The final purpose of COST 331 is to establish an up-to-date scientific method with which, on the basis of drivers' visual needs, to determine the optimum pavement marking design in order to ensure that markings are visible, by day and by night, in all weather conditions. At present, most research in this area, both national and international, concentrates on: Development of new marking products which meet the above mentioned requirements for as long as possible (maximum functional life), and Design of new technologies for the manufacture of high-performance equipment for assessing those requirements. Scientifically validated uniform criterion are therfore needed for the appropriate design of road markings in order to provide the following "benefits" to different users: For drivers: Optimisation of the cognitive load; Achievement of visual guidance by day and night in all weather conditions. For road authorities: Availability of a scientifically validated methodology for designing road markings; Maximisation of the cost-effectiveness of road markings. This work has been confined to longitudinal road markings (of two types: conventional and those designed to maintain night time visibility in adverse weather conditions) including directional arrows. The colour of road markings is not considered itself as a variable to be included in the different experimental phases.