Lichthinder van geluidschermen. Fase 3: verdere ontwikkeling model

Purpose : In order to avoid noise annoyance of car traffic in residential areas, a lot of sound barriers were build along the motorways in the Netherlands in the last few years. These barriers can cause glaring sun reflections. Road users often complain about these reflections. TNO has performed a study on the glare due to sun light reflection in sound barriers. An model was developed in order quantify discomfort glare on basis of glare illuminance, glare angle, background luminance, and dynamic properties, such as duration and flicker frequency. An evaluation in practice showed that the model can be improved by adding parameters concerning the probability of sun and the maximum allowed time that the road users has no view on the road due to a high glare level. Methods : The sun probability is based on KNMI hourly climate data of five weather stations in the Netherlands over the period 1979-2008. The average probability was calculated that the sun shines during daytime, as a function of time of the day, time of the year, and locations in the country. In the literature on traffic, perception and psychology we sought for publications with leads to the determination of the maximum allowed time without view on the road. Results : The probability that the sun shines during daytime and not is blocked by clouds is about one third. In the winter this probability is less than in the summer. Near the coast the shines more often than elsewhere in the country. The sun probability depends on the time of the day. At noon the probability is higher than a few hours after sunrise and before sunset. A model was developed to calculate the sun probability as a function of the month, hour of the day, and the location (coast or inland). The probability function for sunshine during the day has a trapezoidal form. From traffic safety research and guidelines for in-car system it appears that the maximum time without a view at the road should not be more than 2 seconds. A study where the natural traffic behaviour was observed, shows that time should be not more 1,8 seconds. Occlusion experiments shows that people accept a maximum occlusion time between 1.4 and 1.8 seconds, depending on driving speed, lane width, and other traffic. In case of braking cars in front or small lanes this time is shorter. From the point of view of traffic safety and acceptation of the road users we conclude that the maximum glare time should not be more than 1.5 seconds.
Conclusions : The current model for disability glare is extended with the probability of sunshine and a maximum limit of the time that the a road user should exposed to such a high glare level that makes it impossible to view the road. These extensions provide the road authorities in the future a better judgement of potential glare problems by sun reflection in existing or planned noise barriers.