Roadway Lighting
The following is taken from the "Outdoor Lighting" Chester County Planning Bulletin:
STREET LIGHTING - Typically, street lighting is under the control of the electric utility serving the municipality and they use their own design standards. For those applications that do not fall under a utility's jurisdiction, a brief description of the fixture selection and application process will be helpful.
Since roadways, highways and lanes are by their very nature long and narrow, it is only logical that the fixtures used to illuminate them would produce long and narrow beam patterns. This decidedly asymmetric beam pattern may be produced by the fixture's reflector and/or lens. In order to achieve the very wide beam spread in one direction, they are typically bright when viewed from along the axis of the roadway. That brightness might be very objectional were it not for the fact that the fixtures are most often mounted at heights in the range of 30 to 60 feet where they are above normal viewing angles. Street lighting fixtures cannot be "aimed" in the traditional sense so their house-side output must be controlled through the selection of the appropriate reflector and optical assembly (lens). Stray light and high-angle brightness can be controlled by the addition of a glare shield or baffle.
There are five street lighting fixture light distribution classifications ranging from Type I which is for narrow roads where the fixture can be located in the appropriate centerof the cartway, to Type IV for the widest roads, where the fixture is located at or off the side of the cartway. Type V produces a symmetrical pattern used to illuminate intersections.
The Pennsylvania Department of Transportation Design manual,Part II, Chapter 5,contains criteria for the design of lighting on Pennsylvania roadways. (Also see) the IES Lighting Handbook. Other design aids can also be found in some street lighting fixture manufacturers' catalogs.
Environmental Effects of Roadway Lighting
The following is taken from a technical paper by Carl Shaflik, BASc, PEng:
"Environmental impacts resulting from transportation infrastructures have been the subject of research for many years. One environmental aspect of transportation facilities largely ignored is that of light pollution. In many areas light pollution has become an important aspect of both planning and design. Neighborhoods are becoming more sensitive to the stray light that is being directed towards their property and windows. Astronomers and observatories are becoming more concerned with the increase in the sky glow around urban areas."
"It has been estimated by researchers that up to 50% of all light pollution may be the result or roadway lighting. This firmly puts light pollution in the hands of traffic engineers, and it will become their responsibility to find adequate and economic solutions."
Environmental Effects of Roadway Lighting........ For complete technical paper by Carl Shaflik
