Suk-Ki Lee

An Analysis of Roundabout Application Effects Based on Before and After Field Studies

PURPOSES: Though the situation that the roundabouts are actively constructed, researches on the effect of the roundabouts focus mainly on the analysis of the expected effects of using only traffic simulation on the operation. Considering such problems, this study is conducted to analyze the effects of the various aspects based on field observation studies. METHODS: This study evaluated and analyzed the effects from the aspects of traffic operation, traffic safety, and traffic behavior by performing field observation studies with six roundabouts with/without signal controls on the pilot project areas for the roundabouts installed in 2010. RESULTS: Through the study results, it was found that the average travel time decreases by 14.7% and 2.4% on the signalized intersections and unsignalized intersections, respectively. The average travel speed increases by 9.7 and 5.8km/h on the roundabouts with/without signal lights. Regarding traffic safety, the speed deviation among individual vehicles decreases by approximately 18.4 to 32.7km/h, thus confirming the safety effects. As the decrease of the number of conflicts, it might be explained that car crashes and collision with pedestrians decreased by 62.2% and 66.7%. Also the result shows that the lowest point of speed in roundabouts appears near the yield line on the entry area on the roundabouts. When passing through the roundabouts, vehicles enter at a speed of 20-30km/h, which is the design speed of the circulatory lane and drive out the roundabout with a higher speed than the entry speed. CONCLUSIONS: When a roundabout is introduced at the intersections below certain traffic volume there are effects of traffic operation, traffic safety, and traffic behavior.

Implementing FDWS(Fog Detect & Warning System) with LED Module Structure : Estimation of Safety Effects

Although drivers use various sensory channels to control and navigate their vehicles, they acquire most of all driving-related information visually. In fog, no matter what visual acuity is, the visual channel is useless due to the induced poor visibility. Driv- ers react differently to the adverse weather, resulting in high speed variation. That is why it has the high fatal rate during foggy conditions. Then, it is imperative to provide drivers positive guidance in fog. In this study, the Fog Detect and Warning System (FDWS), being called as the fog lighthouse, was conceived to inform drivers of safety speeds and distances between each vehicle. FDWS includes visibility meters, light bars, and vehicle detectors. The visibility meters calculate sight distances when fog occurs and the estimated sight distances inform drivers through the light bars which are installed at every 30m intervals. The light bars which display red warning lights inform a following vehicle of the position of the leading vehicle to keep the safety distance between the two vehicles. Since the main lights with the high-bright LED (Light Emitting Diode) have high visibilities, drivers can easily recognize far away. Also microwave sensors together with the light bars are installed to detect the presence of vehicles at every 30m intervals. The aim of this paper was to evaluate the effectiveness of the fog system on driver behavior and con- sciousness. As a pilot study, FDWS was implemented on a 1km section of National Highway No. 37 with a divided four-lane, rural highway. The analysis of the driver behavior was based on mean speed with standard deviation, and a questionnaire survey was conducted to estimate the driver consciousness. The results indicates that FDWS significantly led to an about 3kph (for day- time) and 10kph (for nighttime) reduction in mean speed compared to the system turned off. Also the consciousness survey shows

Effectiveness of Road Lighting on Driver` Vision

PURPOSES : Road lighting facilities increase the visibility of road at night in order to improve traffic driver safety and comfort. Generally speaking, current pole lighting has a tendency to create problems of glare and flicker. The phenomenon of glare gives discomfort due to increase of scattered light, when high luminance is in driver`s field of view. The phenomenon of flicker occurs due to the driver passing through discontinuous pockets of pole lighting areas. These phenomenon increase eye strain and decrease driver safety. METHODS : Low height line lighting that distributes light lower than driver`s eye level has been developed and evaluated to reduce the problems linked to current pole lighting. A test was undertaken with 4 conditions(turn on the general pole lighting, turn off alternate pole lighting, turn on the line lighting and line lighting with 50% dimming). A driver written survey was conducted in order to gain driver feedback. RESULTS : Pupil size and brow frequency compared with degree in pole lighting are reduced. CONCLUSIONS : Low height line lighting environment makes drivers more comfortable than pole lighting environment and is positive lighting method in the energy saving and landscape aspect.

Evaluation of Drivers` Detection Distance according to the Local Lightings Condition of Crosswalk Illumination

This study analyzes evaluation of drivers’ detection distance according to the local lightings condition of crosswalk illumination whichcan be installed with or without the continuous lightings; here, continuous lightings mean the lightings installed with a regular spac-ing along the roadside of two lanes and four lanes. The study facilities dummy-detection-distance as a measure of effects observedaccording to the varying lighting conditions; day-time, night-time with continuous lightings only, night-time with the combination ofcontinuous lightings and crosswalk lightings, night-time without lightings at all, and night-time with crosswalk lightings only. Adummy was installed to mimic the school-age-child who are 110 cm tall about to cross the road at crosswalk. Field test was carriedout at two places; one is four lanes operated roads with the continuous lightings and the other is two lanes operated roads without thecontinuous. The corresponding limited speeds are 70 and 60 kph, respectively. With the data of 15th percentile dummy-detection-dis-tance for four lanes operated roads, we conclude the distance for continuous lightings only was not satisfying the Stopping Sight Dis-tance required at 70 kph design speed. The distance was increased with the order of combination of continuous lightings andcrosswalk lightings, day-time condition, and continuous lightings only. With the same data analysis for two lanes operated roads, weconclude the distance for day-time condition only satisfy the Stopping Sight Distance required at 60 kph design speed. Especially, theaverage, 85% tile, 50% tile, 15% tile of a no-night-time lighting (street lamps off) were determined that the subject detection distancewas very shorter than Stopping Sight Distance. Therefore, this insufficient sight distance could make heighten the possibility of accident.Key words : Road Safety, Street Lightings, Crosswalk, Visibility Distance, Stopping Sight Distance

Developing and Evaluation of Coordinated Semi - Actuated Signal Control for Field Application

본 연구에서는 지방부 간선 또는 지선 축에서 효과적으로 사용 가능한 연동형 반감응 신호제어 알고리즘을 개발하고 이를 평가하였다. 연동형 반감응 신호제어에 대한 모의실험 결과를 살펴보면, 주?부 도로의 교통량 차이가 커질수록 연동형 반감응 신호제어의 지체가 최적화된 고정식 신호제어에 비해 감소하는 것을 확인하였다. 그러나 주부도로의 교통량이 같거나 전체 교통량이 많아지면 최적화된 고정식 신호제어의 지체가 더 낮게 나타났으며, 횡단 보행량이 많아질수록 차량 지체가 증가하는 것으로 확인되었다. 따라서 연동형 반감응 신호제어는 차량 교통량이 일정수준 이하인 곳에 적용하되, 횡단 보행량을 고려하여 적용지역을 선별해야 할 것이다.

Evaluating the Effectiveness of Unconventional Intersections on Operation and Environment

PURPOSES : Traffic congestions which occur in the intersections of arterials lead to mobility and environment problem, and then traffic agencies and engineers have been struggling for mitigating congestions with greenhouse gas emissions. As an alternative of solving theses problems, this study is to introduce a low-cost and high-effectiveness countermeasure as unconventional intersections which are successfully in operation in U.S.. The main feature of unconventional intersections is to reroute turning movement on an approach to other approach, which consequently more green time is available for the progression of through traffic. Due to improved progression, this unique geometric design contributes to reduce delays with greenhouse gas emission and provides a viable alternative to interchanges. This study is to evaluate the potential operation and environment benefits of unconventional intersections. METHODS : This study used the VISSIM model with Synchro and EnViVer. Synchro is to optimize signal phases and EnViVer model to estimate the amount of greenhouse gas emissions by each condition. RESULTS : The result shows that unconventional intersections lead to increase the capacity and to reduce greenhouse gas emissions, compared to existing intersections. CONCLUSIONS : Unconventional intersections have the ability to positively impact operations and environments as a low-cost and higheffectiveness countermeasure