Those Half Black & White Stripes On The Highway Actually Serve A Clever Purpose

Lane lines that look half white and half black are becoming a common sight for drivers on newer stretches of concrete highway across the country. Called contrast pavement markings, they are designed to solve a common problem with standard white lines. And no, it's not white line fever, also known as highway hypnosis. It's that they wash out on pale pavement, with the white stripes on light concrete almost disappearing on bright days. By giving the eye something darker to focus on, the black component goes a long way in fixing that.

Traffic-safety engineers explain it as creating the same effect you get when a thick white line pops against dark asphalt. The difference is built in here, with alternating white and black strips (known as "lead/lag") or white lines bordered with a thin black outline. Agencies have been expanding their use for two decades, and many now include contrast markings whenever concrete pavement is installed or rebuilt.

While the markings look simple, their impact on safety has turned out to be significant. Even minute improvements in visibility can go a long way, since about half of all fatal roadway crashes across the nation are lane departure crashes. Research in 2022 from the Illinois Center for Transportation and the Illinois Department of Transportation looking at data across six states found that contrast pavement markings reduce total crashes anywhere from 12% to 29%, depending on how many lanes the highway has. Even when looking only at fatal crashes, there were reductions of 7% to 19%.

A 2024 study using Indiana data saw even higher gains: 42% fewer crashes on roads with bordered centerlines and 44% fewer with lead/lag patterns combined with bordered edge lines. These studies controlled for lane width (wide lanes are known to be more dangerous than narrow ones), number of lanes, and roadway design, and removed crashes tied to extreme weather. Even property-damage-only crashes measurably improved.

Nowadays, cars' driver-assistance systems are increasingly reliant on the cameras onboard to stay in the center of their lanes, while making us more distracted as drivers. Since modern lane-keeping systems look for the contrast between light and dark pixels, these markings give the cameras a more visible target to follow. The lines are also laced with glass beads that reflect sunlight or car headlights at drivers, further increasing visibility. These do their job even in the rain, because some of them are slightly taller, sitting slightly above the surface when the road is covered in water.

Agencies are also planning ahead. As connected and automated vehicles become more common, pavement markings will be one of the core pieces of infrastructure those systems depend on. Federal researchers are studying how sensors read different types of markings and how to keep them detectable in rain or low sun. Some agencies are even exploring enhanced markings that use magnetic signatures or radio-frequency identification tags to help vehicles anticipate curves and calculate safe speeds.