PURPOSES : The purpose of this study is to perform traffic flow characteristics analysis for each point of the long-term work zones and to propose an estimated capacity method to support the establishment of traffic flow management strategies for the long-term work zones. METHODS : The study explained the difference in traffic flow characteristics between the short-term and the long-term work zones, and estimated the capacity of the long-term work zones. The analysis data were collected from five points of long-term work zones of the twolane highway. And VDS and DSRC data were applied to validate data. RESULTS : The characteristics of traffic flow at each measurement point in the long-term work zones showed some differences, among which the capacity was estimated as the starting point to be 1,200 pcphpl and the ending point, 1,400 pcphpl. The delay length was estimated by applying the queuing theory based on the capacity of the start point where the bottleneck starts. As a result of verifying the congestion length based on space diagram map analysis, it was determined that the capacity calculation value and estimation methodology presented in this study were appropriate. CONCLUSIONS : The long-term work zones are mixed with different characteristics of roads, so as the capacity values depending on the analysis location. Therefore, it is necessary to select analysis points and methodologies for estimating capacity and delay depending on the purpose of the analysis, such as estimating the maximum queue length or analyzing the maximum travel time. Through this study, it is expected that by providing accurate information on congestion in advance, road users can detour to other roads, and construction officials can adjust the construction plan to minimize congestion in the construction section.

PURPOSES : This study analyzed explanatory variables, such as dangerous driving behaviors, in a negative binomial regression model, using the Digital Tachograph data of commercial vehicles, to assess the factors associated with freeway accidents. METHODS : Fixed parameter and random parameter negative binomial regression models were constructed using freeway accident data of commercial vehicles from January 2007 to July 2018 on the Gyeongbu Expressway from West Ulsan Interchange to Gimcheon Junction. RESULTS : Six explanatory variables (logarithm of average annual daily traffic, sunny, rainy, and snowy weather conditions, road curvature, and driving behaviors that included sudden stops) were found to impact the occurrence of freeway accidents significantly. Two of these variables (snowy weather conditions and sudden stops among dangerous driving behaviors) were analyzed as random parameters. These variables were shown as probabilistic variables that do not have a fixed impact on traffic accidents CONCLUSIONS : The variables analyzed as random parameters should be carefully considered when the freeway operating authorities plan an improvement project for highway safety.

PURPOSES: The objective of this study is to analyze the effect of superelevation on the existing local freeway ramps where occurrence of traffic incidents are concentrated in order to improve the safety of ramp curves. Using a superelevation slope test conducted on Cheong-ju interchange as a case study, operating speed and lateral friction coefficients are measured, and the safety before and after increasing the superelevation is analyzed. METHODS: First, the actual operating speed of freeway ramps is measured for analysis and the 85th-percentile speed is calculated. This is followed by a measurement change in the lateral friction coefficient because of an increase in superelevation slope from 6% to 10%. Based on the change in lateral friction coefficient, an evaluation of the safety of driving mechanics is carried out and suggestions for the most appropriate superelevation slopes are presented. RESULTS: The operating speed (V85) of the loop ramp increases by up to 5.6 km/h after increasing the superelevation slope, and the operating speed (V85) of reverse ramp curve increases by up to 6.1 km/h. However, the standard deviation of the speed between each section has decreased, making it easier to drive smoothly. Although some sections of the loop ramp show poor safety due to the difference between actual and design friction coefficients in the safety evaluation before the increase of superelevation slope, the lateral force decreases after the increase of superelevation slope, improving the safety of the road. CONCLUSIONS : Currently, Korea’s freeway ramps pose a safety risk to vehicles traveling at speeds higher than the design speed. To improve the safety of freeway ramps, analysis on the effect of increase in superelevation slope found that the lateral friction coefficient decreases, which in turn improves the safety of freeway ramps.

PURPOSES : This study aimed to evaluate the influence of weigh-in-motion (WIM)-based overloading enforcement systems on the performance of a traffic stream. METHODS: A VISSIM simulator was used for the evaluation of various scenarios. Actual WIM event data collected from the field was used for simulation parameter calibrations. A genetic algorithm was incorporated into the calibration procedure to identify the optimal set of parameters. The impact of the overloading enforcement systems on the traffic stream was investigated from the perspective of mobility, safety, and environmental compatibility. RESULTS: The existing enforcement system is generally superior to the new pilot enforcement system. CONCLUSIONS : Policies and regulations to fully exploit the benefits of WIM-based enforcement systems on freeways need to be developed and implemented. In addition, various enforcement scenarios should be tested on both actual and simulated environments.

PURPOSES: In this study, design elements of rest areas for drowsy drivers are classified and appropriate criteria for each design element are presented. METHODS : By comparing and analyzing the design criteria for rest areas, the most appropriate installation criteria were suggested by considering the driving patterns of rest area users. RESULTS: As a result of the study, elements influencing the design of rest areas for drowsy drivers are suggested such as installation location and installation type. In addition, proper separation distance between resting areas was suggested considering vehicle flow, users’fatigue and physiological needs. Other criteria for rest areas were also suggested. CONCLUSIONS : Proper safety facilities were not installed in rest areas because appropriate criteria were not established. In this study, design elements were derived and installation criteria were designed so that rest areas could be used safely and conveniently.

PURPOSES: The objective of this study is to estimate required minimum spacing between Freeway IC for high-speed roadways. METHODS: Since high-speed roadways with over 140 km/h design speed do not exist in Korea, VISSIM Simulation Program was used for analysis. Acceleration noise and conflicts were selected for Evaluation Index. Standard deviation size for acceleration and deceleration was calculated by VISSIM to estimate acceleration noise. Conflicts were produced in areas between Freeway IC with SSAM. RESULTS : As a result, required minimum spacing was 6 km for acceleration noise analysis, while 5 km was deducted for conflict analysis. For Model Evaluation, with SAS, conflicts did not show much difference in 5~6 km area by 90% confidence interval. CONCLUSIONS : For acceleration noise, results showed lacking in its discrimination between index per Minimum Spacing. However, conflicts were valid in difference; required minimum spacing was 5 km by validation result.

OBJECTIVES : Many roadway departure crashes on the freeway interchange are due to the running speed being greater than the design speed. This study aims to ensure a safe and pleasant driving experience for the driver by increasing the superelevation based on the running speed on the highway interchange ramp. METHODS: The mean running speed for each type of ramp is calculated on site survey more than 10 interchanges. Using the mean running speed, we calculated the superelevation and the side friction using the method given in “A Policy on Geometric Design of Highways and Street”(Pages 145-166, 2001). Then, we applied the modified method to the superelevation range. Finally, we ensured safety using the Degree of Safety that is proven by the centrifugal acceleration ratio as suggested by Joseph Craus (1978). RESULTS : The mean running speeds are 50 km/h and 65 km/h when the design speeds are 40 km/h and 50 km/h, respectively. After the application of the new method used in this study, the superelevation will be increased by 9.0% and 10.0% when the mean running speeds are 50 km/h and 65 km/h, respectively. CONCLUSIONS: A higher superelevation can give the driver a more comfortable and safe driving environment. However, the driver needs to be aware of snow and low-temperature conditions.

PURPOSES: This study analyzed the lane-by-lane traffic flow characteristics in Korea by using real-world data, including congestion levels, for 2-, 3-, and 4-lane freeways. METHODS : On the basis of a literature review, lane flow and speed characteristics were analyzed using flow measurements and speed ratios. In addition, the effect of congestion levels on traffic flow were visualized using rescaled cumulative plots. RESULTS: Driver behavior varied depending on the congestion level. During free-flow conditions, the lane-use ratio of individual lanes varied largely, whereas during congestion, the ratio was nearly the same for all lanes (i.e., equilibrium). During maximum-flow and congestion conditions, the median lane was used more than the shoulder lane, whereas during all other conditions, the shoulder lane had a higher lane-use ratio. In 3- or 4-lane freeways, the lane-use ratio of the median lane always exceeded 1 and was the highest during free-flow conditions. CONCLUSIONS : The results of the present analysis can be used as an index to predict congestion before a lane is overcapacitated. Moreover, the results can be applied in variable lane guidance systems, such as car navigation systems and variable message displays, to control traffic flow.

PURPOSES: The purpose of this study is to develop a methodology for estimating additional carbon emissions due to freeway incidents. METHODS : As our country grows, our highway policy has mainly neglected the environmental and social sectors. However, with the formation of a national green growth keynote and an increase in the number of people interested in environmental and social issues, problems related to social issues, such as traffic accidents and congestion, and environmental issues, such as the impact of air pollution caused by exhaust gases that are emitted from highway vehicles, are beginning to be discussed. Accordingly, studies have been conducted on a variety of environmental aspects in the field of road transport, and for the quantitative calculation of greenhouse gas emissions, using various methods. However, in order to observe the effects of carbon emissions, microscopic simulations must use many difficult variables such as cost, analysis time, and ease of analysis process. In this study, additional greenhouse gas emissions that occur because of highway traffic accidents were classified by type (incident handling time, number of lanes blocked, freeway level of service), and the annual additional emissions based on incidents were calculated. According to the results, congestion length and emissions tend to increase with an increase in incident clearance time, number of occupied lanes, and worsening level of service. Using this data, we analyzed accident data on the Gyeong-bu Expressway (Yang-Jae IC - Osan IC) for a year. RESULTS : Additional greenhouse gas emissions that occur because of highway traffic accidents were classified by type (incident handling time, number of lanes blocked, freeway level of service) and annual additional emissions caused by accidents were calculated. CONCLUSIONS: In this study, a methodology for estimating carbon emissions due to freeway incidents was developed that incorporates macroscopic flow models. The results of the study are organized in the form of a look-Up table that calculates carbon emissions rather easily.

PURPOSES: The objective of this study is to analyze factors affecting traffic accident severity for determining countermeasures on freeway climbing lanes. METHODS : In this study, an ordered probit model, which is a widely used discrete choice model for categorizing crash severity, was employed. RESULTS: Results suggest that factors affecting traffic accident severity on climbing lanes include speed, drowsy driving, grade of uphill 3%, gender (male offender and male victim), and cloud weather. CONCLUSIONS : Several countermeasures are proposed for improving traffic safety on freeway climbing lanes based on the analysis of crash severity. More extensive analysis with a larger data set and various modeling techniques are required for generalizing the results.

PURPOSES : This study aimed to develop a new highway capacity estimation method and provide comparative results among traditional capacity estimation methods and the recommended values in the latest version of KHCM. METHODS : The limitations of the existing methods, such as inconsistency and underestimation of the capacity value, are summarized through an extensive literature review. To overcome these limitations, a new method is introduced by adopting a definition of capacity and traffic flow characteristics at or near breakdown points. This method can produce the capacity value by searching a point corresponding to the maximum traffic flow through analysis of gradient changes (point of inflection) of the traffic flow and speed distribution. Comparative results of capacity values from each method are also presented to validate the new method by using data collected from detectors on freeways. RESULTS: From the analysis results, it is shown that a consistent capacity value can be estimated by applying the new method. In addition, the resulting capacity values are 3%-4% higher than those recommended in KHCM. CONCLUSIONS : The capacity values listed in the current KHCM tend to produce underestimated results. The new method presented in this paper may be included in the future edition of KHCM.

PURPOSES: This study analyzes the characteristics of traffic flow on freeway sections under daytime and nighttime conditions to improve traffic safety, and suggests a method to estimate an accurate freeway capacity value that reflects these characteristics. METHODS : The trends and differences in capacity were investigated using comprehensive field data collected under both daytime and nighttime conditions on freeway sections with designated speeds of 80, 100, and 120 kph. RESULTS : The capacity values under nighttime driving conditions were reduced by 3.3%, 6.9%, and 8.8% at 80, 100, and 120 kph, respectively. Several nighttime adjustment factors were deduced for each designated speed category from the analysis results. CONCLUSIONS : It is expected that more accurate capacity values can be estimated for freeway sections under nighttime conditions by applying the resulting adjustment factors. In addition, traffic safety will be improved through the increased efficiency of traffic management on these freeway sections.

PURPOSES : It is well known that experts determined the current standard dimensions of freeway lane markings. However, rigorous engineering rationale could be insufficient regarding whether or not the standard dimensions account for how visible the markings are to the driver. In this study, we seek to optimize the dimensions of freeway lane markings to improve their visibility to drivers. METHODS: The study was conducted as follows. First, alternative lane marking dimensions were selected which could be installed in a test construction site. Second, a video recording was made while driving on the test construction site. Third, subjects were shown the recorded video and then instructed to indicate their preference from among the various lane markings. Lastly, t-tests were applied to assess the statistical significance of differences in the preferences expressed. RESULTS : According to the t-test results, there was no significant difference in the preferences expressed regarding the lane marking widths. However, with regard to the dimensions of freeway lane marking, which represents line marking lengths, gap lengths, and widths of marking, the subjects expressed a preference for specific dimensions such as 6 m:12 m,13 cm, 8 m:12 m,10 cm and 6 m:12 m,10 cm. CONCLUSIONS : In considering the dimensions of freeway lane markings and their relation to visibility by the driver, it was found that dimensions such as 6 m:12 m,13 cm, 8 m:12 m,10 cm and 6 m:12 m,10 cm.

PURPOSES : The purpose of this study is to identify the factors affecting the effectiveness of speed limit change that is defined as the amount of increased travel speed. METHODS: A ordered logit model was adopted to analyze the relationship between the change in travel speed and contributing factors. A stretch of Kyungbu freeway was selected for the analysis because the Korea expressway corporation has raised speed limit from 100km/h to 110km/h since September 1st in 2010. RESULTS: The results showed that geometric design elements, speeding cameras, and section length were identified as factors contributing the effectiveness. Contributing geometric design elements include the number of horizontal curves and vertical curves that do not meet the design requirement with 110km/h speed limit. CONCLUSIONS: The outcome of this study will be used for establishing various traffic operations and control strategies for freeway speed management.

PURPOSES : Adverse weather conditions such as heavy rain, heavy snowfall, and thick fog and so on have highly affect on the change in traffic conditions on the road. In particular, heavy snowfall causes capacity reduction as well as crash occurrence. This study investigated the effects of snowfall on speed on a freeway. METHODS : Vehicle detection systems data were matched with corresponding weather station data by regression analysis. RESULTS : The results show that the travel speed is reduced by 6.7% under little snowfall and by 12.8% under heavy snowfall. Regarding the speed variation, 8.7% and 114.7% increases are observed under little snowfall and heavy snowfall, respectively. It is also found that 1 cm increase in snowfall leads to 0.4% decrease in travel speed. In addition, the travel speed increases by 0.4% when the temperature increases by 1℃. CONCLUSIONS : It is expected that the outcome of this study will be useful in establishing more effective strategies for winter operations and road maintenance in practice.

도로교통 안전진단은 도로의 계획 및 설계단계에서부터 교통사고가 발생할 수 있는 요소를 찾아내 미리 개선하고 건설 후 운영단계에도 도로구조나 안전시설이 사고방지에 적정한지를 평가하는 예방적 차원의 안전성 강화 제도이다. 이 제도는 2000년대 초에 우리나라에 소개된 이래 다양한 사업이 진행되어 왔고 법제화되었으며, 사업의 지속화를 위해 현재까지 진행된 사업에 대한 평가가 필요한 시점이다. 이러한 필요성에 따라 본 연구에서는 공용중인 고속도로의 교통안전진단사업에 대한 효과 평가를 수행하였다. 연구의 공간적 범위는 영동고속도로이며 2005년과 2006년도에 시행된 안전진단사업에 대해 전후 2년을 평가기간으로 하여 분석하였다. 평가방법은 관찰적 사전 사후 평가방법 중 경험적 베이즈 방법을 적용하였다. 효과평가 결과 사업이 시행된 대부분의 구간에서 개선효과가 있는 것으로 나타났으나 일부 구간에서는 효과가 없거나 미미한 것으로 나타났다. 이를 각 구간별 개선조치 내용과 비교하여 검토한 결과 해당 구간에 여러 개선조치가 시행된 경우 효과가 양호하게 나타났으며, 효과가 나타나지 않는 구간은 개선조치가 적거나 단일한 경우가 일반적이었다. 이러한 결과를 바탕으로 개선효과가 나타나지 않는 구간에 대해서는 구체적인 분석과 대응책 마련이 가능할 것이다. 또한 향후 공용중인 고속도로 안전진단사업의 사업내용 및 방향설정 등에 참고로 활용될 수 있다.

교통사고발생시 사고 심각도에 영향을 미치는 요인과 그 관계를 이해하는 것은 기하구조나 환경 측면에서 교통사고 발생을 예방하고 운전자와 사고 차량의 특성을 이해하는데 도움을 준다. 본 연구에서는 계층 이항 로지스틱모형에 의해 고속도로 교통사고 심각도에 영향을 미치는 요인을 파악하고 영향변수 간 차이를 나타내는 비교위험도(odds ratio)를 도출하였다. 사고 심각도는 인명피해와 차량피해로 구분하여 사망사고모형과 차량완파사고모형을 구축하였다, 종속변수는 사망자 발생과 완파차량 발생 여부이며, 각각 사고-탑승자, 사고-차량의 2수준 계층구조를 적용하였다. 추정 결과 설명변수의 고정효과는 두 모형이 유사한 결과를 보이나 종속변수의 속성에 따라 차별화된 결과를 나타내기도 하였다. 본선과 진출입부에서의 사고가 가장 위험하며, 중앙선 침범과 통행위반, 과속 사고의 상해나 차량 파손 위험도가 높고, 충돌사고와 추돌사고, 화재 사고의 피해가 크다. 사고 심각도는 노면 상태나 시야 조건 등 외부환경에 영향을 받으나 기하구조 조건은 관련이 없다.

본 연구의 목적은 차종별 교통류 모형을 이용한 편도 2차로 고속도로 공사구간의 용량 값을 산정하는 것이다. 공사구간의 교통류 모형은 공사구간의 유입부 및 유출부를 대상으로 차종별 모형과 승용차 환산계수를 적용한 전체 차량에 대한 모형으로 도출하였다. 차종별 모형에서 산정된 최대교통류율은 승용차환산계수 및 중차량 비율을 적용하여 공사구간의 용량 값으로 전환하였다. 차종별 모형의 유입부 및 유출부 최대교통류율 값은 각각 1,845pcphpl과 1,884pcphpl로 산정되었으며 차량 전체를 대상으로 한 모형의 최대교통류율은 차종별 결과보다 높게 분석되었다. 모형의 비교 검증을 위하여 최대밀도에 따른 거리 차두간격을 적용하였다. 공사구간의 용량은 공사구간의 흐름이 안정된 유출부 용량보다 공사구간 진입을 위한 차선 변경 등으로 교통흐름이 원활하지 못한 유입부 용량에 좌우되므로 유입부 교통류 모형의 최대교통류율 값인 1,800pcphpl을 편도 2차로 고속도로 공사구간 용량 값으로 산정하였다.