# Temporary Road Marking Paint for Vehicle Perception Tests
## 5 Discussion
While permanent paint does not significantly deteriorate in terms of visibility, it causes phantom tracks when removed using milling due to damage to the pavement as well as paint residue. In proving ground operations, where patterns need to be changed frequently, this constant alteration process including milling would eventually result in a test track full of phantom tracks. Samples 3 and 4 of the water-soluble paint caused a change in the reflectivity of the asphalt when removed, even though the asphalt did not appear damaged to the human eye, indicating faint phantom tracks that might fade over time. The main drawback of this material is its lower consistency in visibility which decreases the reproducibility of tests and requires frequent renewal efforts. Hence, the water-soluble paint is mainly recommended for test drives of a few days with low precipitation for which edgy road marking shapes are required. An important criterion not listed in Table 3 is the realism of appearance to camera- and LiDAR-based perception systems. It is not listed because this evaluation requires more research and is dependent on the specific sensor in scope. The road markings applied in a proving ground should realistically represent road markings from public roads; however, road marking materials on public roads differ based on legal requirements, region, manufacturing procedures, availability, use cases, expected overruns, maintenance concepts, budgets, and weather. Additionally, the visibility of road markings on public roads changes over time due to weather and overruns. Hence, there is no clear specification for the realism of road markings. Different indicators characterizing road markings can be found in the published literature [36]. In theory, a statistical analysis could be conducted to identify the most prevalent types of road markings on public roads; however, the most prevalent types of road markings are not necessarily the ones that are the most challenging or relevant for automated driving systems. Due to these reasons, we based our investigation on the minimum requirements found in standards for public roads [6; 7; 8; 9]. Common permanent road marking, such as high-solid paint, is manufactured and certified for public roads. Therefore, it realistically represents new road markings. Similarly, the temporary tape used in [5] is eligible for the use on public roads. Both materials can therefore be classified as realistic. The temporary water-soluble paint investigated in this study is not recommended for use on public roads due to its low durability and visibility after a few weeks. For LiDAR sensors to recognize road markings, a reflectivity higher than the surrounding pavement is essential [37]. For standard camera sensors, a noticeable contrast between the road marking and the pavement is required [13]. Sufficient reflectivity can be reached with water-soluble paint by using glass beads, which are also commonly used on public roads to increase the retroreflectivity of road markings [23]. Hence, we expect that the road markings with temporary paint will be visible for LiDAR sensors \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Criterion**} & \multicolumn{4}{c}{**Alteration Method**} \\ \cline{2-4}  & **Permanent High-Solid-Paint** & **Tape According to [5]** & **Special Water-Soluble Paint** \\ \hline Application efforts for straights & medium & medium & medium \\ and curves with radii \% 10 m & medium & medium & medium \\ Application efforts for edgy road & low & high & low \\ marking patterns & low & high & medium \\ Consistency in visibility & high & low & high \\ Difficulty to ensure reproducable & high & low & high \\ appearance & high & high & low \\ Resistance to rain and overruns & high & low & low \\ Removal efforts & high & low & low \\ Risk of phantom tracks when removed & high & low & low \\ Risk of pavement damages after removal (change in macro texture) & high & low & medium \\ \hline \hline \end{tabular}
\end{table}