Institute of Transportation Engineers Safety and Operational Effects of Geometric Design Features for Two-Lane Rural Highways Workshop May 2009 Geographic, Environmental and LED Surface Conditions Based on Literature Review Edward R. Stollof Institute of Transportation Engineers December 14, 2010 Session 1 – Introduction and Background

Northern Tier US and Canadian locations Geographic Northern Tier US and Canadian locations Example: Rapid City, South Dakota: The City typically has strong winds and a significant amount of snow during the winter. The LED modules have a tendency to get covered by snow/ice build-up.

Environmental (Weather) “The Perfect Storm” Wind Direction, driving snow horizontally into the LED signal lenses Strong Humidity and moisture presence of significant moisture content in the snow to make it stick- -dry snow does not really affect the LED traffic signals operation wet, sticky type of snow

Environmental (Weather) “The Perfect Storm” Temperature Must be below freezing Snow Significant amount Conclusions This combined weather condition (The “Perfect Storm”) does not occur very often. When it does, it usually only affects signals that are facing the wind. 

LED Traffic Signal Module Surface Older-style lenses: Some of the older-style LED lenses have a much rougher surface, which can collect snow more easily.  Newer style lenses: With an LED bulb behind a smooth lens, they are less susceptible to snow collection

Yakima, WA: Traffic Signals are 50% obscured by snow