A discussion of reflected solar spot glare, based on research in Seattle, is pre· sented. The topics discussed include the causes of reflected spot glare, when and where it is most likely to occur, how it can be predicted, how it can affect the vision of motorists and thereby pose a threat to the safety of the driving public, and how it can be avoided through sensitive environmental design. One factor that makes reflective spot glare a potential traffic problem is that unlike the sun, which we are generally accustomed to in the sense that we know its location in the sky, solar-caused spot glare is often visible where one least expects it, creating a surprise reaction for the unaccustomed viewer. Such im· pacts are often not easily mitigated and (because an offending structure may have a life expectancy of 50 years or more) should be considered long lasting. Experience in Seattle, Dallas, and other cities indicates a growing problem, with nationwide implications, due to the use of new, highly reflective building materials. By graphically depicting patterns of reflective spot glare during certain periods of the year near potential or suspected trouble spots such as heavily traveled urban arterials, one can predict fafrly accurately the potential for adverse glare impacts, their duration, and their intensity before buildings are built. The Seattle study stresses that the solution is not to prohibit the use of highly reflective building materials but rather to ensure that they are installed or applied in such a way as not to create visible glare within the driver's task· oriented cone of vision.

Glare is a problem nearly all of us experience to one degree or another on a daily basis. The problem this paper addresses is solar-caused glare given off by specular surfaces, which can adversely affect the vision of motorists and thereby pose a threat to the safety of the driving public. Examples of such surfaces include bodies of water, shiny surfaces such as chromed car bumpers or window trim, and, lately, reflective coated glass that is used on the exterior of buildings. Although disabling solarcaused spot glare from these surfaces can be reduced for motorists--by using matt rather than glossy surfaces and highway alignments that help direct the motorist's line of sight away from sunlight reflecting off waterways and other highly reflective surfaces--it can never be fully prevented.