# What are those little yellow A-frame things along the roadside? **URL:** \ **Category:** Factual Questions\ **Created:** [August 22, 2005, 1:17am UTC](https://boards.straightdope.com/t/what-are-those-little-yellow-a-frame-things-along-the-roadside/318051 "2005-08-22T01:17:35Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![jebert](https://avatars.discourse-cdn.com/v4/letter/j/ec9cab/32.png) [@jebert](https://boards.straightdope.com/u/jebert)\ **Post date:** [August 22, 2005, 1:17am UTC](https://boards.straightdope.com/t/what-are-those-little-yellow-a-frame-things-along-the-roadside/318051/1 "2005-08-22T01:17:35Z")
I often see these little yellow signs that look like an A-frame along the roadside in rural areas. Actually they are about the size of and look like the roof of a birdhouse. They are yellow in color with numbers in black on both sides of the “roof”. They are usually mounted on a pipe a bit higher than a fencepost. At first I assumed the sides of the sign were tilted from the vertical to facilitate reading from an airplane, but the numbers aren’t that big - it would have to be a pretty low flyer to read the things. So what are they and why the odd shape? ---
**Author:** ![rackensack](https://avatars.discourse-cdn.com/v4/letter/r/e5b9ba/32.png) [@rackensack](https://boards.straightdope.com/u/rackensack)\ **Post date:** [August 22, 2005, 4:12am UTC](https://boards.straightdope.com/t/what-are-those-little-yellow-a-frame-things-along-the-roadside/318051/2 "2005-08-22T04:12:35Z")
[Pipeline markers?](http://www.pipeline101.com/PipelinesYou/id.html) I realize that one’s orange, but the idea’s the same. ---
**Author:** ![rackensack](https://avatars.discourse-cdn.com/v4/letter/r/e5b9ba/32.png) [@rackensack](https://boards.straightdope.com/u/rackensack)\ **Post date:** [August 22, 2005, 4:21am UTC](https://boards.straightdope.com/t/what-are-those-little-yellow-a-frame-things-along-the-roadside/318051/3 "2005-08-22T04:21:33Z")
[http://www.farwestcorrosion.com/images/fwst4/cars20.jpg](http://www.farwestcorrosion.com/images/fwst4/cars20.jpg) Look for “Aerial Patrol Marker” on [this page](http://www.farwestcorrosion.com/fwst/teststn/cars02.htm). ---
**Author:** ![jdatk99](https://avatars.discourse-cdn.com/v4/letter/j/f08c70/32.png) [@jdatk99](https://boards.straightdope.com/u/jdatk99)\ **Post date:** [August 22, 2005, 4:22am UTC](https://boards.straightdope.com/t/what-are-those-little-yellow-a-frame-things-along-the-roadside/318051/4 "2005-08-22T04:22:03Z")
they are pheremone-baited insect traps that entemologists use to catch specific bugs of interest ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [August 22, 2005, 9:44am UTC](https://boards.straightdope.com/t/what-are-those-little-yellow-a-frame-things-along-the-roadside/318051/5 "2005-08-22T09:44:48Z")
> [@jebert](#): > > At first I assumed the sides of the sign were tilted from the vertical to facilitate reading from an airplane, but the numbers aren’t that big - it would have to be a pretty low flyer to read the things. > > So what are they and why the odd shape? They are, indeed, markers intended to be read by aircraft as well as ground personnel. And yes, pipeline patrol craft _do_ fly quite low. Around here they seem to use helicopters more than airplanes, but I’m sure that varies from place to place. ---
**Author:** ![jebert](https://avatars.discourse-cdn.com/v4/letter/j/ec9cab/32.png) [@jebert](https://boards.straightdope.com/u/jebert)\ **Post date:** [August 22, 2005, 5:19pm UTC](https://boards.straightdope.com/t/what-are-those-little-yellow-a-frame-things-along-the-roadside/318051/6 "2005-08-22T17:19:13Z")
That’s exactly what I see on the roadsides. Wow, I’d think you’d have to be flying at 200 ft or less to see the digits on those things. Watch those wires, boys. ---
**Author:** ![Broomstick](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/broomstick/32/246_2.png) [@Broomstick](https://boards.straightdope.com/u/Broomstick)\ **Post date:** [August 23, 2005, 10:54am UTC](https://boards.straightdope.com/t/what-are-those-little-yellow-a-frame-things-along-the-roadside/318051/7 "2005-08-23T10:54:05Z")
There _is_ a requirement to have 20/20 vision for a commercial pilot’s license (either natural or corrected to that figure). Now you know one of the reasons why. 😉