0. 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

1. 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.

2. 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

3. 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. 

4. 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

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