http://worldcat.org/entity/work/id/5679399

Tunnel lighting design procedures

Tunnels commonly create bottlenecks in traffic flow because of a change in cross-sectional width and a discontinuing of road shoulders past the portal. The effect of these restrictions can be congestion and high accident rates unless an adequate lighting system is provided to reveal the locations of walls and curbings. The problem is most accute in daytime, when drivers make the transition from a brightly illuminated exterior roadway to the tunnel interior with a much lower luminance level. To facilitate the design of a lighting installation which will allow for this transition, it is convenient to consider tunnels as being made up of 5 zones: 1) the approach zone, 2) the threshold zone, 3) the transition zone, 4) the interior zone, and 5) the exit zone. Each of these zones has specific lighting levels and lengths depending on the tunnel wall materials, tunnel dimensions, wall color, portal landscaping, and traffic characteristics. Luminance requirements can vary from 100 fL to 250 fL depending on the tunnel orientation with the sun.

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