LED Astray

Technological innovation has cut many of the trickiest environmental Gordian knots. As readers of SuperFreakonomics know, at the end of the 19th century the American city was tottering on the brink of environmental catastrophe. The cause: byproducts of transportation, specifically the horse-drawn variety (more here). Manure, flies, accidents and disease abounded, until the timely arrival of a technology which at the time was hailed as an environmental savior — the internal combustion automobile.

Of course, those who celebrated did not fully realize that the miracle technology would bring troublesome consequences of its own. Today we face the specter of global warming, to which the automobile is an important contributor.

Just like our ancestors in the fin-de-siecle city, we are using new technology to fight the shortcomings of the old. And unsurprisingly, like our ancestors, we are bound to find that our technological fixes can have unintended, malign consequences of their own.

Consider the seemingly noncontroversial replacement of conventional traffic signals with LED bulbs. What’s not to like?

LEDs last up to ten times longer than the old bulbs, saving on equipment and labor costs. They drastically cut energy consumption. (One Illinois jurisdiction found that the conversion of an intersection reduced electricity bills from over $60 per month to under $10.) Finally, LEDs are brighter than conventional bulbs, increasing visibility. Pretty cool, huh? Exactly – and that’s the problem.

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.

None of the proposed solutions are foolproof. Heating up the LEDs would help defeat the purpose of saving energy. Lights can be cleaned manually, but with about 2900 traffic signals in Chicago alone, finding, dispatching teams to, and cleaning obscured lights is a fairly big task.

We shouldn’t overstate this problem. It takes just the right conditions to occlude lights, and many times the situation resolves itself. When lights are out, motorists should know to exercise caution and treat them as if they are stop signs.

However, to this point dozens of accidents have been attributed to the LEDs. Is it worth it? Probably, but that is little consolation for those hurt and killed in these crashes.

Perhaps new technological solutions will be found, as has happened to an extent with the automobile. In the mean time, hopefully motorists in colder regions will lengthen their lives by adjusting to this new hazard. Or by moving from Chicago to LA, the way I did.

(They’d have to give up real Chicago dogs and pizza, but this would undoubtedly lengthen their lives as well. Whether a life without these delicacies is worth lengthening is another question.)

Despite the crashes, departments of transportation have no intention of giving up LEDs, any more than their 19th century counterparts would have considered giving up the internal combustion engine. As with the auto, some consequences, even deadly ones, will have to be lived with.

This may seem callous, but transportation often calls for tough decisions that involve sacrificing human life. Surprisingly, these often receive very little public scrutiny compared to more conspicuous life-and-death issues like the death penalty or the wars in Iraq and Afghanistan. More on one such overlooked transportation question coming soon.

(Hat tip: Gary LaBelle)


You know, I noticed the traffic lights near my apartment getting gummed up with snow a few times this Winter, but I never thought to attribute it to them being switched to LEDs a few months ago.


I read LED Ashtray and was quite intrigued as to what the purpose would be. Still an interesting case of unintended consequences.


I'm surprised - in fact, shocked - that you didn't do a basic cost vs. benefit analysis using statistical values of life for the US. (I think SF even throws out $7M/life but you could use a range from some of the major papers in this field.). From what I can tell, you have all the info to at least pencil out an estimate rather than saying "Is it worth it? Probably, but that is little consolation for those hurt and killed in these crashes." That is a lame argument. This is supposedly an economics blog.

Eric M. Jones

It's just a little luminaire engineering problem. I am sure they already have begun making changes to prevent this from happening.

Mehul Sheth

As well espoused in SuperFreakonomics the simplest answers are usually the best. In this case if we rethink our traffic light fixture I'm sure we could come up with a design that would prevent snow/ice buildup. I'm no engineer, but I would think angling the light fixture downward would help allow snow to slide off easier, minimizing buildup. Maybe IV can come up with something even more simple and cheap!


yeah, 100 years from now people are gonna giggle at this problem- automated transportation systems made this obsolete- brought a new wrinkle to the problem of crashing, however


LEDs are also an issue at airports. They don't give off heat and thus many FLIR heads up display systems used to aid pilots in low-visibility aren't able to pick up new LED runway lights through the fog because they don't create an IR signature for the systems to pick up.

Steven Bone

Your advice 'motorists should know to exercise caution and treat them as if they are stop signs' is the same one that should be followed when the lights are out, but is simply not enough for this situation.

Bear in mind that unlike when the lights are out in ALL directions, snow obscured lights are usually only a problem in ONE direction, thus the obscured person is treating the intersection as a stop sign and other drivers think the intersection is operating normally and are obeying their signals. If it is your direction that is obscured, do not assume that traffic that is stopped will stay stopped or that traffic that is moving toward the intersection will stop. Treat the intersection as if you are the frog in a real-life version of Frogger.


This doesn't sound like a problem without a solution. I don't understand why an additional heat coil is such a problem in terms of energy. It would not be difficult to tie this to a temperature sensor, or even better a sensor that detects how much light gets in and out of the fixture, so that the extra energy use is minimal and LED's would still save energy/money.


I'd like to know the stats on how many lives are saved because the LED's don't burn out.
If the LED is covered in snow wouldn't the proper thing be to treat it as a stop sign? This seems like kind of a non-issue because we already have guidelines for what to do if a signal is out.


It's amazing how fast we forget the past. A simple solution to a reoccurring problem. In the late 50's, heating elements were poured into sidewalks outside entrances of large department stores to help melt ice and snow. A simple application of a heating element which is triggered by two factors of temperature combined with an optical sensor. The sensor sends an infrared light via a LED across the opening if it is diffused it turns on the first triggering, the next is by the temperature. When the snow builds up, on goes the heating elements. Clear ice is not a factor as it still allows the light to be seen. A 1950's solution to a 2010 problem. 60 years in teh making.

Noam Katz

The article states: "Heating up the LEDs would help defeat the purpose of saving energy."

First, it would not defeat the purpose of saving money by having less need to replace burnt-out bulbs.

Second, could not the LED heaters be hooked up to thermostats or switches? During summers, no energy would be wasted on heat. During winters, the heaters could run constantly, or only when it was a cold day, or only when it was snowing, or some other such variation. The technical equipment needed for each variation I just mentioned would probably vary in design and cost, but I have to imagine that at least some of those solutions would be reasonably easy to implement and cost effective overall.


Would electric-powered cars have problems in very cold weather? I know gasoline has a low freezing point which allows cars to keep running. Do currents run significantly slower in low temperatures?

P.S. I don't drive so forgive any ignorance.


Just seems like more of the same to me. You do realize that traffic lights can go out for other reasons and in many types of weather.

If they would just go back to having a cop at every intersection, this could be solved I tell you!

Really, isn't it more the fault of the drivers not paying attention to the road?


Make the green lights LEDs, but keep the red and yellow as the regular hot ones. It doesn't matter much if you can't see a green light.

You only save maybe 40% as much, but the change isn't instantaneous anyway. By the time you've changed all the green lights to LEDs, a technical solution might be available for the others.


IMHO, any analysis of accidents caused by snowed-up LED lights would be useless without a comparison to the number of accidents caused by burned-out incandescent bulbs.

Also, as for the energy penalty of having a heater on the light...it could be designed to only come on when needed. You could have a sensor that would detect the decreased light output and switch on the heat, or at least notify the DPW to come and clean the light. It would probably not add that much to the cost of the light, especially compared to the cost of a large array of high-efficiency LED emitters.

Mr D

Wow, the manufacturer and the customer(government) forgot to do the proper engineering. Having been an engineer on a Satellite earth station network in Alaska I can safely say that the heaters were built in to the antennas and feedhorns. They only run under the right combination of moisture and temperature. This is some of the worst places in the world for rime ice and snow. Building a little heater- sensor in to a streetlight would be a piece of cake and it would only run 1% of the time annually. This is not economics. This is common sense.

Vincent Clement

This is a 'humans not following the rules' problem. If you can't see the traffic light or it is not functioning, you are supposed to treat the intersection as an all-way stop.


One of the best punny titles ever on this blog.


Heating/snow removal tech has been around in security cameras for quite a while now, it should be easy enough to modify it and put it in traffic lights.