Why Are the Lines on the Roads Yellow?

Just be glad they're not black! (Yes, that was once an option!)

It’s one of the first things you learn in driving school—or maybe you even learn it before driving school, just from observation. On the road, white lines separate vehicles going in the same direction, and yellow lines separate vehicles going in different directions. But how were those specific colors chosen?

If you guessed that it has to do with the color contrast with the dark-colored road, you have the right idea. But it’s not just because of the contrast with the road—it’s because of the visibility of the color yellow in general, according to Kelsey Mays, senior consumer affairs editor of Cars.com. Even from the earliest days of road transportation, “yellow was recognized…as a highly visible color,” Mays told Reader’s Digest. “There are manuals from as early as the 1920s that noted yellow was one of the most visible colors.” Yellow’s visibility is also part of the reason it gets a prominent spot in our tri-colored traffic lights. Find out exactly why those are red, yellow, and green.

The first-ever Manual of Uniform Control Devices for Streets and Highways, published in 1935 in hopes of providing some standardization to road markings, offered three separate options for the colors of lane dividers. Those colors were white, yellow, and, of all things, black. Of those three, different jurisdictions could choose “whichever color had the most contrast with the road,” Mays explains.

Needless to say, that wasn’t often black! The darker color had “fallen out of favor” by the 1940s, Mays says, leaving “a two-horse race” between yellow and white. And for the next 30 or so years, the two colors remained the primary choices, with no specific designation for each. It wasn’t until 1971 when a federally administered re-write of the Manual debuted, that yellow and white were determined to mean different things. According to that manual, yellow would only divide two-way traffic and white would be reserved for traffic going the same way.

As for why which was which? Well, even before 1971, yellow had been emerging as “a predominant color to signal caution,” Mays says. This, of course, was partly because yellow had been part of traffic lights for a long time. Even stop signs used to be yellow, before the development of a reflective red dye that wouldn’t fade. So in 1971, yellow became the color that was to specifically denote the more dangerous divide.

Next, get to the bottom of another travel-related color mystery: Why are airplane seats usually blue?

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Meghan Jones
Meghan Jones is a Staff Writer for RD.com who has been writing since before she could write. She graduated from Marist College with a Bachelor of Arts in English and has been writing for Reader's Digest since 2017. In spring 2017, her creative nonfiction piece "Anticipation" was published in Angles literary magazine. She is a proud Hufflepuff and member of Team Cap.