Snow and Led Traffic Lights

Lynne Kiesling

The snowy weather across much of the northern hemisphere this week is being disruptive in many ways. At the Freakonomics blog, Eric Morris highlights one unanticipated and unintended disruption — snow obscuring energy-efficient LED traffic lights:

The biggest weakness of LEDs is their biggest strength – they don’t radiate much heat. What on earth could be wrong with that? Depends on which part of the earth you inhabit. In the upper Midwest, LEDs can have deadly consequences.

LEDs’ energy conservation creates a problem in case of a – literal – perfect storm. Low temperatures, wet snow, and driving wind can coat – and obscure – traffic signals. Traditional bulbs throw off heat which melts the snow. LEDs don’t. The result is intersections without visible traffic lights which are hazardous and sometimes deadly, as was recently the case in Chicago.

The principal tradeoff in this example is between energy efficiency/cost/environment and safety while driving. I hope that one of the commenters is correct and that there are straightforward engineering approaches to minimize this tradeoff. My initial thought was downward-slanted shields around each light, both to keep the snow off of the light directly and to take advantage of gravity to prevent the snow from accumulating on the fixture.

6 thoughts on “Snow and Led Traffic Lights

  1. The shield probably wouldn’t work in areas that receive wet snow. Here, in Michigan’s Upper Peninsula, we get dry lake effect snow. But in much of the country, the heavy stuff would likely coat and stick to the shield.

    Somebody might claim a case for creating, manufacturing, distributing and attaching the shields. It would allegedly create more jobs.

  2. But if it coats and sticks to the shield, that still doesn’t obscure the light, right? It may focus and tunnel the light, but not obscure it. Here we get both wet and dry snow, lucky us …

  3. Traffic lights are frequently but not always shielded, right? So it should be an easy matter for someone to compare LED with and without shielding to see if it solves the problem. Alternately it does seem easy enough to engineer a solution which adds a small heating element that triggers only at below freezing temperature, or if smarter only if below freezing temperature and precipitation, or only if the light is obscured by snow/ice.

    But of course the analysis requires comparing the costs of these solutions, and the energy saved by LED signals + smart heating, to costs of non-LED signals or other approaches.

  4. Interesting that it takes until the very end of the article to acknowledge that the driver is really at fault. When the power goes out does that give you the right to ignore an intersection? Of course not! Might be time for some Verkeersbordvrij.

  5. Steve, thanks for the reminder! I *knew* I had seen a comment on it back in December, but I couldn’t for the life of me remember where and from whom!

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