MERCURY LIGHTING FOR A TUNNEL

The road in the tunnel under the Welland Canal at the city of Welland, Ontario, was constructed with a synopal surface of light-reflecting stones to increase interior roadway brightness. The entrance portal of the tunnel is flared and painted with low-reflectance paint to aid eye adaptation. To aid the driver in overcoming the sharp contrast in daylight hours between the outside and the dark interior, the highway outside the tunnel was paved with black asphalt, with a change at the portal to the synopal surface. Illumination levels of 1.5 foot-candles on the roadway and 1.3 foot-candles measured inside the tunnel at night are satisfactory and prevent the shock drivers sometimes experience driving out of a brightly lit tunnel into the dark. With the mercury unit there is some variation of lighting level; however, this variation was not felt to be objectionable by any of the observers. /DOT/