|LED advantages outweigh potential snow hazards in traffic signals|
|07 Jan 2010|
|Transportation departments can mitigate the potential of snow blocking drivers’ view using simple air scoops on traffic signal tunnel visors |
With the first major snowy blast of winter gripping much of the mid-west and northeast regions of the United States, major news outlets have been reporting on a potentially deadly flaw of LED-based traffic signals. Because the LEDs used in such signals don’t radiate heat, the bulbs don’t melt snow that can accumulate in the sun visor that surrounds each signal light. Traditional incandescent bulbs would melt such snow. Presumably, a snow-covered red light was a key factor in a fatal auto accident near Chicago last April.
But the snowy LED issue is not a new problem. The Colorado Department of Transportation realized the potential danger five years ago, and sought a solution. Such transportation departments are reluctant to give up the cost savings associated with LED traffic lights, and a simple Snow Scoop from McCain Inc (see below) can inexpensively mitigate the problem.
The story of the fatal accident has appeared in a number of places including this Chicago Tribune account. Apparently a driver in a pickup truck couldn’t see a red light and collided with a car making a left turn in an intersection. The collision killed the women driving the car.
LEDs offer significant savings to transportation departments. According to this Chicago Tribune column, a 69W incandescent bulb is replaced by an LED version that dissipates only 11W – an 84% savings. Early on, LED signal heads cost two or three times more that the traditional incandescent heads. Today the premium is in the 60 to 80% range. But the LED signal heads last ten times longer so the savings are substantial when you add up energy cost, the cost of the signal heads, and the labor required replacing failed signal heads.
According to this story from the Des Moines Register, the city saves about $100,000 per year on electricity powering 4,000 LED-based signals. Clearly, the city would like to stick with LEDs and preserve that savings. The motivation has been sufficiently strong that transportation workers in Iowa have manually tapped signals to release trapped snow when conditions were problematic.
Colorado, meanwhile has satisfactorily deployed the aforementioned Snow Scoop Tunnel Visor. McCain VP of Manufacturing Greg Johnson describes the visor "like an air scoop on a hot rod." According to Johnson, the Snow Scoop design utilizes the same force – wind – that causes the problem in the first place. It's wind that blows snow into the visor. Johnson stated, "With snow there is usually wind and we figured that we could use a louver to allow the wind to clear the snow from the visor." The scoop in the design extends upward at an angle from the cylindrical visor and drives wind through a louver slot underneath the scoop on the top of the visor. The cylindrical visor also has a lengthwise slot at the bottom of the design that allows the snow to fall out.
It turns out that the new visor offers a very economical solution to the problem. The Snow Scoop can be added to most existing traffic signals and cost around $20. The image at left shows the air scoop and the louver slot through whic wind enters the visor, as well as the slot at the bottom where snow exits.
|Name: no1anyoneknows Posted: Sun, 10 Jan 2010 17:01|
|"a driver in a pickup truck couldn’t see a red light"
Anyone approaching an intersection needs to ensure that they _positively_ see the signal, and should, at least, slow until they are sure of the signal color, or that it is otherwise safe to proceed.|
|Name: 08xfire Posted: Mon, 11 Jan 2010 18:01|
|Agreed. If he did not see the traffic light as red then what if any color did he see that assures him he had the right of way??!! |
|Name: skeptic Posted: Tue, 12 Jan 2010 02:01|
|Unlike lamp failures, when snow blocks the lights it tends to block all of the lights facing a particular direction at an intersection.
At night or in daylight with blowing-snow conditions, it is quite conceivable that drivers will have no idea that it is a signalised intersection.|
|Name: practickle Posted: Tue, 12 Jan 2010 21:01|
|The slot as a wind louver seems a great idea, until the Sun comes out.
Signals facing East or West will exhibit "sun-phantom" when the Sun's angle matches up with the louver slot. Reducing sun phantom is the purpose of the visor in the first place.
Just use caution with the application.|
|Name: trafficbuster Posted: Wed, 13 Jan 2010 20:01|
|Another potential solution would be to start making more European-style traffic circles instead of 4-way intersections. This would allow many traffic lights to be eliminated altogether. |
|Name: apollo Posted: Thu, 14 Jan 2010 05:01|
|If the three signal lights are arranged horizontally, there would be no snow piling up.|
|Name: profquatermass Posted: Thu, 14 Jan 2010 10:01|
|In Europe we often see busy traffic circles with traffic lights as well. Once a circle gets popular you need to install traffic lights or the route with the most traffic effectively blocks the other roads leading onto it.|
|Name: 45 degrees Posted: Thu, 14 Jan 2010 16:01|
|Here is a sugession: remove the scoops and add a piece of plexiglass at 45 degrees from the bottom of each light to the top of the visor. Then cut off the rest of the visor (on the sides) that sticks out past the plexiglass. It would have to be pretty sticky snow to stick the bottom of a 45 degrees surface. I have heard of a type of plastic that is resistant to sticky snow, but I can't think of the name.|
|Name: sslpro Posted: Fri, 15 Jan 2010 05:01|
|Another solution not mentioned is faceted lens covers using plastics with formed protrusions to mitigate these rare scenerios. The realities are part of the potential purchasers responsibilities, there are multiple solutions - its up to engineers and mfgs to produce an array of skins /housings that are as functional / practical as the base components -the Leds rarely fail early circa 2010.|
|Name: scott mackinnon Posted: Tue, 23 Feb 2010 21:02|
|The shades on traffic lights that cause snow build up are designed to allow drivers to see the light on a bright sunny day and to prevent drivers travelling in other directions to see it. Given that LEDs are much brighter and more focused, removing the shield and making the face flat would prevent snow build up.|