Retroreflective color plates are important carriers for transmitting retroreflective chromaticity, and they can be used to calibrate portable retroreflection colorimeters. Measurement errors in the chromaticity measurements of retroreflective color plates create uncertainty of the retroreflective chromaticity coordinates. To study the uncertainty in the measurements of retroreflective chromaticity plates, we analyzed the uncertainty sources and evaluated the uncertainty of the chromaticity coordinates of a retroreflective color plate measured using a remote spectrum measurement system. The results showed that for a confidence probability p = 95% and coverage factor k = 2, the expanded uncertainties of the chromaticity coordinates of the retroreflective color plate, U(x) and U(y), were both 0.01. The evaluation results showed that the uncertainty of the spectrometer contributed to the uncertainty the most, mainly because the large uncertainty components arose from the measurements of the retroreflective color plate and the standard white plate.
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.
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.
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.
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