The national technical specifications existing for road markings today include minimum performance levels on essential parameters (daytime and night-time visibility and skid resistance). It is desirable that the demands are based on both the driver's need of visibility and on what is possible to achieve with road marking. Road markings are in reality "traffic signals" which can be expected to have an impact on traffic safety, accessibility and comfort by guiding the driver along the road. Therefore, there has to be a scientific basis for answering the most relevant questions concerning design and use of road markings, such as: - What visibility distance does a road marking of a certain type and quality have? - What is the visual demand of the drivers, concerning road markings? The results from COST 331 give a scientific method for deciding the design of longitudinal road markings. This gives the necessary basis allowing research, industry and road traffic engineers to improve the road markings regarding the need of the drivers. The research programme, designed and approved by the COST 331 Management Committee, included the following phases: - 1. A review of the current use of road markings in Europe. - 2. An investigation of the visibility of road markings in a driving experiment. - 3. A study of the driver's need for visibility distances in a driving simulator. - 4. Registration of drivers' (test persons') behaviour in real traffic conditions by using an unobtrusive instrumented car. The results show that almost all countries have regulations and technical recommendations specifying geometry, design and colour of road markings. However, the road marking design varies between the countries. Also, in some countries the use of road markings made for improving the visibility in wetness and rain is prescribed. The difference between the regulations in different countries could be due to lack of a scientific base.