Evaluating mobile vehicle-mounted retroreflectivity systems against handheld measurements

Traffic signs are essential for road safety, and a key part of ensuring this is that the material has enough retroreflectivity to guarantee visibility at night. Standards such as UNI EN 12899-1:2008 specify minimum retroreflectivity requirements and periodic monitoring. Traditionally, retroreflectivity level is measured using handheld retroreflectometers, but this approach is slow, exposes operators to traffic risks, and only samples a limited number of signs. A mobile vehicle-mounted system has been developed to address these limitations, allowing large-scale data collection at traffic speed. There is a lack of studies comparing vehicle-mounted retroreflectivity measurements with handheld measurements of road signs, despite their importance for roadway maintenance and safety. This study addresses this gap by comparing retroreflectivity coefficients obtained from manual handheld measurements (ZEHNTNER ZRS 6060) and automatic mobile measurements (VISUALISE–Euroconsult system) on the same set of vertical road signs along highway sections in Bologna, Italy. The analysis provides insight into the correlation between the two measurement approaches and their relevance for evaluating the sign condition. Statistical analysis showed a reasonable correlation between the two methods, with a value of R2 = 0.504 for measurements. Results indicate that the mobile system systematically reported higher retroreflectivity values than handheld devices, with a mean bias = + 24.79 cd lx−1 m−2 and identified a larger proportion of accepted signs with 91.1% and 79.8% for mobile vehicle-mounted and manual handheld, respectively. Handheld measurements provide precise point readings, while mobile systems capture a broader, driver-oriented view of sign visibility and enable large-scale network coverage. These operational differences support their complementary roles in retroreflectivity assessment. The findings indicate that mobile measurements can support more efficient network-level screening and contribute to more reliable traffic sign asset management.