In order to improve the visual guidance in night-time traffic, major roads in the Nordic countries are equipped with delineator posts. Those posts will probably improve the driver’s comfort, but it is more uncertain how speed, and thereby accident rates are affected. The delineator post regulations are designed to improve the visibility of the road in headlight illumination. However, the regulations are not based on knowledge; it is not known which visibility the retroreflector of the post should have, neither how the posts should be arranged along the road to give the drivers the necessary information about the road ahead. The driver’s perception of the road must promote a safe and correct behaviour. In today’s regulations there is nothing about the driver’s needs versus delineator post configuration. Furthermore, the regulations in the five Nordic countries are not harmonized. As an example the distance between two posts is 100 metres in Denmark, while it is 50—60 metres in the other countries. Both costs for investment and maintenance are related to delineator posts. Therefore, it is of importance to use the posts in a correct way and amount; the cost must be justified by the benefits in terms of traffic safety and comfort. Therefore, an important question to answer was how the road should be equipped with the delineator posts. Which distance between two posts should it be on straight parts of the road and in curves? Another aim of the study was to investigate the relationship between speed and visibility of the reflectors. One hypothesis is that long visibility distance, i.e. good visual guidance, will result in high speed, which will cause more serious injuries compared to lower speed. A third aim was to evaluate the results from the VTI simulator, by measurements of real traffic. That is, this aim concerned whether the simulator results are repeated on the real road. The results show that the slowest speed was found in the condition with the poorest visual guidance, the condition with no delineator posts. Furthermore, in this condition the number of braking was approximately half of the braking in the other conditions. Delineator posts along the road, also on straight parts, mean an increase in average speed of approximately 12 km/h. Most probably this means that the severity of injury will increase, but whether the number of accidents will be influenced is difficult to predict. The investigation of relationship between visibility distance and speed showed that a visibility distance of 400 metres entailed a large speed variation: very high speed on straight parts of the road and considerably lower in curves. The conclusion from this study is that there is no reason using reflectors showing visibility distance higher than 100—200 metres in headlight illumination. Furthermore, with delineator posts in curves only there was better speed adaption to the curves. However, a questionnaire indicated that the drivers prefer delineator posts all along the road. The evaluation of the simulator study at VTI showed a small deviation between the speed on the road and the speed in the simulator. A large deviation was found in the condition without delineator posts: in this condition speed was higher on the real road than in the simulator. This fact may be explained by the visual guidance from the surroundings, which may have significantly contributed to the visual guidance on the real road, but not on the simulated road. It is reasonable to recommend a configuration similar to that one in Denmark (100 m between posts) with reflector visibility distance of 100—200 metres. This configuration results in lower investment and maintenance costs, but gives the same driver behaviour as other configurations using shorter distance between the posts. (Author/publisher)
Abstract