Study of technical parameters of experimental traffic signs — results obtained within the frames of RID 4F research projectRafał Lusa, Paweł Skierczyński, Leszek Kornalewski, Adam Czyżewski, Barbara Rymsza and Dariusz LitwinMATEC Web Conf., 231 (2018) 02007DOI: https://doi.org/10.1051/matecconf/201823102007