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Tunnel Lighting

Lighting for roadway tunnels is immensely technical.  The basic idea is that the artificial lighting will transition to and from daylight enough that drivers entering the tunnel can see clearly any obstructions within, and furthermore are confident enough that they don’t step on the brake at the tunnel threshold, causing a slowdown or a hazard to other motorists.  So in an ideal world, the tunnel interior would be illuminated to an equal level to exterior surfaces all the way through.  But typical exterior surfaces are 100 to 1000 times as bright as a typical interior surface, so in practice the luminances must be stepped down in a tightly controlled fashion from the brightly lit threshold to the tunnel interiors.

Above, the perpetually failing lighting as it currently exists, with the western span of the Bay Bridge beyond.

Yerba Buena Tunnel existing lighting