White is best color for self-driving vehicles

Dark hues and metallics are less detectable by lidar systems

Henry Ford famously said a customer can have a car in “any color that he wants, as long as it is black.”

But black on self-driving cars could be deadly.

That can help explain why the

May Mobility self-driving shuttles in downtown Detroit have a white base and why paint companies and carmakers have been working diligently over the past four to five years to get the color spectrum just right for future vehicles.

“Highly reflective colors like white are more detectable by lidar systems,” said Nancy Lockhart, color marketing manager at Axalta Coating Systems in Michigan’s Clinton Township. “Black will be the least reflective.”

The Light Detection and Ranging (lidar) remote sensors that use light to measure ranges in distance won’t be able to “see” dark-colored cars or less-reflective paint colors as well as the more reflective, lighter colors, experts say. That could be a significant problem — leading to crashes — when the roads are shared with autonomous vehicles one day.

“All the colors on vehicles today or road signs, road markings, are all designed for our eyes,” said David Bem, vice president of science and technology and chief technology officer for PPG in Pittsburgh.

Human eyes can adjust, thereby absorbing various light across color spectrums, Bem said. PPG has studied the aerospace industry for years to learn how sensor technology reacts to various colors and reflection. Bem said as the car industry goes to “sensor technologies or anything working off a wavelength,” the visibility spectrum across light to dark colors can impact how those sensors detect and react.

“Dark colors tend to absorb” light, making it hard for sensors to see, Bem said. But “those that reflect well have the opposite effect and can, in extreme cases, blind sensors,” he said.

Axalta and PPG scientists are developing and testing a full range of colors that will be visible to lidar systems in a variety of weather conditions and lighting.

The popular metallic colors such as silver create a challenge, because “if you walk around a highly metallic vehicle, the color changes in different light,” Lockhart said. “So those colors tend to be more complex in determining how reflective they will be on the road because you have AVS coming at it at all angles.”

But the AV industry is so new that the lack of rules and methods for testing AV paint makes the progress for developing it slow going, Lockhart said. Axalta has devised its own test methods and devices to monitor how the various colors it tests will perform in different environments, she said.

“We’re working as aggressively as the industry will let us, but right now there is no pass or fail,” Axalta’s Lockhart said. “There are no regulations as to testing the AV detection systems, so we are looking at how do we best detect things. There is no worldwide testing unit or spec that says this is what you have to test.”

Axalta develops colors in Mount Clemens, Michigan, and then sends them to a new technology center it built near Philadelphia for testing on the vehicles and in environments, Lockhart said.

PPG has developed a coating that allows automakers to better manage the reflectivity of specific light wavelengths, Bem said. Within two years, PPG will bring to market advanced coatings that will absorb less infrared light, but still provide beautiful color, he said.

PPG has also developed a “portfolio of composite coatings” to make it difficult for dirt, water, bugs and road debris to block sensor lenses.

Besides the obvious safety advantage of having the right paint color detectable by AV sensors, there might be a financial advantage too. Lockhart suggests that insurers might offer a discounted rate to drivers with cars that have a higher-reflective paint.

Lockhard is confident of one thing: The world will not return to the days of Henry Ford’s monochrome car fleet.

“I don’t think we’ll get to a world that is so vanilla that we can’t have different colors,” Lockhart said. “The industry will find a way to get there.”