Have you ever noticed that most traffic signals are oriented such that the red light is on top and the green light is on the bottom? If you haven’t, you might be color-blind, like me. But trust me, red is on top and green is on the bottom (I learned the hard way, “Sorry about that officer!”). And there is a very simple explanation for this – it has to do with something called packaging. Traffic signals are packaged in a very specific manner. The crate containing the traffic signal is prominently stamped, “THIS SIDE UP.” This imprint generally (hopefully) confirms that the red light is on top. And if the signal contractor is astute when unpacking the signal, he will follow the directions on the crate and the red light will, once again, end up on top.
Now, I know what some of you are thinking, “I could be watching cat videos instead of reading this column.” But guess what, I am just now getting to the good part: some traffic signals are oriented horizontally; what’s up with THAT? A sore neck that’s what…
That, my friend, is why we are here. That is why you are expanding your mind while your counterparts are watching cat videos. You are soon to become one of the few people in the world who knows the answer to that question, and just a second while I try to remember the question, oh yeah, sec…
Now there are four reasons for positioning a traffic signal in a horizontal fashion (plus one bonus reason):
Areas of high winds. Traffic signals are more securely supported by the signal structure when attached horizontally (this, by the way, is probably the most common reason).
Consistency. To be consistent with the orientation of nearby traffic signals is a great reason. Traffic engineers do many things for the sake of Consistent Driver Expectations. CDE is always a safety consideration when making traffic engineering decisions.
Vehicle clearance requirements. In order to satisfy minimum legal clearance requirements for certain vehicles, traffic signals must sometimes be situated horizontally.
To be visible. Occasionally, there are bridges or tunnels that inhibit complete visualization of traffic signals unless they are mounted horizontally. When exiting a tunnel or other area of restricted vertical visibility, a horizontal light means that drivers see all three lights at the same time (but all three lights should never be “on” at the same time – this is a horrible idea and was debunked several years ago).
Cool Factor. And sometimes horizontal layouts are simply aesthetically pleasing. As you’ve likely observed, engineers, and traffic engineers in particular, have an uncanny sense of fashion.
And how are traffic signals oriented in countries where they drive on the wrong side of the road? That’s a great question – nobody really knows. Not yet. Not until next week anyway…
Chet Skwarcan has over 25 years of traffic engineering experience and can be reached at Chet@TrafficEngineering.com.