The required lighting level in the entrance zone of road tunnels is determined by two main factors: (a) the perception of objects in the tunnel from outside and within a safe stopping distance, and (b) the prevention of the black-hole effect, which can lead to unexpected changes in driver behaviour. Detailed analysis of the visual task of object perception shows that counterbeam lighting produces significantly enhanced object visibility because of the high contrast generated. This effect allows a much lower luminance level compared to symmetric lighting. In addition, the luminance yield on the road is much higher for r3-type road surfaces. Compared with conventional symmetric lighting, a substantial saving of energy can be achieved. The requirements for the luminaries and lighting design, the photometric values of counterbeam lighting attainable in practice, and the critical points associated with it are discussed in detail. The conclusions stemming from this discussion and the present experience with counterbeam lighting in switzerland demonstrate that with this lighting system a high-quality alternative for tunnel entrance zone lighting is available. This paper appears in Transportation Research Record No. 1287, Traffic flow, capacity, roadway lighting, and urban traffic systems 1990.
Abstract