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.
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 R<sup>2</sup> 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.