A study into the nature of elements that are insufficiently visible during driving at darkness on motorways was performed. Eight subjects drove a total of 32 rides of 243 km on Dutch motorways. During driving, their comments were recorded on items that were either not seen clearly enough or were seen too late for safety. The driving conditions and location of the items commented on were also recorded. The most frequent visual problems related to geometrical road characteristics (lane boundary, course of road, place of exit). Remarks on the visibility of other traffic were rare and nearly always related to defective car lighting. Obstacles on the road were even more infrequent. On soaking wet road surfaces, the number of visual problems per km were four times higher than on dry roads. Public lighting halved the number of problems. Busy traffic did not cause a higher frequency of visual problems. It appeared that public lighting is especially effective for decreasing glare and confusion caused by building and vehicle lights. Public lighting also decreased problems with seeing geometrical road characteristics, but to a lesser degree. It is inferred that modern road marking material and delineators, which maintain their reflecting quality during wet weather, seem to be the most efficient means for improving the visibility of geometrical road characteristics. Public lighting appeared to play a minor role in improving the visibility of obstacles and traffic participants on motorways. Therefore the level of public lighting on express highways may be considerably less than those stipulated in current CIE recommendations.
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