Do-Gyeong Kim

Modelling crash frequencies at signalized intersections with a truncated count data model

Modelling crash frequencies provides comprehensive insights into the safety effects of explanatory variables contributing to crash occurrence, and thus a variety of modelling techniques have been employed depending on what variable is of interest. Since accident frequencies are count data which are discrete and non-negative integers, Poisson and negative binomial regression models are used to fit count data with the entire distribution of counts. However, some of the crash counts might be omitted from a sample due to the limits of observability, hence resulting in the truncation of the sample. Without accounting for truncation, the parameters estimated will be biased and inconsistent, and thus careful attention should be paid to the estimation of count data models when a truncation problem exists. This paper describes the development of a truncated Poisson model with zero-truncated count data and the demonstration of differences in estimation results by comparing the results from truncated and untruncated Poisson models with truncated data. The major difference in estimation results is that significant factors included in the both models are not exactly the same. However, it is found that there is no difference in the directions of associations with safety of the significant variables included in the both models.

Use of Digital Tachograph Data to Provide Traffic Safety Education and Evaluate Effects on Bus Driver Behavior

Traffic safety education was conducted with data from a vehicle-mounted digital tachograph device to promote bus driver awareness of safe driving behavior. The objectives were to evaluate the duration of the effects of traffic safety education on abnormal driving behaviors and to identify the differences in education effects between two driver groups: normal and dangerous. A 9-week tracing survey was conducted for 61 bus drivers. Traffic safety education was administered to individual drivers according to their daily driving behaviors. For analysis, a survival model was used to identify the effects of traffic safety education on abnormal driving behaviors. The two main results follow: (a) the effects of safety education decreased more quickly on acceleration-related abnormal driving behaviors than on steering- and deceleration-related abnormal driving behaviors and implied that more concentrated education is required for acceleration-related behaviors and (b) the education effects for the dangerous group lasted longer than for the normal group and implied that abnormal driving behaviors could be reduced if safety education were tailored to the dangerous group. Specialized traffic safety education that reflects individual driving behaviors is recommended for bus drivers, along with periodic traffic safety education to prevent a recurrence (yo-yo effect) in the increased frequency of abnormal driving behaviors.

The Characteristics of Secondary Crashes Occurred on Expressways in Korea

PURPOSES : This study aims to draw differences between primary and secondary crashes by comparing crash characteristics and to identify the unique characteristics of secondary crashes for making better effective countermeasures to reduce secondary crashes. METHODS : The characteristics of secondary crashes were compared to those of primary crashes through a two sample proportional test (z-test). RESULTS : The results showed that vehicle-to-vehicle crashes and vehicle-to-person crashes are dominant crash types in secondary crashes. Compared to primary crashes, secondary crashes were likely to occur during nighttime. With respect to season and weather, the proportion of secondary crashes occurred during winter and in snowy weather is relatively higher than that of primary crashes. The main causes of primary crashes were found to be drowsiness, speeding, and exaggerated steering control, whereas main factors affecting the occurrence of secondary crashes were negligence of keeping eyes forward and no keeping a safe distance as expected. CONCLUSIONS : The characteristics affecting the occurrence of secondary crashes are different from those of primary crashes, indicating that proper countermeasures should be established to prevent the occurrence of secondary crashes on highways.

Investigating the Characteristics of Carsharing Usage Patterns for Public Rental Housing Complexes

The primary objective of this study was to investigate which attributes of HappyCar, a closed carsharing service implemented in rental housing complexes in South Korea, should be improved to become an alternative transportation mode for low-income households. The study also aimed to identify what kinds of characteristics of rental housing complexes influenced the vehicle usage rate. For the analysis, two types of data were collected: survey data from carsharing members and operation record log files provided by a service operator. For the methodology, the study employed an importance-performance analysis (IPA) technique to analyze which attributes of HappyCar require improvement. A beta regression model was estimated to identify factors affecting the vehicle usage rate. The IPA results showed that three attributes—the appropriateness of rental rates, thorough vehicle maintenance, and increase in the number of vehicles operated—should be improved with top priority to make the HappyCar service more convenient and comfortable. Five variables were found to be associated positively with the vehicle usage rate: rental housing type, number of households per complex, ratios of one- and two-person households, and ratio of five or more person households. The study enabled a better understanding of the characteristics of carsharing, including use by low-income residents in rental housing, and provided recommendations for HappyCar service providers and traffic policy decision makers.

Identifying the influences of demographic characteristics and personality of inveterate drunk drivers on the likelihood of driving under the influence of alcohol (DUIA) recurrence

ABSTRACT Driving under the influence of alcohol (DUIA) is one of the main factors that cause severe traffic crashes and is considered a grave offence under the law. As shown by existing research and statistics, one of the characteristics associated with DUIA is that DUIA offenders are more likely to be rearrested for DUIA conviction. This means that in order to eradicate DUIA, the personal, psychological, and socio-cultural characteristics of habitual drunk drivers should be examined and intensive efforts are required to manage these types of offenders. This study aims to identify how the personality traits of DUIA recidivists influence the likelihood of DUIA recurrence on urban roads. The personalities of the drivers were divided into four dimensions – psychoticism, extroversion, neuroticism, and lie – based on the Korean version of the Eysenck personality test. Four additional attributes related to drivers’ information were included: gender, blood alcohol concentration (BAC), drinking frequency, and educational background. From the analysis results, six variables were found to be significant and five variables except for educational background had a positive correlation with the possibility of DUIA recurrence. Regarding drivers’ personality traits, drivers with a higher psychoticism (P) and lie (L) had a 118% and 102% higher possibility of DUIA recurrence, respectively. The results of this study are expected to contribute to a reduction in DUIA-related traffic accidents by preventing DUIA recidivism through follow-up management such as a continuous monitoring for drivers with a higher propensity for DUIA recurrence and by establishing regulations that can administer strong punishments for DUIA recidivists.

Identifying the Factors Affecting the First Traffic Violation Duration by Novice Drivers

PURPOSES : This study deals with first traffic violations occurred by novice drivers, which may be associated with traffic accidents. The objective of this study is to identify what kinds of drivers` characteristics influence on duration till the first traffic violation. METHODS : For the study, Survival Analysis and Cox proportional hazard model, that are usually used in the medical field, were employed. Survival Analysis was conducted to investigate whether there exist differences in survival duration by each covariate, whereas Cox proportional hazard model was used to identify significant factors that affect survival duration till novice drivers violate traffic regulations for the first time after getting a driver license. RESULTS : The results of Survival Analysis indicate that female, age (less than 21), low-frequency examinee of written exam, and non-crash involved drivers have longer duration till the first violation compared to male, greater than 21 years old, high-frequency examinee of written exam, and crash involved drivers, respectively. For the Cox proportional hazard model, license class 1 acquisitor was found to increase the survival duration till the first traffic violation was made, while male, age of 21-24, age of 25-34, age of 45-54, and crash involved drivers were more likely to reduce the survival duration. CONCLUSIONS : Absolutely, traffic violation is closely related to traffic accidents and all of the drivers should keep the traffic regulations to enhance highway safety. The results of this study might provide some insights to construct safe road environments by controlling the factors that reduce the traffic violation duration of novice drivers.

The Effectiveness of Traffic Safety Education to Seniors

While the number of crashes and fatalities has decreased for the last few decades, the proportion of elderly-involved crashes has continuously increased from 19.5% in 2001 to 29.6% in 2008. This paper aims to evaluate the effectiveness of traffic safety education to seniors, which has been conducted for the purpose of providing more systematic knowledge such as safety regulations and making the elderly more aware of the risks of crashes, and eventually to reduce elderly-involved crashes. First, we investigated the levels of traffic safety knowledge of the elder people who attend senior community centers and social welfare centers in Seoul and provided traffic safety education. Then, the effectiveness of traffic safety education was evaluated by using the before-and-after analysis. We set up two different groups to improve the reliability of evaluation: one for control group and the other for comparison group. The results showed that the average scores of the control group after education were significantly improved at the 95% significance level compared to the average scores before education, whereas the comparison group did not show a significant differences in the average scores before and after education except for two questions. This indicates that the levels of traffic safety knowledge of the control group have been improved through education and therefore, the safety education seem to be effective to some extent.