PURPOSES : There are significant differences in traffic accident rates depending on various road conditions and environments. However, the current traffic accident rates on national highways are classified relatively simply, and it is also difficult to accurately calculate the crash modification factor. Therefore, this study aimed to improve the traffic accident rates on national highways by presenting an algorithm for categorizing the traffic accident rates of national highway into four types (older and modern roads, and urban and rural roads). METHODS : The problems in the current rate of traffic accidents were derived, Traffic accident analysis system(TAAS) was used for the traffic accident data, and the road traffic volume statistical yearbook was used for the traffic volume data. After dividing the national highways into older and modern roads and urban and rural roads, the rates of traffic accidents were calculated and compared with the current accident rates. RESULTS : The accident rate of modern roads was found to be lower than that of older roads, and was lower in rural areas than in urban areas. From comparing the results of this study with Korea development institute(KDI) guidelines, older roads and urban roads exceeded the value in the KDI guideline, whereas the rates of modern roads and rural roads were lower than the KDI value. CONCLUSIONS : The accident rate accuracy was improved by subdividing the accident rates into four types. Therefore, it is expected that the accuracy and reliability of economic analysis on road projects will be improved.

PURPOSES: The purpose of this study is to develop a methodology to prioritize sidewalk construction on rural national highways. METHODS : In order to determine an appropriate prioritization for sidewalk construction, we developed a specific methodology. The proposed methodology includes three main steps: 1) Analytic Hierarchy Process (AHP) methods, 2) Subjective evaluation of relevant road agencies for the candidate sidewalks along rural national highways, and 3) Field study conduction. Each step has four phases. The primary feature of this methodology is the addition of expert consultation and survey data, as well as a field study. In addition, the method could guarantee flexibility in selection for evaluation criteria. As a result, the proposed methodology could be used as a general procedure for application to other roadway classifications when considering sidewalk construction. RESULTS: In order to demonstrate the reasonableness of the proposed methodology, a case study was performed for exactly 100 candidate sites for sidewalk construction on rural national highways. All required evaluation scores were properly produced for each candidate site. By doing so, decision-makers can determine the priority for sidewalk construction at these sites by reviewing quantitatively and qualitatively considered data. CONCLUSIONS: The results of the case study can be applied to a long-term fundamental plan for sidewalk construction on rural national highways. Furthermore, this methodology could be employed to prioritize a small-scale SOC project(e. g. bicycle or pedestrian roads).

PURPOSES: Performance evaluation of four types of asphalt concrete overlays for deteriorated national highways. METHODS : Pavement distress surveys for crack rate and rut depth have been conducted annually using an automated pavement survey vehicle since 2007. Linear and non-linear performance prediction models of the asphalt concrete overlays were developed for 43 sections. The service life of the asphalt overlays was defined as the number of years after which a crack rate of 30% or rut depth of 15mm is observed. RESULTS: The service life of the asphalt overlays was estimated as 17.4 years on an average. In 90.7% of the sections, the service life of the overlays was 15 years or more which is 1.5 times the life of conventional asphalt concrete overlays used in national highways. The performance of the overlays was dependent on the type of asphalt mixture, traffic volume levels, and environmental conditions. CONCLUSIONS : The usage of stone mastic asphalt (SMA) and polymer-modified asphalt (PMA) for the overlays provided good resistance to cracking and rutting development. It is recommended that appropriate asphalt concrete overlays must be applied depending on the type of existing pavement distress.

PURPOSES : This study presents the noise level and frequency characteristics investigated in the national highways with the consideration of various measuring conditions and/or methods. METHODS : The noise levels on the asphalt concrete pavement(ACP) and the jointed plain concrete pavement(JPCP) of the national highway were measured and analysed with respect to three variables, i.e., pavement type, surface condition, and measurement distance. The PASS-By method is utilized for the noise measurement and then using CPB spectrum analysis method with 1/3 octave bandwidth, the noise levels and frequency characteristics were calculated for two-second periods before and after the peak noise. RESULTS : Depending on the pavement type, the noise level was changed as the average noise levels are 73.3dB(A) and 78.3dB(A) for ACP and JPCP, respectively. With respect to the effect of surface condition, the average noise levels for crack H(high), M(medium), and L (low) sections are 77.4dB(A), 77.4dB(A), and 78.1dB(A), respectively. Regarding the measurement distance, 1.2meter difference in measuring location reduces 1.6dB(A) of noise level; the average noise levels at 5.3m and 7.5m from the centerline of outer lane are 72.8dB(A) and 71.2dB(A), respectively. It should be noted that the noise levels are slightly different as a function of vehicle speed and type. However, the overall trends for each case was similar. It was found that the domain frequency bands for ACP and JPCP were 400Hz~2000Hz and 500Hz~2000Hz, respectively. CONCLUSIONS : Based on the analysis with the measured noise date from national highway, it was concluded that the noise level and frequency band vary depending on the various conditions. It was also found that some variables significantly affect the noise level while others do not. With further systematic investigation, the comprehensive noise characteristics on the national highway can be achieved. Using such database, it is possible to develop the fundamental noise reduction technology.

차량의 바퀴궤적의 횡방항 변동을 의미하는 원더링(wandering)은 포장의 설계 및 유지보수를 위하여 중요한 요소임에도 불구하고 계측의 어려움 때문에 심도 있게 다루어지지 못하고 있다. 본 연구에서는 왕복 2차로(3.5m차로 폭)와 4차로(3.25m 및 3.5m 차로 폭)인 일반국도 직선 구간에서 차량 바퀴궤적을 조사하여 횡방향 이동 특성을 분석하였다. 조사 결과에서 좌우 바퀴 위치는 서로 다른 분포형태를 보였으며, 포장 설계에 적용할 경우 좌측바퀴에 의하여 얻어진 분포의 특성치가 포장에 미치는 영향이 더 크기 때문에 좌측바퀴의 특성치를 적용하는 것이 합리적인 것으로 나타났다. 좌측바퀴 위치의 평균값은 좌측차선을 기준으로 할 때, 승용 승합차량인 경우 3.25m차로 폭에서 59.5cm, 3.5m일 경우 80.7cm에 위치하였고, 화물차량일 경우 각각 58.4cm와 73.6cm인 것으로 나타났다. 차량 축수에 따른 구분에서 2축 차량의 경우 차로 폭에 따라서 60.7cm와 79.1cm 이고, 3축이상일 경우 44.5cm 및 69.2cm 인 것으로 나타났다. 결국, 바퀴의 중심위치는 차로 폭에 따라 다르며, 그 차는 차로 폭의 차이에 기인하는 것으로 판단된다.

본 연구는 도로설계 시 차로수 결정에 사용되는 적정 설계시간계수값의 특성분석과 적정 설계시간계수값을 적용하는데 있어 세부기준을 제시하기 위해 국내 일반국도 93개 상시교통량 조사지점에서 8년 동안 수집한 시간교통량 및 AADT 자료를 이용하여 AADT 증가와 시간적 변화에 따른 설계시간계수값의 변화를 회귀식 모형을 통해 분석하였다. 회귀식 모형은 30번째 시간교통량을 독립변수로 AADT를 종속변수로 하는 상수항이 없는 단순회귀식으로 구성하였으며, 회귀식은 차로수 구분(2차로, 4차로)과 AADT 수준(3개 그룹)에 따라 별도로 적용하였다. 분석결과, 제안한 회귀식 모형은 추정오차가 작고 모형의 설명력이 높게 나타났으며, 설계시간계수의 시계열적인 변동특성 분석결과, 설계시간계수는 연도별 변화가 크지 않고 차로수 또는 교통량이 클수록 작아지는 특성이 뚜렷하게 확인되었다. 연구의 한계로는 기존방법에서 채택하고 있는 30번째 혹은 100번째 순위의 설계시간계수는 맞다는 가정하에 분석을 진행한 것으로, 주 5일제 확대에 따른 여가통행 증가, 도로의 지역적 교통특성 등에 따른 설계시간계수 변화를 반영하지 못하고 있어 향후에 국내 실정에 맞는 최적순위의 설계시간계수 제시를 위한 연구가 추가적으로 필요하다.