Sometimes it Snows on Traffic Signals
Ever since traffic signals were invented, the bulbs within not only produced light, they also produced heat. And although no one thought much about it at the time, this heat, quietly and without fanfare, kept traffic signals snow and ice-free.
Incandescent bulbs were used in traffic signals — 150 watts for the red light and 137.5 watts for the green and yellow lights (yep, you read that correctly, 137.5 watts — all I know is these optimal color/wattage combinations were the result of a very long and expensive scientific study having something to do with the absorption of radiant energy).
Fast forward to the present and the efficiency of LED lighting replaced incandescent lighting just about everywhere. And it was during the heat of the summer, that someone realized LED lights could be used for traffic signals. They last longer and need less energy, “Let’s do it!” Again, keep in mind this epiphany occurred in teh summertime when the light bulb replacement crew was replacing traffic signal bulbs (the bulbs had to be replaced every two years — and guess how many men were on the light bulb replacement crew — let me just say that ladder can hold more than one person).
Because it sometimes snows on traffic signals in Indianapolis (yep, just like the song), something had to be done. LED’s were saving a lot of energy but not doing a very good job at melting snow — unlike incandescent bulbs, they don’t “waste” energy by producing heat. Here are some things that were tried:
● Changing the shape of the lenses
● Experimenting with different visors
● Special lens coatings
● Heated wire embedded in the lens (akin to the resistance wires printed on your car’s rear windshield)
● Using a heatsink to leverage the small amount of heat that LED’s produce
● Thermostatically controlled mini-heaters designed to replicate incandescent bulbs
Of course, in a sense, the above measures are all interim — autonomous cars won’t need traffic signals. Until then, drive safe, and Happy New Year!
Chet Skwarcan (traffic engineer, author, unique insights) with over 25 years of traffic engineering experience — online help available at TrafficEngineering.com/Services