• Journal of the Ergonomics Society of Korea
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• v.36 no.5
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• pp.459-466
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• 2017

Objective: This study examined two traffic signals with a countdown indicator in terms of driver's reaction time and subjective satisfaction score and their performance was compared with a standard traffic signal in driving simulation. Background: Dilemma zone is created when a traffic light changes at intersections. It often pushes drivers to rush in urgent and premature decision making whether to go or stop and thus induces unnecessary mental load among drivers, which may lead to sudden conflicts with following vehicles at intersections. Method: Forty college students (male: 20, female: 20) participated in this driving simulation study. Three traffic signals were employed: (1) standard traffic signal; (2) countdown-separated signal; and (3) countdown-overlaid signal. The countdown-separated and countdown-overlaid signals were designed to inform drivers of the remaining time of a green light before tuning to an amber light. Reaction times (sec) and satisfaction scores (7-point scale) for the two signals with a countdown indicator were compared with those for the standard traffic signal. Results: Reaction times of the countdown-separated (0.49 sec) and countdown-overlaid (0.43 sec) signals were significantly shorter than that of the standard signal (0.67 sec). Satisfaction scores of the countdown-separated (5.3 point) and countdown-overlaid (5.6 point) signals were greater than that of the standard signal (3.8 point). Lastly, the countdown-overlaid signal showed better performance than the countdown-separated signal, but their differences in reaction time (0.06 sec) and satisfaction score (0.3 point) were small. Conclusion: Traffic signals with a countdown indicator can improve drivers' reaction time and satisfaction score than the standard traffic signal. Application: Traffic signals with a countdown indicator will be useful for reducing the length of dilemma zone at intersections, by allowing drivers to predict the remaining time of a green light.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.17 no.3
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• pp.59-71
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• 2018

This study was initiated to develop an optimal signal control algorithm for coordinated signalized intersections using individual vehicle's information which can be collected in a format of prove vehicle data (PVD) via V2I (Vehicle to Infrastructure) communication environment. For developing this signal optimization algorithm, three modules were developed for phase group length computation, split distribution, and phase sequence assignment. The simulation analysis using the microscopic simulation model, Vissim, was conducted for evaluating the effectiveness of the developed algorithm. The analysis result represented that the performance of the developed algorithm is far superior to that of the fixed coordinated signal control method which is the most common signal control method for coordinated signalized intersections in Korea.

• International Journal of Highway Engineering
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• v.17 no.4
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• pp.89-98
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• 2015

PURPOSES : This study evaluated the feasibility of implementing protected-permissive left-turn (PPLT) signals at three-leg signalized intersections. METHODS: A three-leg signalized intersection with permissive left-turn was first selected. A VISSIM simulation model was constructed using data collected from the test site. The VISSIM network was calibrated by adjusting related parameter values in order to minimize the difference between the simulated and surveyed critical gap. The calibrated network was validated by the number of waiting left-turning vehicles per cycle. Finally, the mobility and safety measures were extracted from simulation runs in which permissive, protected left turns as well as PPLTs were realized based on diverse traffic volume scenarios. RESULTS : The mobility-related measures of effectiveness (MOEs) of the case with PPLT outperformed the other two left-turn treatment scenarios. In particular, the average waiting time per cycle for the left-turn vehicles in the case with PPLT was reduced by 30 s. The safety-related MOEs of the case with PPLT were somewhat higher than those in the case with protected left-turns and much higher than those in the case with permissive left-turns. CONCLUSIONS : Based on the mobility- and safety-related MOEs generated from the VISSIM simulation runs, the use of PPLT seems to be feasible at three-leg signalized intersections where the left-turn is permissive and a pedestrian signal exists at the conflicting approach. However, in order to use the PPLT in earnest, it is necessary to revise the road traffic act, traffic signs, and related manuals.

• Journal of Korean Society of Transportation
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• v.27 no.3
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• pp.91-102
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• 2009

A traffic accident prediction model developed using various design variables(road design variables, geometric variables, and traffic environmental variables) is one of the most important factors to safety design evaluation system for roads. However, statistical accident models have a crucial problem not applicable for all intersections. To make up this problem, this study developed AMFs(Accident Modification Factors) through statistical modeling methods, historical accident databases, judgment from traffic experts, and literature review by considering design variable's characteristics, traffic accident rates, and traffic accident frequency. AMFs developed in this study include exclusive left-turn lane, exclusive right-turn lane, sight distance, and intersection angle. Predictabilities of the developed AMFs and the existing accident prediction models are compared with real accident historical data. The results showed that performances of the developed AMFs are superior to the existing statistical accident prediction models. These findings show that AMFs should be considered as a important process to develop safety design evaluation algorithms. Additionally, AMFs could be used as an index that can judge the impact of corresponding design variables on accidents in rural intersections.

• International Journal of Highway Engineering
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• v.19 no.4
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• pp.61-68
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• 2017

PURPOSES : A complete signal system is not always the best solution for improving traffic operation efficiency at intersections. An alternative solution is to use a Protected Permitted Left Turn (PPLT) operation method. However, the PPLT method needs to be developed after a detailed study of driving tendencies, most notably the gap acceptance behavior, for successful implementation. In this study, the gap acceptance behavior was investigated under various variables and weather conditions, especially under rain, and the results were compared to the case of normal weather. The results of this study will be helpful in introducing the PPLT method, and are important considering the tendency of attempting unprotected left turns that is extremely common in Korean drivers. METHODS : Data was obtained by analyzing traffic footage at four intersections on a day when the precipitation was greater than 5 mm/h. The collected data was classified into seven variables for statistical analysis. Finally, we used logistic regression analysis to develop a probability distribution model. RESULTS : Gap, traffic volume, and the number of conflicting lanes were factors affecting the gap acceptance behavior of unprotected left turns under rainy conditions. CONCLUSIONS : The probability of attempting unprotected left turns is higher for larger gaps. On the other hand, the probability of attempting unprotected left turns decreases with an increase in the traffic volume. Finally, an increase in the number of conflict lanes leads to a decrease in the probability of attempting unprotected left turns.

• International Journal of Highway Engineering
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• v.13 no.1
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• pp.69-77
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• 2011

This study is to suggest a methodology to overcome the uncertainty and lack of reliability of data. The fuzzy reasoning model and the neural network model were developed in order to overcome the potential lack of reliability which may occur during the process of data collection. According to the result of comparison with the Poisson regression model, the suggested models showed better performance in the accuracy of the accident frequency prediction. It means that the more accurate accident frequency prediction model can be developed by the process of the uncertainty of raw data and the adjustment of errors in data by learning. Among the suggested models, the performance of the neural network model was better than that of the fuzzy reasoning model. The suggested models can evaluate the safety of signalized intersections in operation and/or planning, and ultimately contribute the reduction of accidents.

• International Journal of Highway Engineering
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• v.9 no.2 s.32
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• pp.1-11
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• 2007

The rapid growths of economy and automobiles since the 1970's have caused serious traffic jams and environmental disruption in urban areas. To relieve these problems caused by urbanization, there should be considered alternative means of transportation modes. Many developed countries have accepted bicycles as a so called "Green Mode" for environmentally oriented strategies to increase the qualities of urban lives. Korea have also attempted various means to raise bicycle usages. In this research, significant factors affecting bicycle crashes at signalized intersections in urban areas were studied. The model results showed that Poisson regression is the best fit methodology for data modeling and revealed that traffic volume, a number of driveways, configuration of the ground, presence of bicycle path, school, and bus stop, residential area, size of intersection are significant factors affecting the bicycle crashes.

• International Journal of Highway Engineering
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• v.20 no.2
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• pp.75-85
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• 2018

PURPOSES : This study aimed to analyze traffic accidents at circular intersections, and discuss accident reduction strategies based on land use and vehicle type. METHODS : Traffic accident data from 2010 to 2014 were collected from the "traffic accident analysis system" (TAAS) data set of the Road Traffic Authority. To develop the accident rate model, a multiple linear regression model was used. Explanatory variables such as geometry and traffic volume were used to develop the models. RESULTS : The main results of the study are as follows. First, it was found that the null hypotheses that land use and vehicle type do not affect the accident rate should be rejected. Second, 16 accident rate models, which are statistically significant (with high $R^2$ values), were developed. Finally, the area of the central island, number of speed humps, entry lane width, circulatory roadway width, bus stops, and pedestrian crossings were analyzed to determine their effect on accidents according to the type of land use and vehicle. CONCLUSIONS : Through the developed accident rate models, it was revealed that the accident factors at circular intersections changed depending on land use and vehicle type. Thus, selecting the appropriate location of bus stops for trucks, widening entry lanes for cars, and installing splitter islands and optimal lighting for motorcycles were determined to be important for reducing the accident rate. Additionally, the evaluation showed that commercial and mixed land use had a weaker effect on accidents than residential land use.

• Journal of Korean Society of Transportation
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• v.25 no.3
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• pp.19-28
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• 2007

Korea's national highways, which emphasize a high level of mobility, serve primarily intercity travel and are used as a detour for freeways. However. at the present. the highways do not have consistent geometric features or other characteristics: for example. some highways have full access control and others have uncontrolled access. Generally, geometric and traffic conditions affect Pronouncedly travel speeds in the highway sections. This study focused on the effect of signalized intersection relative factors on the speeds: signalized intersection densities, signal phases, and volume levels. The study shows that signalized intersection density was the strongest variable affecting the travel speeds: the speeds held fairly constant over intersection densities below 0.3 intersections/km, decreased sharply through intersection density of 0.7 intersections/km. and appeared constant at the lowest level over intersection densities above 0.7 intersections/km. The results also indicate that the effect of signal and traffic volume levels on the speeds was similar to that of the signalized intersection density.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.2 no.1 s.2
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• pp.53-62
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• 2003

This paper demonstrates the in-vehicle dilemma zone warning system (DZWS) project developed as a part of the Driver Advisory and Collision Warning System in Automated Vehicle and Highway System (AVHS). The DZWS project, one of the Korea national ITS projects in 2000 develops the in-vehicle warning device to support drivers' decision making on whether to stop or to proceed to clear the intersection prior to the onset of yellow signal for avoiding the high risk of collision at signalized intersections through the dedicated short range communication (DSRC). This paper explores the design of optimal communication systems between roadway and vehicles, the operational and functional concepts of dilemma zone warning system based on appropriate approach speeds, and the system integration for field test at two sites of signalized intersections. Findings from the system integration indicated that the system would be implemented in eliminating the dilemma zone relative to approach speeds and in reducing red light violations and intersection collisions through the in-vehicle warning device at signalized intersection.