Public roads without road markings, especially roads carrying high traffic volumes, would lead to chaos and accidents resulting in injuries and loss of life. The road authorities need to ensure that all signage is well maintained and conforms to the Southern African Development Community Road Traffic Signs Manuals (SADC RTSM) (1999) and the South African Road Traffic Signs Manuals (SARTSM) (1999).
The most important aspect of road markings is that they must be retroreflective. The minimum RL for white and yellow road markings is 100 mcd/m2/lx and 70 mcd/m2/lx respectively (SADC RTSM, 1999). There are other important parameters to which road markings should conform, such as the Qd, colour and skid resistance. There are various types of road marking paints and road marking materials, namely solvent-borne, water-borne, cold plastic, thermoplastic and preformed tape applied universally. In SA, solvent-borne paints, water-borne paints and thermoplastic materials are widely used, with cold plastic materials being increasingly used of late. There are SABS standards on solvent-borne and water-borne road marking paints covering a wide range of aspects. However, there are insufficient standards on plastic road marking materials and therefore some road marking applicators could be applying inferior quality plastic road marking materials.
The only specification related to thermoplastic road marking materials published by the SABS is the SABS EN 1424:1997 (1997) (Road marking materials - premix glass beads). This specification was adopted by the SABS exactly as per the European Standard EN 1424:1997 (1997) and it specifies the requirements for laboratory tests on aspects of premix glass beads such as the granulometry, refractive index, chemical resistance, quality and surface treatment. Since the European specifications are widely adopted by many countries, the BS EN 1436:2007 (2007) specification was used in conjunction with the available SA standards in this study to develop the thermoplastic road marking standard. It is more advantageous for the road authority to stipulate the specifications with which road marking products must comply than to give the detailed specification of each constituent. It would be time consuming and costly to test each constituent, besides which the equipment to test the constituents is not readily available in SA. The onus should be on the manufacturer to ensure that the formulation of the road marking material is such that the product meets the required specifications.
The service life of road markings is affected by volume and type of vehicles passing over them, the type of road surface, sand and dirt, climatic conditions and application of the road markings. On clean roads, both asphalt and chip seal surfaces, thermoplastic road marking materials have longer RL and Qd service lives than water-borne road marking paints. The white road marking paints and materials generally complied with the colour specification. However, the yellow road markings complied minimally with the colour specification on both clean and dirty roads. Although thermoplastic road marking materials have a longer RL service life on clean roads, it might not be economical to use them on dirty roads since the RL service life was similar for water-borne road marking paints and cold plastic road marking materials. The initial skid resistance of white and yellow 1.2 mm thermoplastic complied with the specification.