AUSTIN (KXAN) — As more and more schools in Central Texas begin a new school year, you’ll no doubt be seeing more of those big yellow buses driving around your neighborhood picking up and dropping off students.

But those buses aren’t all yellow, many have their roofs painted white. Why?

According to a 1992 New York Times article ,recently referenced by Accuweather, a school bus roof color can have a big impact on the temperature inside.

A pilot program in North Carolina in the early 1990s tested the theory that a school bus with a white roof would make for a cooler experience for the passengers. The results were profound.

The program found white-topped buses had internal temperatures an average of 10 degrees cooler than yellow topped buses. In the hottest times of the day the difference was as much as 17 degrees cooler. Bus drivers also reported seeing behavioral improvements in the children riding the bus, suggesting the kids were more calm as a result of the temperature drop.

Separately the study found that these two-toned buses were reported to be easier to see by other motorists. This specific study tested orange colored buses as the second tone.

The drawback? Well, school districts at the time had to pay several hundred dollars per bus for a white roof. These school buses were also cooler in the winter, but not by as great of a margin. Average temperature drops in the winter were only 3-4 degrees for white-topped buses compared to the all-yellow type.

North Carolina wasn’t the first state to implement use of white-topped buses — they reportedly first originated in California in the 1970s, roughly 50 years ago!

In Depth: Texas school buses

In the 2016 version of the Department of Public Safety’s document “School Bus Specifications” there is a section stipulating the color of Texas school buses. Section 75 is titled “White roof” and states “The roof of the bus painted white.”