When light makes the difference As Australia’s population increases and governments endeavour to limit urban sprawl via consolidation of our cities and suburbs, congestion on our road networks is building. In turn, reliance on tunnels and underpasses to improve traffic flow is set to continue. Why do we need Tunnel / Underpass lighting? To ensure drivers can approach, pass through and exit the tunnel or underpass with a degree of safety commensurate to that of the approach road. Unlike an uncovered road the approaching driver’s adaptation level is significantly higher in comparison to the lighting level within the tunnel and therefore limits the driver’s ability to view the road surface, surrounds and other objects. This phenomenon is generally known as the “black hole” effect. How much light is required? In principle, the lighting level required within the tunnel entrance (threshold zone) is determined by the luminance at the portal. After the threshold zone the lighting level within the tunnel or underpass is gradually reduced in unison with the driver’s adaptation level. Best practice approach To date, Australia’s major tunnel installations have incorporated a best practice approach, where basic daytime and night-time lighting is achieved with a continuous row of fluorescent luminaires installed throughout the entire length of the tunnel. Supplementary boost lighting is then provided at the entrance, transition and exit zones to cater for changes in ambient light levels throughout the day. The benefits of this system are excellent visual guidance, uniform appearance and minimisation of annoying flicker and glare. This approach is now changing due to the higher capital and maintenance cost of a continuous lighting system in comparison to a discrete lighting solution. Whilst a discrete system provides significant savings in capital and maintenance and therefore is desirable from a cost point of view, there are a number of challenges to overcome at the design or specification stage. Apart from compliance to the nominal lighting technical parameters designers need to consider the overall visual effect as well as other factors to ensure the long term success of this type of installation.
Exit Zone
Access Zone
Threshold Zone
Transition Zone
Interior Zone
EXIT
ENTRANCE
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