Ironically, the "buttons," as they colloquially known among highway people, are meant to enhance visibility, not impede it. "The markers enhance visibility by reflecting automotive headlights while also providing a tactile warning when drivers cross lanes. The markers, as a result, improve overall road user recognition and motorist safety," says Nevada Department of Transportation Public Information Officer Tony Illia. "They act as reflectors for nighttime driving." Besides, "if you're drifting or asleep at the wheel, you'll feel the bump, so that's the reason why. We found that providing that tactile warning has significantly reduced crashes." A Virginia Department of Transportation study put the crash-reduction rate at 11 percent.
These raised buttons are also known as "Botts' dots," or "turtles," if you happen to live in Washington State or Oregon. Their closest cousin among highway markers are so-called "rumble strips." Botts' dots derive their name from the scientist who headed up the research project that developed them in 1953, Dr. Elbert Dysart Botts. They are commonly made of ceramic or polyester. Highway departments like them because of their durability: It saves the cost and labor of repainting road lines. In some places, dots alternate with reflective, orange Stimsonite markers, to further enhance visibility.
Dr. Botts' dots were invented as a response to a high number of car crashes in post-World War II California. At first they were nailed to the highway, creating a problem that should have been foreseen: When the dots came loose, the nails punctured car tires. The California Department of Transportation (Caltrans) then developed an epoxy that made Botts' dots a low-risk, low-cost proposition. While the preponderance of domestic Botts' dots are on California roads (20 million of them), the "turtles" are also common to Nevada, where three dots alternate with a Stimsonite marker.
Use of "turtles" gradually spread across the South and Southwestern states, although in areas susceptible to snow, regular stripes are the preferred lane marking. That's not due to visibility issues but because snow plows will scoop the dots right off the roadways. The same is true of Stimsonite markers, although metal castings have been developed to safeguard them from the snowplow's maw. Botts' dots have been such a success that they are a common sight on roadways in the Arab nations, as well as in some sub-Saharan countries. So, if you're driving in a desert climate, you can expect to see Botts' dots marking the path of your journey.
