Road Markings: A Review from the Conventional Functions to Smart Perspectives

Road markings (RM) consist of two layers (a paint layer and a retroreflective layer) that work together as a functional system. These elements have evolved over the years, from simple marks that contrasts with the pavement to more complex and sophisticated systems. Currently, in addition to performing the use properties, luminance coefficient under diffuse illumination (Qd) and retroreflected luminance coefficient (RL), responsible for daytime and nighttime visibility, respectively, recent research has explored the use of smart materials, achieving additional functionalities such as photoluminescence, anti-aging, self-cleaning, and thermochromism. This study presents a comprehensive analysis of the state-of-the-art advancements in both the traditional functions for which RM were originally designed and the emerging new functionalities. This includes the main concepts, the key materials used, how they perform to provide greater durability, their interaction with automated driving, and their environmental impacts. Regarding new capabilities, this work reviews the materials used, functionalization techniques, performance tests, and identifies gaps in the literature and potential future research. This review suggests that RM are continuously evolving and new developments in this field promise to further enhance road safety. For example, photoluminescent materials, already in advanced stages of development for RM, aim to improve nighttime visibility beyond RL, while thermochromic RM are in the early stages of research to function as real-time sensor for ice and snow on the pavement.