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.

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: Design of approach roads of rest areas in highway has many drawbacks such as geometric design elements. There has been traffic accidents occured in these approach roads of rest areas. Thus, design criteria is required in order to protect accidents from being occurred. In case of Korea, geometric structure design criteria of entry facilities, such as toll-gate, interchange, junction etc was established. However there are no presence in a detailed standards for geometric structure of the rest area which affiliated road facilities. METHODS: In this study, analytic on accidents was carried out in regards to the entry of geometric structure of resting areas by utilizing a sight survey and an investigation research of traffic accidents. The survey was targeting 135 general service areas. Collisions with physical channelization and safety facilities occurred due to speeding, rapid entry, and etc at the entrance nose section. At the entrance connector roads, accidents caused by speeding, negligence, over-operation of handle of drivers were main reason of accidents. Discriminant analysis were conducted about geometric elements to distinguish influencing factors for traffic accidents. the lengths and access angles of the entrance connector roads were regarded as to have the high relation with traffic accidents. RESULTS: After classifying the design section of resting areas' entry as well as derive design elements on each section, a speed measurement by targeting entry of rest areas and car behavior surveys were performed, then each element's minimum standard was derived through the analyses. According to the speeds at the starting/end point of entrance connector road, the range of the junction setting angle of the entrance connector road is defined as 12˚~17˚ and the connector length model was suggested. CONCLUSIONS: Suggest improvement plans for existing rest areas that can be applied realistically. This should be corresponded to the standards of entry and exit of developed rest areas.

PURPOSES: Using the collected data for crash, traffic volume, and design elements on ramps between 2007 and 2009, this research effort was initiated to develop traffic crash prediction models for expressway ramps. METHODS: Three negative binomial regression models and three zero-inflated negative binomial regression models were developed for individual ramp types, including direct, semi-direct and loop, respectively. For validating the developed models, authors compared the estimated crash frequencies with actual crash frequencies of twelve randomly selected interchanges, the ramps of which have not been used for model developing. RESULTS: The results show that the negative binomial regression models for direct, semi-direct and loop ramps showed 60.3%, 63.8% and 48.7% error rates on average whereas the zero-inflated negative binomial regression models showed 82.1%, 120.4% and 57.3%, respectively. CONCLUSIONS: Conclusively, the negative binomial regression models worked better in traffic crash prediction than the zero-inflated negative binomial regression models for estimating the frequency of traffic accidents on expressway ramps.

PURPOSES: Because expressway ramps are very complex segments where diverse roadway design elements dynamically change within relatively short length, drivers on ramps are required to drive their cars carefully for safety. Especially, ramps on expressways are designed to guarantee driving at high speed so that the risk and severity of traffic accidents on expressway ramps may be higher and more deadly than other facilities on expressways. Safe deceleration maneuvers are required on off-ramps, whereas safe acceleration maneuvers are necessary on onramps. This difference in required maneuvers may contribute to dissimilar patterns and severity of traffic accidents by ramp types. Therefore, this study was aimed at developing prediction models of the severity of traffic accidents on expressway on- and off-ramps separately in order to consider dissimilar patterns and severity of traffic accidents according to types of ramps. METHODS: Four-year-long traffic accident data between 2007 and 2010 were utilized to distinguish contributing design elements in conjunction with AADT and ramp length. The prediction models were built using the negative binomial regression model consisting of the severity of traffic accident as a dependent variable and contributing design elements as in independent variables. RESULTS: The developed regression models were evaluated using the traffic accident data of the ramps which was not used in building the models by comparing actual and estimated severity of traffic accidents. Conclusively, the average prediction error rates of on-ramps and offramps were 30.5% and 30.8% respectively. CONCLUSIONS: The prediction models for the severity of traffic accidents on expressway on- and off-ramps will be useful in enhancing the safety on expressway ramps as well as developing design guidelines for expressway ramps.

현행 고속도로 연결로 중 감속차로의 길이는 자유교통류 상태에서 유출차량이 본선과 유출부 사이의 속도의 차이에 적응할 수 있는 제동거리로써 결정된다. 그러나 실제 도로의 운영상태에서는 항상 자유교통류 상태를 유지할 수 없으며 때로는 유출부에서 대기행렬이 형성되게 된다. 대기행렬은 그 이후 접근하는 유출차량이 감속차로 이전에서부터 감속을 해야 하는 상황을 발생시켜 본선 교통류에 영향을 주게 될 뿐만 아니라, 일부 입체교차로에서는 감속차로의 길이보다 더 길게 대기행렬이 형성됨으로 인하여 본선 최하위 차로까지 점유하게 되어 소통 및 안전에 큰 지장을 초래하고 있다. 본 연구에서는 이러한 문제를 해결할 수 있는 대안을 개발할 수 있는 방법론을 개발하기 위하여 충격파 이론을 적용하여 본선 및 유출부의 교통량, 설계속도 등에 따른 유출부 감속차로에서의 대기행렬 길이를 산정하여 현행 감속차로의 길이와 비교하였다. 그리고 대기행렬이 본선 교통류에 대한 영향을 최소화할 수 있도록 감속차로의 수에 따른 대기행렬길이의 변화도 분석하였다. 결과에 의하면 유출램프의 설계속도를 10km/h 상향시킴으로써 대기행렬의 길이는 10% 감소되며, 램프의 차로수를 1개에서 2개로 증가시키게 되면 50%의 대기행렬 감소를 기대할 수 있는 것으로 분석되었다.

본 연구는 도로연장측면에서 본선에 비해 상대적으로 연결로에서 발생하는 사고빈도가 높고, 교통사고가 증가하는 추세인 고속도로 연결로의 교통사고 예측모형의 개발에 초점을 두었다. 연결로 유형별(직결, 준직결, 루프)로 통계적으로 유의한 사고인자를 선정하고, 사고율과의 관계가 비선형 임을 분석하여 변수를 변형(Variables Transformation)하여 All possible 방식으로 예측모형을 개발하고, 통계적 진단 및 검증을 거쳐 유의성을 확인하였으며 이에 기존 개발 모형에 비해 예측력이 더욱 우수한 결과를 보였다. 개발된 사고예측모형은 보다 비용면에서 효율적이고, 안전한 트럼펫형 IC 연결로의 설계와 연결로 교통사고 원인분석에 활용될 수 있을 것으로 기대된다.

본 연구는 개선된 한국형 도로용량편람 작성 작업의 일환으로 고속도로 연결로 접속부에 대한 분석방법에 관해 검토한 것으로 1992년에 작성된 우리나라의 도로용량편람(92KHCM)과 최근에 발표된 미국의 도로용량편람(USHCM2000)의 분석방법론을 비교 검토하여 국내에서의 적용가능성을 타진하고 최적의 분석방법을 정립하고자 하였다 이를 위해 본 연구의 대상구간을 설정하고 기존 방법론을 이용하여 현장 관측치와 비교 평가한 후 수집된 자료들을 분석토록 하였다. 자료의 수집 및 분석 결과 접속차로 1개만을 고려한 92KHCM의 경우 평가에 사용된 모형식에 의한 추정치와 실제 관측치가 다소 차이를 보였으나 접속차로 2개를 고려한 2000USHCM 의 경우 계산치와 관측치가 거의 일치함을 알 수 있었다. 이를 통해 2000USHCM에서의 분석방법론이 보다 합리적인 면이 많이 내포되어 있음을 확인 할 수 있었다. 또한 서비스 수준의 판정기준으로 영향권의 밀도가 사용되어 졌으며 이전의 속도에 비해 교통량의 증가에 따른 민감도가 우수함을 알 수 있었다. 본 연구에서의 분석대상 구간은 독립적인 합류부에 국한하였으나 추후 본 연구는 보다 광범위한 자료의 수집을 통해 연속적인 분류 합류 연결로 접속부에 대한 연구로 확대가 되어야 할 것으로 판단된다

From the traffic analysis, and model constructions and verifications for speed prediction on the freeway ramp junctions with 70mph speed limit, the following results were obtained : ⅰ) The traffic flow distribution showed a big difference depending on the time periods. Especially, more traffic flows were concentrated on the freeway junctions in the morning peak period when compared with the afternoon peak period. ⅱ) The occupancy distribution was also shown to be varied by a big difference depending on the time periods. Especially, the occupancy in the morning peak period showed over 100% increase when compared with the 24hours average occupancy, and the occupancy in the afternoon peak period over 25% increase when compared with the same occupancy. ⅲ) The speed distribution was not shown to have a big difference depending on the time periods. Especially, the speed in the morning peak period showed 10mph decrease when compared with the 24hours'average speed, but the speed did not show a big difference in the afternoon peak period. ⅳ) The analyses of variance showed a high explanatory power between the speed predictive models(SPM) constructed and the variables used, especially the upstream speed. ⅴ) The analysis of correlation for verifying the speed predictive models(SPM) constructed on the ramp junctions were shown to have a high correlation between observed data and predicted data. Especially, the correlation coefficients showed over 0.95 excluding the unstable condition on the diverge section. ⅵ) Speed predictive models constructed were shown to have the better results than the HCM models, even if the speed limits on the freeway were different between the HCM models and speed predictive models constructed.