB) regression models were applied to model the accidents in this research, which were categorized into two groups: no injury (property damage only) accidents and more severe (injury and fatal) accidents.
  
  
  RESULTS
  Ultimately, we conclude that light non-passenger car vehicles (i.e., taxis and motorcycles) play the largest role in the occurrence of crashes on urban highways for both types of accidents.
authors.affiliation: Department of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran. esmaeel@ayati.co.uk
authors.forename: Esmaeel
authors.initials: E
authors.lastname: Ayati
authors.forename: Ehsan
authors.initials: E
authors.lastname: Abbasi
mesh_terms: D000063:Accidents, Traffic / Q000706:statistics & numerical data; D001334:Automobile Driving / Q000706:statistics & numerical data; D002947:Cities; D007492:Iran; D015233:Models, Statistical