Depending on the retroreflective distribution measuring device, three sets of controlled experiments were designed. To obtain the retroreflective distribution of road traffic markings, the coefficient of retroreflected luminance (RL) changes of road traffic markings under different measurement geometry was analyzed. Several observation angles commonly used in retroreflection measurements were selected. The deviation range of vertical entrance angles was set to 8°. The horizontal entrance angles were selected according to the horizontal measurement angle of a mobile retroreflectometer unit. A white road traffic marking sample, which measured 10 mm × 46 mm, was used in the experiments. The results showed that the retroreflective distribution of road traffic markings was not uniform, the influence of the change of observation angle on the RL was greater than the entrance angle, and the change of retroreflection in the direction of the vertical entrance angle was more obvious than the horizontal entrance angle.
Retroreflective sheeting dramatically increases the visibility and conspicuity of traffic safety facilities at night. Chromaticity is an important property of retroreflective sheeting, but there are few methods and tools for measuring retroreflected chromaticity coordinates of retroreflective sheeting in China. In this paper, measurement methods are introduced and the accuracy of portable equipment is analyzed. A spectroradiometric retroreflectometer system of the National Center of Metrization for Equipments of Roads and Bridges (NCMERB) and various portable equipment of testing agencies were selected. All instruments measured the chromaticity coordinates of the same set of samples. The data of the spectroradiometric retroreflectometer system were taken as the reference values and those of portable equipment as the comparison values. The results showed that the measurement deviations of a RoadVista 932 retroreflectometer were relatively small and that it can measure retroreflected chromaticity coordinates of retroreflective sheeting. The illuminating-viewing conditions may have little effect on the retroreflected chromaticity coordinate measurement results of yellow and red retroreflective sheeting.
In a dark channel of more than 15 m, a standard A light source was used to simulate a motor vehicle's headlight, and a Nikon D750 digital camera was used as a light receiver. While the observation angle α was 0.33°, the entrance angle component β1 was −4°, the entrance angle component β2 was 0°, and the coefficients of retroreflection of the retroreflectors were measured. The entrance angle component β1 changed from −4° to 0°, and the chromaticity coordinates of retroreflectors were then measured. Experimental results show that the maximum measurement error of the coefficient of retroreflection is −2.09%, and the measured results of the chromaticity coordinates meet the national standard of retroreflective sheeting for traffic control. Obviously, the RAW data output from the camera has a linear association with the luminous flux on the surface of retroreflectors, which can be used to calculate the coefficients of retroreflection and the chromaticity coordinates.
Retroreflective traffic markings are frequently used on roadways to provide guidance to drivers as supplements to regular markings. Portable retroreflectometers are widely used to measure the photometric characteristic of retroreflective traffic markings at present. Portable retroreflectometers include an internal light source and photoreceptors. It is based on the substitution method. Substitution relies on the use of calibrated reference plate. The traffic marking has a low coefficient of retroreflected luminance. It is difficult to measure the coefficient by direct measurement method. The direct measurement method cannot assign measurement values to the reference plates. The paper proposes a new measurement method to solve the problem of measuring the photometric characteristic of the retroreflective traffic marking. It is called the expanded direct luminous intensity method, and it is different from the four methods in JT/T 690 Test Method for Photometric Characteristics of Retroreflectors. The expanded direct luminous intensity method based on CIE angular reference system. A calibrated standard source A illuminates the specimen at a distance of 15 m from the specimen. And a calibrated low-light illuminometer is used to measure the retroreflectivity of the specimen. The paper built a standard system according to this method. The measurement uncertainty of the system is 3.1% while k is 2. After comparing with several different kinds of portable retroreflectometers, the results were satisfactory. Studies have shown that this method and standard system can not only calibrate the reference plates, but also measure the photometric characteristic of retroreflective traffic markings specimens.
KEYWORDS: Roads, Distance measurement, 3D modeling, Standards development, 3D scanning, Manufacturing, Safety, Laser applications, New and emerging technologies, Line scan image sensors
Pavement texture has great influence in terms of road safety. Until recently, laser distance measuring technique that can measure pavement texture depth has become available. Compared with the volumetric patch technique which are now widely used, the laser distance measuring is a relatively new technology. This method has certain applications in the world. Through a large number of experiments, the researchers found that the accuracy of many instruments has not been high enough to fulfill the requirement. Local anomaly is the main factor of the accuracy in the distance measurement. This paper presents an improved self-correct algorithm for texture depth. The objective is to analyze the improved self-correct algorithm used in vehicle bearing road laser texture-meter for pavement texture depth evaluation carried out under ordinary testing conditions, referring to the Chinese standards in pavement texture depth. All pavement texture measurements were performed on four selected road pavements with different texture depth. The novel approach obtained a complete and consistent three-dimensional model representation from road surface scans, using three-dimensional line-scan technology. The four selected road pavements measured with 100 vehicle bearing road laser texture-meters respectively. The improved self-correct algorithm was applied to a vehicle bearing road laser texture-meter. The improved self-correct algorithm reduced the indication error of the general algorithm. The manufacturers can adjust the parameters according to the result, so that it can improve the reliability of the instruments.
Texture depth is defined as the deviations of the road surface profile from the datum plane. It is currently assessed by two methods--sensor measured texture depth (SMTD) and sand patch method (SPM). Many researchers did lots of experiments to study the correlation between these two methods, but ignored the waveform characteristic of the road surface profile. A mathematical model of the road surface profile was built in this paper to calculation of texture depth and compare the two methods. This paper studied the statistical relationship between sensor measured texture depth and sand patch method in different waveform characteristics, and found out that the frequency is the main factor. The results show that the two methods have excellent correlation at the same frequency, and the correlation coefficient R2 is equal to 1. Plates with same frequency were designed to conducted comparison experiments. The result verify the above conclusion. It shows good correlation between the laser detection technology and the volumetric patch technique. Since manufacturers mainly use sand patch method for experiments, the result provides a theoretical basis and technical support for factory inspection. Also, it can be used to get the characteristics of the pavement structure in return.
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