## 3 Materials and Methods  
### Data Description and Data Pre-Processing  
Two datasets were used in this study; the first one was collected in Sweden and the second one was collected in Denmark. Generally, the weather conditions and sheeting materials are almost identical in both countries. The Road and Transport Research Institute (VTI) in Sweden collected the data from randomly selected signs mounted in the Swedish Transport Administration's West and Mid regions, with examples shown in Figure 2. The purpose of the collected data (VTI data) was to analyze the life cycle costs for road signs. The selected road signs were equally distributed between the northern and southern parts of Sweden. Only road signs on the right side of the road in urban and rural areas were investigated. Since road traffic signs can be in stock and the year of manufacture can thus be earlier than the year of installation, the inventory of four location signs was carried out. The selected location signs were manufactured to order and were thus set up soon after delivery. Stop signs were also investigated in VTI data to analyze the red retroreflective material. The NMF group, a voluntary Nordic research cooperation, measured 10 \(\times\) 10 cm reflective sheeting samples (shown in Figure 3) which were mounted on a test stand and placed on the roof of the Danish Technical University, at its campus in Rise. The datasets were cleaned of incomplete and unnecessary data, such as the manufacturer's name and description of the surrounding environment, because these data were not suitable for this study. The relevant features that remained after cleaning are listed in Table 2.  
Figure 3: Reflective sheeting samples in the NMF data. Figure 2: Randomly selected road signs in VTI data. The coefficient of retroreflection (RA) was measured in cd/lx/m\({}^{2}\) at an observation angle of 0.33\({}^{\circ}\) and measuring angle of 5\({}^{\circ}\). In this study, the coefficient of retroreflection is named retroreflection, which is the coefficient of luminous intensity of a plane retroreflection surface to its area, or a ratio of the returned intensity to incident illumination divided by the area of the retroreflection [1]. Daylight chromaticity (X, Y) was measured according to the CIE color space system. The luminance factor (\(\beta\)) is the ratio of the flux reflected from a specimen relative to the flux reflected from a perfect reflecting diffuser under the same geometric and spectral conditions of measurement. B is used to measure the brightness of the material and ranges from 0 for perfect black to 1 for perfect white. This work investigated five colors: blue, green, red, white, and yellow  
At the same time, three different types of retroreflective sheeting were included in both datasets (Class 1, 2, and 3). The main difference between the classes is the amount of reflected light by each sheeting, with Class 3 reflecting the most, as described below:  
* Class 1:  
Three different sheetings belong to this class. The first one is Engineer Grade (EG) sheeting that has glass beads as a reflective material and it represents the least reflective type of foil. The second one is the Engineer Grade Prismatic (EGP) that has prisms instead of glass beads as reflective material. The last one is the Super Engineer Grade (SEG), which is similar to the Engineer Grade but with less variance in the size of the glass beads. * Class 2:  
High Reflectivity (HR) or High Intensity (HI) has glass beads as reflective material, but the encapsulation of the beads is of a different type, which gives the reflected light a narrower beam. * Class 3:  
Diamond Grade (DG) is a highly reflective prismatic material. Finally, the direction in degrees gives the azimuth angle to which the sign is facing, where north, east, south, and west are 0, 90, 180, and 270 degrees, respectively.