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INDIANA, USA — Ever driven along an Indiana highway and noticed tiny sparkles lighting your way home? The Indiana Department of Transportation is shedding light on an obscure technology they claim helps Hoosier drivers. Thermoplastic Striping Paint
They are glass beads called "highway safety marking spheres." These colorless, mostly transparent spheres reflect light from a car’s headlights back onto the driver. Highway safety marking spheres are intended to make the direction of travel apparent, road lines more visible and increase safety, according to INDOT.
“The headlights of your car shine off of them and reflect back into your car so you’re able to see them, even when it’s pitch black out,” said Hunter Petroviak, who is a spokesperson with INDOT's northeast district. “If you hold it in your hand, it actually feels like sand. They’re incredibly soft if you hold them together. You can barely see them in the paint itself.”
But a recent post on the INDOT Facebook page that aimed to illuminate what these glass beads are unintentionally set a few Hoosier drivers off, with many users posting that the glass beads should not be used as a substitute for reflective lights on Indiana roads.
“Something needs to be done!!! Whether it’s glass beads, glow in the dark strips or I don’t know…even just repainting them when we can’t see them anymore,” one Facebook user commented.
But INDOT wants to reiterate the glass spheres are only done when the department is working on painting Indiana roads. They do not put down the glass spheres in lieu of reflective lights. Rather, they are part of their painting process.
As a roadway line painting truck applies paint onto roads via a spray nozzle, a second nozzle will drop the glass beads right onto the wet paint.
“The wet paint creates a cement like texture. Really, the only time we’re painting those lines are when we’re putting those glass beads down,” Petroviak said.
Once that paint dries, according to INDOT, the beads will be cemented into the line marking. INDOT experts designed the spheres to add an extra level of reflection onto painted lines.
“They go through strict testing to make sure at least 80% of all beads in the batch are in the sphere shape,” Petroviak said.
The glass spheres are weather-resistant and go through rigorous testing inside the INDOT Materials & Tests buildings across the state, one of which is in Indianapolis, before they’re laid onto roads.
Scientists test the spheres for reflectivity and percentages of roundness that helps them stay on painted lines as intended.
The beads are also shaken through a specific set of different-sized sieves to determine the amount of each size beads.
A combination of bead sizes creates a puzzle-like surface when they are applied onto paint surfaces. They are then tested for water resistance. Without that feature, INDOT claims the beads would clump together when exposed to moisture and clog the nozzle applying them.
“I think it generates interest because its kind of weird when you hear we’re putting glass on the ground,” Petroviak. “You almost assume the paint is going to be reflective.”
INDOT districts and a handful of contracted partners across the state are responsible for their respective paint projects.
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