The use of artificial daytime lighting is warranted when user visibility requirements are not satisfied by the natural sunlight. Overall tunnel visibility varies considerably with such factors as geometry of the tunnel and its approaches, traffic characteristics, roadway and environmental reflective surfaces, the climate and orientation of the tunnel, and visibility objectives. Comprehensive literature is available on the technical aspects of visibility and lighting of tunnels [9]. Information on lighting levels for tunnels requires a detailed analysis of the tunnel approach characteristics. Tunnel lighting requires considerable experience to achieve proper design.
• Parking areas. The recommended average maintained lighting level is 1.0 fc (11 lx) for both automobile and truck parking areas with a uniformity of 3:1 to 4:1 over the entire area. Special areas that should have the higher levels are handicap ramps, sanitary disposal stations, and other features that require detail viewing.
• Activity areas. The major pedestrian activity areas are restrooms, information centers, and walkways to and from the buildings and the parking lot. Minor activity areas include picnic tables, dog walks, and other walk areas. The recommended lighting level for major areas is 1.0 fc (11 lx) with a 3:1 to 4:1 uniformity ratio. Minor activity areas should be lighted to 0.5 fc (5 lx) with a uniformity ratio of 6:1 [3].
Rest areas are often located in remote areas that are not readily accessible by bucket trucks or other special maintenance equipment. This requires that lighting system components be selected that provide maximum protection against vandalism and require minimal maintenance. One device that has been used to allow pole-mounted luminaires to be maintained, and lamps changed, without using a bucket truck is an individual lowering device (ILD) which allows the pole-mounted luminaires to be lowered to ground level, one at a time, for servicing. This is done with a hand-operated winch that is lightweight and easily portable by one person. One such ILD (Fig. 7.60) that has been designed to DOT requirements and used successfully is manufactured by ITS Products Inc., Dothan, Ala.
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FIGURE 7.60 Lowering device manufactured by ITS Products Inc. |
