• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.21 no.2
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• pp.101-115
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• 2022

This study compared the performance of LiDAR in detecting objects in rough weather with that in clear weather. An experiment that reproduced rough weather divided the fog visibility into four stages from 200 m to 50 m and controlled the rainfall by dividing it into 20 mm/h and 50 mm/h. The number of points cloud and intensity were used as the performance indicators. The difference in performance was statistically investigated by a T-Test. The result of the study indicates that the performance of LiDAR decreased in the order in situations of 20 mm/h rainfall, fog visibility less than 200 m, 50 mm/h rainfall, fog visibility less than 150 m, fog visibility less than 100 m, and fog visibility less than 50 m. The decreased performance was greater when the measurement distance was greater and when the color was black rather than white. However, in the case of white, there was no difference in performance at a measurement distance of 10 m even at 50 m fog visibility, which is considered the worst situation in this experiment. This no difference in performance was also statistically significant. These performance verification results are expected to be utilized in the manufacture of road facilities in the future that improve the visibility of sensors.

• International Journal of Highway Engineering
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• v.18 no.6
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• pp.77-85
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• 2016

OBJECTIVES : A fog generated field test was conducted to analyze the relationship between the luminance of variable speed-limit signs and the legibility distance under various fog density conditions. By using this study, appropriate luminance values can be selected depending on the density of fog. METHODS : An actual tunnel was selected as the area to conduct the test, as other places cannot maintain the fog condition because of rapid air current. Ninety-two subjects were recruited for this test, which took place during the course of three days. Visibility-distance detecting sensor was used to measure the visibility distance due to the fog density time, simultaneously with the evaluation of legibility distance by subjects. RESULTS : The test results show the relationship between luminance values and the legibility distance corresponding to the visibility distance due to fog. According to the technical test results, lower luminance value such as $7000cd/m^2$ corresponds to less legibility distance compared to higher values such as $20000cd/m^2$ or $40000cd/m^2$. However, the amount of difference between $20000cd/m^2$ and $40000cd/m^2$ is negligible in our test. CONCLUSIONS : The results of this study can be used to select appropriate luminance of valuable speed signs under fog conditions. Hence, drivers can expect to have more room to respond to adverse weather conditions, thereby reducing the risk of accidents.

• International Journal of Highway Engineering
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• v.18 no.6
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• pp.145-152
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• 2016

OBJECTIVES : Visibility at night can be improved by using retroreflection for short distances and phosphorescent line markings for long distances. In this study, we analyzed the characteristics of the phosphorescent line marking through a laboratory luminance test. Field performance analysis was performed through tests conducted on the road. We also examined the luminance measurement methods using the digital image obtained during the phosphorescent visibility evaluation. METHODS : In this study, the laboratory luminance test of the phosphorescent line marking was conducted using seven specimens to characterize the luminance changes according to the type of the glass beads, the thickness of the phosphorescent line marking, and the brightness and irradiation time of the light source. Phosphorescent and general line markings were made at 150 m to investigate the field luminance performance. A preliminary review of the luminance measurement methods was made using a digital image from a digital single-lens reflex (DSLR) camera. The measured luminance ratio of the general and the phosphorescent line markings was compared with the calculated luminance ratio using luminance analysis. RESULTS : Through the laboratory luminance test, it was seen that the change in luminance, which corresponds to the brightness of the light source, appears large but the influence of the thickness and irradiation time is low. The field performance test of the phosphorescent line marking conducted on the road involved measuring the luminance on the day the marking was made and 7 days after the marking was made. The luminance was found to be $190mcd/m^2$ at 30 min after sunset and approximately $10-12mcd/m^2$ 4h after sunset. The results of the luminance test were captured using a digital image for each time group. The luminance ratio of the phosphorescent line marking, when compared to that of the general line marking, showed a similar trend within a 13% maximum error. Additionally, when this luminance ratio is compared to the direct field measurement, it could be confirmed that the luminance ratio, as captured in the digital image, showed a similar tendency. CONCLUSIONS : 1) The change in luminance corresponding to the brightness of the light source is significant in comparison with that corresponding to the thickness and the irradiation time. In addition, the results of the field test for the phosphorescent line marking satisfied the phosphorescent fire protection standard. 2) We examined the validity of the luminance measurement method using a digital image and we concluded that the change in the luminance ratio shows a similar tendency in both the cases. The results can form the basis for luminance measurement methodology for the construction and maintenance of phosphorescent line markings.

• International Journal of Highway Engineering
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• v.14 no.3
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• pp.131-140
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• 2012

Lane markings such as edgelines, centerlines, and lines that delineate lanes generally provide drivers with the various information for safe driving. Drivers can easily recognize the lane markings through the color differences between the markings and road surfaces during the daytime. However, it is a bit difficult for drivers to perceive them during the nighttime due to the lack of artificial lights. Although the glass beads with the 1.5-refractive index have been used to improve the visibility of the lane markings during the nighttime, it is still difficult for drivers to recognize the lane markings properly, especially during the rainy nighttime, which may often lead to traffic accidents. To improve the retroreflectivity and visibility of the lane markings during the rainy nighttime, the high refractive beads with the 2.4-refractive index are essentially required, but they do not work appropriately during the dry nighttime. Thus, the mixed materials with the 1.5, 1.9, and 2.4-refractive beads should be considered for the satisfactory implementation of the lane markings. This study reveals the best mixing rates of the beads by conducting benefit-cost analysis under various weather conditions in Korea. The analysis results show that the lane markings with the 100% of the 2.4-refractive beads provide the highest visibility of lane markings regardless of the roadway conditions, but the benefit-cost (B/C) ratio of the bead mixture is merely 0.46. The best mixing rate of the beads, from the highest B/C ratio viewpoint, was identified as the mixture with a 80% of 1.5-refractive beads and a 20% of 2.4-refractive beads. Some limitations and future research agenda have also been discussed.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.20 no.6
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• pp.228-241
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• 2021

This study verified the performance change of a LiDAR when it detects road signs, which are potential cooperation targets for an autonomous vehicle. In particular, road signs of different colors and materials were produced and tested in controlled rainfall on the real road environment. The NPC and intensity were selected as the performance indicators, and a T-Test was used for comparison. The study results show that the performance of LiDAR for the detection of road signs was reduced with the increase of rainfall. The degradation of performance in retroreflective sheets was lesser than painted road signs, but at the amount of 40 mm/h or more, the detection performance of retroreflective sheets deteriorates to an extent that data cannot be collected. The performance level of black paint was lower than that of other colors on a clear day. In addition, the white sheet was most sensitively degraded with the increase in precipitation. These performance verification results are expected to be utilized in the manufacturing of road facilities that improve the visibility of sensors in the future.

• Journal of Korean Society of Transportation
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• v.14 no.3
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• pp.143-154
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• 1996

Since chevron alignment sign provides a user with information of road's alignment, it plays an important role in improving the safety aspects of the highway. Currently, it is installed without reasonable design specifications and maintained under insufficient labor and working time. This study, therefore, reviewed the current specifications involving design, installation, shape, and color and several alternatives were generated. The readibility and visibility were chosen as measure of effectiveness to compass these alternatives. Furthermore, spacing of sign was evaluated. The field study resulted that yellow background with black sign was more realible and visible than the other alternatives.

• Proceedings of the KAIS Fall Conference
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• 2010.11a
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• pp.197-199
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• 2010

우리는 CCTV 카메라 영상에서 도로상에 통행중인 차량의 이동영역이 시정에 따라 달라진다는 점에 착안하여 이동영역을 추출하고 이를 이용하여 가시거리를 계산하는 시정 측정 장치를 개발하고 있으며, 이 때 가장 중요한 것은 어떻게 추출된 이동영역을 이용하여 시정측정값을 계산할 것인가 하는 것이다. 이동영역이 추출된 이미지에서 이동영역의 상단라인을 나타내는 가시선의 위치와 시정거리와는 일반적으로 지수함수의 관계를 가지게 된다. 본 논문에서는 가시선의 위치를 이용한 시정측정을 위해 도로의 표면과 카메라의 기하학적인 관계를 설명하고 비선형 곡선적합 방법에 기초한 도로모델과 이를 이용한 도로시정 측정과 실제 적용방안을 제시하고 구현한 결과를 보인다.

• International Journal of Highway Engineering
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• v.17 no.6
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• pp.105-115
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• 2015

PURPOSES : This study aimed to evaluate the appropriateness of safety with the standard for threshold zone luminance as specified in the Recommendation for Lighting of Traffic Tunnel, which has been widely adopted worldwide. METHODS : A driving test of the subject in a full-scale road tunnel was conducted. The adaptation luminance and threshold zone luminance, which should be known for the driver to perceive an object within stopping sight distance, were obtained. These values were compared with the adaptation luminance and threshold zone luminance obtained by the existing reduced model test and tunnel lighting standard that has served as a guideline for the current threshold zone luminance standard. RESULTS : According to this study, threshold zone luminance should be increased to at least 1.8 times the value proposed in the existing studies and to twice the domestic tunnel lighting standard (KS C 3703: 2014). CONCLUSIONS : The threshold zone luminance proposed in this study differs largely from that obtained from indoor tests and from the current tunnel lighting standard used worldwide; this difference may be attributed to the fact that the indoor tests did not incorporate driving workload, non-uniformity of luminance distribution in terms of sight, and factors that reduce the visibility of the driver, such as the light reflected into the driver's eyes. Hence, it is necessary to further review the factors that reduce the visibility of drivers approaching tunnels in order to determine the rational tunnel threshold zone luminance.

• International Journal of Highway Engineering
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• v.18 no.3
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• pp.127-134
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• 2016

PURPOSES : Low visibility caused by dark surroundings at nighttime affects the likelihood of accidents, and various efforts, such as installing road safety facilities, have been made to reduce accidents at night. Despite these efforts, the nighttime severity index (SI) in Korea was higher than the daytime SI during 2011-2014. This study determined the factors affecting daytime and nighttime accident severity through a discriminant analysis. METHODS : Discriminant analysis. RESULTS : First, drowsiness, lack of attention, and lighting facilities affected both daytime and nighttime accident severity. Accidents were found to be caused by a low ability to recognize the driving conditions and a low obstacle avoidance capability. Second, road conditions and speeding affected only the daytime accident severity. Third, failure to maintain a safe distance significantly affected daytime accident severity and nonsignificantly affected nighttime accident severity. The majority of such accidents were caused by rear-end collisions of vehicles driving in the same direction; given the low relative speed difference in such cases, the shock imparted by the accidents was minimal. CONCLUSIONS : Accidents caused by a failure to maintain a safe distance has lower severity than do accidents caused by other factors.

• Current Optics and Photonics
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• v.3 no.5
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• pp.423-428
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• 2019

Visibility of road-surface markings is one of the critical issues that should be secured for self-driving cars as well as human drivers. Glass beads are taking on the role of retroreflectors, and therefore are considered a necessity in modern pavements. In this context, retroreflectance is sensitively dependent not only on the refractive index of glass beads but also on that of the surrounding medium. This implies that the optimum refractive index of glass beads immersed in water, i.e. under wet conditions, is different from that of glass beads surrounded by air, i.e. under dry conditions. A refractive index of approximately 1.9, which is known to maximize retroreflectance under dry conditions, actually exhibits much poorer retroreflectance under wet conditions. This suggests that glass beads with optimal refractive index for wet conditions need to be installed together with those for dry conditions. We propose a facile but practical model capable of calculating retroreflectance of glass beads surrounded by an arbitrary medium, here water in particular, and experimentally verify its capability of assessing the refractive index of commercial glass beads. Changes in retroreflectance according to the mixing ratio of glass beads with different refractive indices are also discussed, in an effort to propose the proper use of glass beads produced for dry and wet conditions.