Turk J Engin Environ Sci 24 (2000) , 119 – 126. c  T ¨ UB ˙ ITAK Parameters Affecting the Determination of the Tunnel Threshold-Zone Luminance Sermin ONAYG ˙ IL Faculty of Electric and Electronic Engineering, Istanbul Technical University, 80626, Istanbul-TURKEY Received 01.09.1999 Abstract In order to determine the level of the tunnel threshold-zone luminance, as series of visual experiments were conducted using a tunnel entrance simulator. For the experiments 110 observers were used. The results showed that the assumed parameters for the definition of the critical object and environmental conditions strongly affect the recommended luminance levels. Key Words: Threshold-zone luminance, Visual ability, Duration time, Perception probability, Safe stopping distance. T¨ unel E¸ sik B¨olgesi Parıltısının Belirlenmesinde Etkili Olan Parametreler ¨ Ozet Bu ¸ calı¸ smada, t¨ unel e¸ sik b¨olgesi parıltı seviyesinin belirlenmesi i¸cin, bir t¨ unel giri¸ sisimulat¨or¨ u kul- lanılarak bir serig¨or¨ u¸ s deneyleri ger¸ cekle¸ stirilmi¸ stir. Deneylerde 110 g¨ozlemcikullanılmı¸ stır. Deney sonu¸ cları, kritik cisim tanımı ve ¸cevre ko¸ sulları i¸cin kabul edilen parametrelerin ¨onerilen parıltı seviyeleri ¨ uzerinde¸cok etkili oldu˘gunu g¨ ostermektedir. AnahtarS¨ozc¨ ukler: E¸ sikb¨olgesiparıltısı,G¨or¨ u¸ syetene˘gi,G¨ozlems¨ uresi, Algılama olasılı˘gı, Emniyetle durabilme mesafesi. Introduction The increased volume of traffic has made the con- struction of suitable tunnels necessary. However, they are expensive. A long tunnel, when it is not lit, especially on bright sunny days, appears as a black hole for the approaching driver. In order for the driver not to lose his visual ability, and carefully taking the dark adaptation of the eye into account, it is necessary to have intensive lighting in the thresh- old (first) zone of the tunnel. If the lighting in the tunnel is at the same level as daylight, this may be a solution to this problem. When the costs of the es- tablishment and operation required to achieve such lighting are taken into account, daylight level will not be economically appropriate. If only the budget reduction is considered and a low luminance level is provided, that will disturb and hinder the visual abil- ity of drivers, and traffic conditions will become very dangerous. The engineer has to find the economi- 119