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Blue lights on traffic lights?
October 24, 2005 1:29 AM   Subscribe

Early nineties, blue lights on a traffic light below the standard green one. Am I crazy? What were they for?

This was in Westchester County, NY. (North of NYC.) The blue light was much the same as the other lights but with a blue lens, hanging below the green light. I never saw one lit. They're not around anymore, and they were always sort of rare, but there were several if my memory isn't failing me.

I find on Google two kinds of references to it - both of them seemingly new things since the internet became mainstream. One is for catching people running red lights, one is for emergency vehicles. The former seems to imply that I would have seen the blue light on at some point, and the latter has a white light attached as well.

I definitely remember childhood conversations about the nature of the blue light, but no one knew what it was for.
posted by TheOnlyCoolTim to Travel & Transportation (9 answers total)
 
My all-time favorite page on traffic signals is signalfan.com.This guy has an impressive historical collection along with a good detailed history behind the different signals. I don't see any references to it with a quick look through his page - maybe you can find it?

A blue light has never had any official meaning by the NHTSA as far as I know, so it would most probably be a local and maybe illegal thing. Traffic signals everywhere in the US absolutely must conform to federal government standards and there is nothing about blue lights. As a civil engineer I am pretty familiar with these standards.

Most probably it is a faded green light. Some cheaper lenses have been known to fade from green to blue. Possibly it was on a turn arrow light which would explain the location below the green light. Also without seeing it lit it is generally hard to see what color it is.
posted by JJ86 at 2:39 AM on October 24, 2005


Ask on misc.transport.roads. Them roadgeeks know stuff.
posted by dhartung at 3:34 AM on October 24, 2005


My guess, a receiver for a device to turn red lights in to green for emergency vehicles?
posted by ae4rv at 6:30 AM on October 24, 2005


K-Mart had these installed to let potential shoppers know when there was a blue light special in the K-Mart down the road from these lights, or perhaps not.

Might it be this:

Blue lights spot red light runners
New device 'rats' on violators

Pleasanton has installed small blue lights at several of its most dangerous intersections to help traffic cops spot and then safely pursue red light runners coming from the opposite direction.

A motorcycle patrol officer, sitting curbside on northbound Santa Rita across from Safeway, can monitor motorists making left turns in the southbound lanes onto eastbound Valley Avenue. When the officer sees a blue light turn on, that means the left turn signal has turned red. Any motorist who proceeds across the pedestrian crosswalk at that point is running the red light and can be ticketed.

posted by caddis at 7:21 AM on October 24, 2005


ae4rv: No, most of those receivers are IR or "strobe" variety sensors (in fact, I've never heard of any others). A blue lens doesn't really make sense for either and they typically are mounted in a different position (on the pole) as oppose to where the signal lights are.
posted by phrontist at 7:21 AM on October 24, 2005


My northwestern PA hometown has something like that- it's a bright white/blue light activated by emergency vehicles to warn motorists of it's approach, but it's mounted separately from the traffic light.
posted by puddinghead at 7:42 AM on October 24, 2005


JJ86: is it absolutely true that all traffic signals must conform to the NHTSA standards? How do they get away with the famous green-on-top traffic light on Tipperary Hill in Syracuse, NY (or doesn't the law take light position into account?)
posted by Opposite George at 11:33 AM on October 24, 2005


I'm too lazy to read and interpret, JJ86 and Opposite George, but look here.
posted by Kwantsar at 12:14 PM on October 24, 2005


The MUTCD is the guidelines for the FHWA which is one of the organizations of the USDOT which deals specifically with highways and not all public roadways. Even so, the MUTCD is typically used as a general guideline for the design of all roadways. I was wrong about the NHTSA which only enforces standards regarding motor vehicles instead of the roadways.

Us engineers usually use these guidelines as gospel and design faithfully according to their word. So it usually doesn't happen that things are different than the standards unless there is an extremely good reason. I have never heard about cases like that but assume that if federal guidelines aren't followed then a municipality would forfeit federal monies and grants to build roads. IMO, a municipality could be liable in the case of an accident at an intersection which did not follow standard specifications. Private roadways, OTOH, don't need to necessarily worry about these guidelines and could use the colors of the rainbow on their traffic lights if they wanted.
posted by JJ86 at 1:31 PM on October 24, 2005


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