The Reason Why School Buses Are Yellow

The science behind colors is fascinating, and it is the unique way they interact with our eyes and the environment that decides how to best apply them. Take, for example, the traffic lights, or danger signs, which are red in color. It's a deliberate choice because the wavelength of red color is the highest in the color spectrum, and as a result, it scatters the least. Therefore, it is clearly visible, even from a distance or foggy atmosphere. A similar visibility is applied to school buses, which are coated in a signature yellow color.

The specific name of this shade is National School Bus Glossy Yellow. According to the National Transportation Safety Board, roughly half a million buses carry children to schools on a daily basis. They are deemed safer than an average car owing to the stringent safety measures put in place. A part of it can be attributed to their looks, which guarantees them an added dash of cautionary priority on roads. 

Giving them a standardized yellow coat of paint across the country (and in many other regions of the world) helps achieve that effect. The yellow shade, which is also referred to as National School Bus Chrome, has almost become synonymous with schools, in the same vein that red shines on a Ferrari, the jet black shade of hulking government agency cars, or even a rare yellow Boss 302 Laguna Seca. So, how was the color yellow adopted for school buses, and what's the science behind it? Let's break it down.

One would think there is some color mandate for school bus paint color that is enforced by law. Well, that's not the case, as per the National Highway Traffic Safety Administration, which makes it clear that the federal law doesn't enforce a yellow color code for school buses. However, as per the agency's guidelines — specifically number 17, titled Pupil Transportation Safety — there is a recommendation to adopt the special yellow color coat.

"Among other matters, Guideline 17 recommends that school buses be painted "National School Bus Glossy Yellow" and have other uniform identifying characteristics. The uniformity of school bus appearance helps motorists identify the vehicles as school buses," the NHTSA says. There are, however, other federal requirements for vehicles engaged in school transportation. For example, such vehicles should carry at least 11 passengers, and must meet the Federal Motor Vehicle Safety Standards, drafted specifically for school buses.

Other rules include measures such as stop arms, occupant protection gear, and energy-absorbing backs, to name a few. But as far as color codes go, yellow is not mandatory. Local governing bodies have the right to set up their own policies regarding the appearance of school buses so that they can be easily identified. Multiple countries across Asia and Europe also rely on yellow school buses, but not exclusively. In New Zealand, for example, buses can be coated in any shade, but they should be properly marked with identifying signs and text.

The origins of standardizing yellow as the color of school buses go all the way back to 1939. Frank W. Cyr, known as the "father of the yellow school bus," picked up the color with help from peers after conducting his own research into the transportation of school children. A professor at Teachers College, Columbia University, he invited fellow educators, folks involved in the manufacturing of vehicles, and even paint experts to a conference in 1939.

It was at this conference that the first set of standardized safety rules for school transportation vehicles was proposed, in the form of a 42-page booklet. It covered everything from the specification of the axle and battery safety to the color code. Interestingly, the booklet's cover had the same shade that they selected for school buses, as per The New York Times.

At the conference, a total of 50 samples were showcased by Cyr, and eventually, a committee of education officials picked the shade that we now know as the National School Bus Glossy Yellow. "You can't buy a bus that doesn't meet that formula," Bob Riley, executive director of the National Association of State Directors of Pupil Transportation Services, was quoted as saying by the outlet. "We've all been born and raised knowing what that is."

We have now firmly entered the age of electric cars, but even with a fundamental makeover of the vehicle propulsion tech, like Daimler's Jouley electric school bus, or those equipped with satellite internet access, the iconic yellow remains a mainstay.

Buses have been moving students to schools as far back as 1914, but the yellow color code did not become a norm until 1939, as per the NHTSA. But why yellow, and not any other color? There's some cool science behind it. Our eyes contain special light-detecting cells, which are scientifically known as photoreceptors. There are two kinds of photoreceptors — rods and cones — tasked with detecting light signals and converting them into images that our brain can process.

Cones, in particular, are responsible for detecting colors and sit at the center of our visual field to break down minute details of the world around us. There are three types of cone photoreceptors, each specialized for red, blue, and green sensitivity. Just like color mixing on a palette, our brain essentially reads the signal overlap coming from these cells to identify the exact color in front of our eyes. Yellow happens to sit in a lucky wavelength spot.

According to the American Academy of Ophthalmology (AAO), when red and green cones are activated by light, and the combined signals are sent to the visual cortex region of the brain, it processes the signals and deduces that the color we are seeing is yellow. The processing is based on the strength of the signal and how many photoreceptors were activated. In a nutshell, the yellow color is a result of two optical cone signals coming together.

"If you get a pure wavelength of one color...and you hit just one cone with it, you're going to have x amount of transmission of signal to the brain. But if that [wavelength] were to stimulate two cones, you'll get double the amount of transmission to the brain," AAO spokesperson, Ivan Schwab, was quoted as saying by the Smithsonian Magazine. He further suggests when the color yellow was picked at a conference discussing school bus safety measures, they landed at the scientifically apt choice. Was it luck? We are not sure, but as Schwab puts it, "they hit it."

Now, we already know that the visual signals that produce the image of a yellow object in our brain are strong as they come from two separate photoreceptor cells. But there is another aspect that makes yellow a special case. Citing scientific research, the non-profit Children's Museum of Indianapolis mentions that the "lateral peripheral vision for detecting yellows is 1.24 times greater" compared to other colors, such as red. In a nutshell, a yellow bus is hard to ignore across the field of view.

The whole objective behind the strict safety norms put in place for school buses is to avoid conflict with fellow motorists. "Motorists tend to want to get where they are going, with little interruption and as quickly as possible," says the NHTSA. As per the rules, they are supposed to stop as soon as a school bus starts flashing its yellow light as it decelerates and the red lights on a halt. Picking high-visibility colors such as yellow and red, therefore, helps ensure safety for all.