PURPOSES : This study aims to conduct a sensitivity analysis to determine the major factors affecting traffic accidents involving elderly pedestrians. METHODS : In this study, a regression tree model was built based on a non-parametric statistical model using data on traffic accidents involving elderly pedestrians. Using this model, we analyzed the degree of change in the probability of pedestrian fatalities. RESULTS : Results of the model analysis show that the first major factor combination affecting traffic accidents involving elderly pedestrians is speeding, night time, and road markers. The second combination is night time and arterial roads (national and local highways). The last combination that may lead to such accidents is heavy vehicles and federally funded local highways. CONCLUSIONS : Preventive measures, such as speed control, proper lighting, median strips, designation of pedestrian protection zones, and guidance of detours, are necessary to manage high-risk combinations causing accidents of the elderly.

PURPOSES : This study predicts the concentration of suspended road dust (PM10) by analyzing meteorological, traffic, and atmospheric environmental data acquired at various angles, and attains a comprehensive understanding of the influencing factors of suspended road dust. METHODS : Experimental field methods were applied and statistical analyses were conducted. Field experiments were conducted using a vehicle-based measurement of suspended dust (PM10) to measure its concentration at the measurement site while maintaining a constant driving vehicular speed. Statistical analysis demonstrated the effects of the concentration of suspended dust on changes in meteorological and environmental factors and lanes per traffic volume at the time of measurement. Finally, a multiple linear regression model was applied to identify the factors which affected the generation of suspended dust. RESULTS : The analysis of suspended road dust concentrations according to the lanes per traffic volume and environmental factors showed that suspended dust concentrations increased at increasing driving speeds. In addition, the background concentration at the monitoring station was higher at high-wind speeds (>3.0 m/s) than at low-wind speeds (<1.6 m/s), but the suspended dust concentrations were higher at low-wind speeds. During the temperature inversion period from evening to morning, the suspended effects of traffic and meteorological factors were greater than the background concentration at the station. Multiple linear regression analysis showed that excluding yellow-dust days, which are known to affect atmospheric pollution levels, the accuracy of the model improved and resulted in increases in background PM10, vapor pressure, sea-level pressure, visibility, after-rainfall time, and in decreases in insolation and precipitation during low-wind speed conditions. CONCLUSIONS : At low-wind speeds, 5 days after rain, and when the relative humidity was higher than 72%, suspended dust was found to be higher than atmospheric PM10 concentration and may increase at increasing driving speeds and section lane traffic volumes. However, the volume of measured data in this study is limited to determining the patterns of suspended dust, as the silt loading of the operational road or the effects of prominent variables were not considered in this study. However, we identified prominent factors related to road-suspended dust for real-time road-dust predictions.

PURPOSES : Traffic congestion on freeway generally occurs when the traffic volume exceeds the road capacity. Most traffic manuals *such as the Korean Highway Capacity Manual) present the highway capacity as approximately 2,000 units/hour. However, in the real world, freeway congestion occurs for various reasons, including unusual driver behaviors, physical road limitations, and large traffic volumes. Thus, the flow rate at a traffic breakdown can have a wide range of volumes. Therefore, using 5-min volume and speed data from the field, this study explores the stochastic features of traffic breakdowns on major urban freeways in Seoul. METHODS : First, a breakdown point is defined by applying a wavelet transform to identify the sharp drop in the speed data near freeway bottlenecks. Second, based on the flow rate at and before a breakpoint, a survival analysis is performed to construct the probability distributions of the traffic breakdown. Log-rank tests are also conducted to verify the similarities of the distributions between freeways. RESULTS : The analysis results confirm the stochastic features of the urban freeways in Seoul. Specifically, the freeways have typical S-shaped distributions of breakdown probabilities. However, the distributions rise steeply (exceeding a 50% of breakdown probability) at flow rates of 1,150 vphpl to 1,700 vphpl; this is lower than the general expectation. CONCLUSIONS : The statistical differences in the probability distributions for freeways indicates that applying a general standard to every urban highway could raise problems. This study has a limitation in identifying the specific causes of traffic congestion owing to the by physical relationships between individual vehicles. An investigation if vehicle trajectory data should be conducted to examine these aspects in further detail.

PURPOSES : This study investigated the field applicability of pervious concrete to pavement base courses. Pervious concrete was developed at laboratory level, and the compaction methods, field moisture content, and fundamental properties when the material was constructed in the field were studied. METHODS : Field-applied pervious concrete was compacted at different levels using a tandem roller, and cores were taken to investigate the compressive strength, infiltration rate, continued porosity, and freeze-thaw resistance. In addition, the optimum field construction and quality control of the moisture content of a batch plant were measured. RESULTS : The moisture content of pervious concrete has an essential effect on workability and quality control during field test construction. From the test herein, the optimum value at a batch plant was found to be approximately 2.5±0.1%. The compaction level is also a crucial parameter at construction sites because it affects the mechanical and penetration properties. Considering both compressive strength and drainage, the recommended compaction was three times the round trip when a tandem roller was used. The penetration coefficient was 0.88 cm/sec when applying three times the round trip of the tandem roller. The freezing and thawing weight loss rates of the applied pervious concrete satisfied the required condition of 14% or less, regardless the compaction level. CONCLUSIONS : With the suggested mixed proportions of pervious concrete, the recommended compaction was three times the round trip of a tandem roller and a moisture content of approximately 2.5±0.1% from a batch plant. When these conditions were satisfied, the mechanical and drainage properties satisfied the required criteria.

PURPOSES : In this paper, problems and improvements in pavement marking standards are proposed as a result of the analysis of domestic/foreign standards and field data. METHODS : In this study, the US FHWA and all state standards were analyzed and domestic pavement marking standards were compared and analyzed. In addition, national highway marking test data, namely the Yeoncheon Test-Bed data, and data from Hawkins et al. (2015) were analyzed. Based on this, problems and improvements in the Korean pavement marking standards are proposed. RESULTS : As a result of literature and field data analysis, various problems were found in the Road Traffic Act and National Police Agency manual. In this standard, there is no definition of Qd; the RD reference value is set too low; and the RW and RR reference values are difficult to be considered reasonable values. CONCLUSIONS : There is an aspect in which the standard items and values of pavement markings are set under some policy judgment. Therefore, it is necessary to properly revise the standards, considering technical and economic aspects.