# Predicting Traffic Sign Retro-Reflectivity Degradation Using Deep Neural Networks
## 3 Study Area and Data Collection  
Field survey for sign retro-reflectivity data collection was conducted along selected segments of national motorways M-1 and M-2 near Islamabad-the capital city of Pakistan. The main purpose of selecting this section was to maintain similar ambient weather conditions. However, traffic volume for both the motorways were different as was evident from the amount of dust deposited on the surface of the signs. The mean summer temperature in the study area is approximately 41 C, with an average rainfall of around 90 mm while the average winter temperature is around 12 C. Figure 1 shows the study area in its entirety. Sign retro-reflectivity measurements were obtained using handheld calibrated Retrosign retro-reflectivemeter, also known as GR3. The instrument enables single-handed operation and has single-touch controls, which allows the operator to work easily with the device. The instrument works on the principle of light retro-reflection. When the equipment is placed in contact with the sign surface, a beam of light from an internal light source falls on the sign surface and reflects back and is recorded. The retro-reflectivity value (\(R_{A}\)) is then automatically displayed on a digital screen by computing the ratio of light reflecting back to the original intensity of light hitting the surface. Typically, \(R_{A}\) value is expressed in units of candelas per lux per meter squared (cd/lx/m\({}^{2}\)). Before the start of the experiment, the instrument was calibrated using the provided calibration kit. The detailed procedure for survey field traffic signs using GR3 can be found in internationally recognized standards such as ASTM E 1709, ASTM E 2540, AASHTO M 268, and EN 12899. At the start of the field measurements, sign surfaces were cleaned with detergents and cloth with the aim of assessing the impact of dust. However, multiple observations showed that sign cleaning improves the retro-reflectivity values only marginally (<10%). So, the study continued with uncleaned surfaces, which were later-on used for the experiments. \(R_{A}\) values were taken at observation angles of 0.2\({}^{\circ}\), 0.5\({}^{\circ}\), and 1.0\({}^{\circ}\) and an entrance angle of \(-4^{\circ}\), simultaneously. The observation is the vertical angle formed between the light ray originating from the vehicle headlight and the reflected ray towards the driver. It is basically a function of vehicle headlight height with respect to the target sign. An observation angle of 0.2\({}^{\circ}\) simulated the driving condition of small vehicles (such as passenger cars), and an angle of 1.0\({}^{\circ}\) replicates the night-time travel conditions for large vehicles (such as trucks). The entrance angle designates the angle between the light beam falling on the sign surface at any arbitrary point and hypothetical axis perpendicular to the sign surface at the same  
Figure 1: Study area (from Google Maps). point. The entrance angle increases with the decreasing distance of the vehicle with reference to the target sign. To observe the effect of sign sheeting placement on sign visibility performance, \(R_{A}\) reading were taken at various instrument rotations/orientations, i.e., 0, 45, 90, 135, and 180 degrees. A minimum of four replicate readings were obtained for each sheeting type (with the same brand, grade, age, and color), when available. \(R_{A}\) readings were also obtained in 4 age groups, i.e., 0, 2, 5, and 10 years for signs installed in the field. An aging period of zero refers to the readings taken from fresh samples sheeting temporarily attached (for seven days) to field signs with due permission from the national highway authority (NHA). Field retro-reflectivity data for signs surveyed was then transferred to a spreadsheet. Data with incomplete and erroneous duplicate records was removed to make it ready for subsequent analysis. Tentative dates for the exact installation year of different signs along the selected road sections in the study were also obtained from NHA.