The study investigates data concerning crashes at roundabouts in order to identify the major factors influencing such events in South Korea. In this investigation, three stages of research tasks were carried out. First, crashes which occurred at South Korean roundabouts were categorized and subsequently compared with international cases. Second, field surveys were conducted in order to investigate how vehicle speeds influence the occurrence of accidents. Third, a statistical analysis was performed in order to investigate the correlation between roundabout geometry and crash occurrences and to reveal major geometric elements of roundabout safety. It was revealed in the study that most vehicles slow down substantially around roundabouts and recover their speed after the roundabouts. Based on the statistical analysis, it was found that negative binomial distribution would give a better performance. In addition, in contrast to cases in the US, the final selection of the independent variables includes as follows: the number of approaches, the number of entering lanes, the entry width, the flare width, the number of circulating lanes and the circulating lane width. Finally, the study provided a model with which to capture the relationship between geometric design elements and the occurrence of crashes at roundabouts. It is anticipated that this model will be applied by engineers to better predict crash occurrences at roundabouts.

This paper presents a sidewalk pavement width design method for making more pedestrian friendly and walk-inspiring sidewalk pavements in the urban area. Instead of using the current sidewalk pavement width design standard that usually leads to having minimum values, this research investigated pedestrians’ preferences on the levels of service, surveyed actual foot path trajectories in the sidewalk pavements, and observed pedestrian movement characteristics in the streets. Further, these investigation results were summarized to propose a new urban sidewalk pavement width determination procedure. The proposed procedure was applied in a case study site in Seoul, and its application resulted in a much higher pedestrian level of service. It is anticipated that the proposed method should be of service in both planning and retrofitting urban streets to make more pedestrian sensitive street designs.

Hard shoulder running (HSR) has been increasingly used as a sustainable and viable way to increase road capacity. This study investigated the safety effect of HSR on freeways in South Korea using the empirical Bayes method. This study found an increase in the total number of crashes. In terms of crash severity, a higher proportion of crashes (25.3%) on 2(3)-lane sections were found to be serious (involving injuries and/or fatalities) compared to those on 4(5)-lane sections (3.6%). Also, a positive relationship was found between the length of the hard shoulder running and changes in crash frequencies. Thus, hard shoulder running on lengthy 2(3)-lane freeways should be avoided.

This paper presents the safety effects of highway terrain types in a crash model developed for South Korean rural national roads. This research was necessary because despite terrain type being one of the major factors determining the design speed of highways, their specific safety effects on actual crash occurrences and severity have not been fully investigated. It is the author’s view that when the design speed is changed, the terrain types will have some safety effects. To check this view, a statistical analysis was performed with an ordinal logistic regression model in order to relate several independent variables of highway geometric elements such as terrain type, tangent length, curve length, radius of curvature and vertical grade to actual crash occurrences. Through this investigation, terrain type was found to be a significant independent variable that explains crash occurrences for rural arterial roads in South Korea. Next, an attempt was made to develop crash cost estimation models for each terrain type. This was necessary because practicing engineers should be able to estimate the impacts of using different highway geometric designs on accrued crash costs. The models developed indicate that highway radius of curvature and median designs influence crash costs noticeably in flat areas, whereas vertical grade and shoulder width do so in mountainous areas. These findings seem to capture more detailed crash trends using different highway geometric designs and they should be helpful in designing safer highways.

This paper presents the results of a study which examined accident modification factors for median bus lanes on urban arterials. Although taken for granted that median bus lanes will boost bus ridership and relieve traffic congestion, the full utilization of this useful design is not undertaken because highway engineers often are concerned with the increase of crashes in median bus lanes. However, the installation of the median bus lanes does not always lead to an increase in crashes and, to demonstrate that this argument is correct, this research proposes the use of accident modification factors. The following tasks were carried out: first, aliterature review of the major geometric elements of median bus lanes was undertaken. Second, both existing crash and geometric information data were gathered. Third, a statistical analysis was made to examine the effects of crash occurrences on major geometric elements. In addition, the crash models resulting from this analysis were subsequently applied in developing accident modification factors. A verification process was also carried out. As a result, it was found thataccident modification factors for median bus lanes could be successfully developed, and that crash occurrences were very sensitive to the widths of the bus lane, the travel lanes and the shoulders, in that order. The findings from this research should be useful in comparing several safety design alternatives in the future.