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留学生论文网:Accident Analysis and Prevention:Model

Accident Analysis and Prevention 40 (2008) 76–88
Modeling left-turn crash occurrence at signalized intersections by conflicting patterns
Department of Civil & Environmental Engineering, University of Central Florida,
Orlando, FL 32816-2450, United States
Received 14 October 2006; received in revised form 26 February 2007; accepted 20 April 2007
In order to better understand the underlying crash mechanisms, left-turn crashes occurring at 197 four-legged signalized intersections over 6years were classified into nine patterns based on vehicle maneuvers and then were assigned to intersection approaches. Crash frequency of eachpatternwas modeled at the approach level by mainly using Generalized Estimating Equations (GEE) with the 留学生论文网Negative Binomial as the link functionto account for the correlation among the crash data. GEE with a binomial logit link function was also applied for patterns with fewer crashes.The Cumulative Residuals test shows that, for correlated left-turn crashes, GEE models usually outperformed basic Negative Binomial models.The estimation results show that there are obvious differences in the factors that cause the occurrence of different left-turn collision patterns. Forexample, for each pattern, the traffic flows to which the colliding vehicles belong are identified to be significant. The width of the crossing distance(represented by the number of through lanes on the opposing approach of the left-turning traffic) is associated with more left-turn traffic collidingwith opposing through traffic (Pattern 5), but with less left-turning traffic colliding with near-side crossing through traffic (Pattern 8). The safetyeffectiveness of the left-turning signal is not consistent for different crash patterns; “protected” phasing is correlated with fewer Pattern 5 crashes,but with more Pattern 8 crashes. The study indicates that in order to develop efficient countermeasures for left-turn crashes and improve safety atsignalized intersections, left-turn crashes should be considered in different patterns.
Keywords: Signalized intersection; Left-turn crashes; Conflicting patterns; Approach level model; Negative Binomial; Generalized Estimating Equations
1. Introduction
Analyzing left-turning traffic is crucial for improving intersectionoperation and safety. This traffic may collide with manyother traffic flows at signalized intersections, e.g., with leftturningtraffic from the same approach or from the differentapproaches, and with through traffic from other approaches;therefore, left-turn crashes have many distinct conflicting patternsin vehicle maneuvers before collisions. Left-turn crashesare among the most frequently occurring collision types; basedon the crash history of 1531 signalized intersections in the stateof Florida, left-turn crashes rank third, following rear-end andangle crashes, and represent 16% of all intersection reportedcrashes (Abdel-Aty et al., 2005).At signalized intersections, differences exist in traffic volumes,site geometry, and signal operations, as well as safety∗ Corresponding author. Tel.: +1 407 8235657; fax: +1 407 8234676.E-mail address: (M. Abdel-Aty).

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