Evaluating the safety impacts of the number and arrangement of lanes on freeway exit ramps

Chen, Huey tsyh; Liu, Pan; Lü, Jian; Behzadi, Bijan

doi:10.1016/j.aap.2009.01.016

Cited by 76 publications

(51 citation statements)

References 3 publications

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“…In every group, there is a significant increase in both total and FI crashes, with an increase in AADT, as more crashes always occur at high traffic volumes, as in congested situations. This is consistent with other studies (e.g., Pilko et al, 2007;Chen, et al, 2009). There is also an increase in crashes with the increase of the inside (left) shoulder width.…”

Section: Data and Modelssupporting

confidence: 82%

Development of Safety Performance Functions for SafetyAnalyst Applications in Florida

Lu¹

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During the time of my doctoral study at Florida International University, he helped me become a professional, responsible, and confident person. Dr. Gan's influence on my life has spanned many levels, at times as a professor, at other times, like a caring father.Dr. Gan taught me invaluable wisdom and problem-solving skills, both of which have been of great benefit to me during my studies, and will certainly continue to do so as I enter the engineering profession. He even took time out of his busy schedule to show me how to write professionally, from emails to technical papers. With Dr. Gan's help, I received many university, state, and international honors and awards. He has shown me that nothing is impossible if I simply believe and try my best. I am deeply honored to have been one of Dr. Gan's students. SafetyAnalyst implements the empirical Bayes (EB) method, which requires the use of Safety Performance Functions (SPFs). The system is equipped with a set of national default SPFs, and the software calibrates the default SPFs to represent the agency's safety performance. However, it is recommended that agencies generate agency-specific SPFs whenever possible. Many investigators support the view that the agency-specific SPFs represent the agency data better than the national default SPFs calibrated to agency data. Furthermore, it is believed that the crash trends in Florida are different from the states whose data were used to develop the national default SPFs.In this dissertation, Florida-specific SPFs were developed using the 2008 Roadway Characteristics Inventory (RCI) data and crash and traffic data from [2007][2008][2009][2010] for both total and fatal and injury (FI) crashes. The data were randomly divided into two sets, one for calibration (70% of the data) and another for validation (30% of the data). The negative binomial (NB) model was used to develop the Florida-specific SPFs vii for each of the subtypes of roadway segments, intersections and ramps, using the calibration data. Statistical goodness-of-fit tests were performed on the calibrated models, which were then validated using the validation data set. The results were compared in order to assess the transferability of the Florida-specific SPF models.The default SafetyAnalyst SPFs were calibrated to Florida data by adjusting the national default SPFs with local calibration factors.The performance of the Florida-specific SPFs and SafetyAnalyst default SPFs calibrated to Florida data were then compared using a number of methods, including visual plots and statistical goodness-of-fit tests. The plots of SPFs against the observed crash data were used to compare the prediction performance of the two models. Three goodness-of-fit tests,represented by the mean absolute deviance (MAD), the mean square prediction error (MSPE), and Freeman-Tukey R 2 (R 2 FT ), were also used for comparison in order to identify the better-fitting model. The results showed that Florida-specific SPFs yielded better prediction performance than the national default SPFs calibr...

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Section: Data and Modelssupporting

confidence: 82%

Development of Safety Performance Functions for SafetyAnalyst Applications in Florida

Lu¹

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“…In previous studies, a section with 457.5 m (1500 ft) in the upstream and 304.8 m (1000 ft) in the downstream was considered as the influencing area of an exit ramp (Chen et al, 2009;Liu et al, 2010). On the Guangshen freeway, the message signs for exits are usually posted 500 m upstream of the exits.…”

Section: Datamentioning

confidence: 99%

“…In most of the previous crash prediction models, crash counts were usually aggregated over several years and the average crash count per year was considered the response variable (Bauer and Harwood, 1998;Bared et al, 1999;McCartt et al, 2004;Chen et al, 2009;Lord and Mannering, 2010;Liu et al, 2010;Washington et al, 2010). The reason for this is to reduce the random variation in the yearly crash data.…”

Section: Introductionmentioning

confidence: 99%

Application of generalized estimating equations for crash frequency modeling with temporal correlation

Liu

et al. 2014

J. Zhejiang Univ. Sci. A

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Traditional crash frequency modeling uses crash frequency data averaged across multiple years. When data size is small, crash data in each year are used in the modeling to extend the size of the samples. The extension of sample size could create a temporal correlation among crash frequencies of the different years, which could affect the modeling accuracy. The primary objective of this study is to evaluate the application of the generalized estimating equation (GEE) procedures to account for the temporal correlation in the longitudinal crash frequency data. Four-year crash data at exit ramps on a freeway in China were collected for modeling. Based on the same data, traditional generalized linear models (GLMs) were estimated for model comparison. Results showed that traditional GLM underestimated the standard errors of coefficients for explanatory variables. The GEE procedure with an exchangeable correlation structure successively captured the temporal correlation among the crash frequencies of the different years. The GLM with GEE outperformed the traditional GLM in providing a good fit for the crash frequency data. Results of this study can help researchers better understand how various factors affect the crash frequencies at freeway divergent areas and propose effective countermeasures.

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“…In addition to the studies above, there were also researches on diverging segments' safety. Some researchers explored the contributing factors to crashes at freeway diverging locations [7][8], they discovered that AADT, lane-type configuration and speed are always tend to increase the severity of crashes at freeway diverging areas. The operating speed of diverging segments were also been studied [9][10], and linear regression model were adopted to predict the speed of diverging area.…”

Section: Introductionmentioning

confidence: 99%

Speed-consistency Based Safety Evaluation for Freeway Diverging Segments

et al. 2017

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Abstract. Diverging segments are potential bottlenecks because of frequent lane change and deceleration maneuvers. Speed study has been proven to be an effective way to understand the safety performance of diverging segments. T his paper addresses the safety level of diverging segments in terms of speed consistency. Speed data is extracted by T racker based on aerial video imager collected at the diverging segment of MaQun interchange of G42 in Nanjing, China. The operating speed of vehicles is assumed to follow the Linear Regression Model with two explanatory variables-initial velocity and running distance, and the estimated operating speed is amended un der actual traffic conditions. Furthermore, average speed, speed difference and the coefficient of variation are used as safety indicators to establish the speed evaluation criteria. Last but not the least, based on vague set of material-units, the safety level of diverging segments in terms of the velocity arrives at level III, which means that consideration must be given about the safety of diverging segments. T he proposed methodology can be used to estimate the safety of diverging segments.

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Evaluating the safety impacts of the number and arrangement of lanes on freeway exit ramps

Cited by 76 publications

References 3 publications

Development of Safety Performance Functions for SafetyAnalyst Applications in Florida

Development of Safety Performance Functions for SafetyAnalyst Applications in Florida

Application of generalized estimating equations for crash frequency modeling with temporal correlation

Speed-consistency Based Safety Evaluation for Freeway Diverging Segments

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