Do any readers share concerns that today’s lane-striping reflective materials are less effective than in the past? Seems to me, especially in wet, nighttime conditions, that lane-striping reflectivity is terrible and that headlights don’t seem to be able to pick it up as far down the road as in the past.
— Dan Karbler, Aberdeen Proving Ground, Md.
The first thing Answer Man did was call Ron Gibbons at Virginia Tech. Ron is a lighting engineer and director of the Virginia Tech Transportation Institute’s Center for Infrastructure-Based Safety Systems.
Ron, are today’s lane stripes harder to see?
“That’s always a tricky question, because people forget that their eye changes,” he said. “It’s one of those things, like I can’t remember a snowfall that was up to my knees except when I was a kid. Well, my knees are a lot higher than they used to be.”
Have stripes changed, or have we? Well, we undoubtedly have. Nearly 1 in 5 U.S. drivers is 65 or older. It’s among the fastest-growing driver demographics. Given that most traffic fatalities occur at night, it’s especially important drivers can see where they’re going.
When illuminated by headlights, pavement stripes — yellow for the centerline, white for the travel lanes and shoulders — should seem to glow. They are equipped with what are known as retroreflective materials. When light hits them, the beam doesn’t scatter but is thrown back in the direction of the light source, i.e., your vehicle.
This is accomplished in one of two ways.
A retroreflective device can be glued on top of or embedded in the roadway at regular intervals. We might call it a cat’s eye, but the technical term is “raised pavement marker,” or RPM. RPMs can be quite bright, but they have two drawbacks: They are expensive, and they are at risk of being scraped off the pavement by a snowplow. That’s why cat’s eyes are more likely to be used in the American South than in places with more snow.
Much more common is special retroreflective paint. Actually, it’s not the paint that’s retroreflective but the thousands of little glass beads that are dropped into the still-wet paint — or into hot and sticky thermoplastic — just after it’s applied. (How little? The beads range from 0.0024 to 0.034 inches in diameter.) The top 40 percent of each bead sticks up from the paint, casting light back at vehicles.
Retroreflective stripes are measured in units called millicandelas. There currently is no federal minimum standard for how bright pavement markings must be. But in 2009, the Federal Highway Administration released retroreflectivity guidelines for road signs, and that prompted efforts to come up with something similar for road stripes. Rules are expected to be announced within the next few months.
Our roads would be more visible at night if they were all illuminated by overhead lights. But imagine the expense — and the light pollution. So we do the best we can.
Retroreflective glass beads aren’t as effective when awash in rainwater or when obscured by the grit left behind by sand trucks. And road stripes are eventually eroded by the elements and traffic, the tiny glass beads pounded to oblivion by all those Goodyears and Firestones.
Steve Norkus of Professional Pavement Products, a company that sells striping tools, said that during the recession, many state highway departments cut back on replacing faint pavement markings. Steve said U.S. lane-marking materials are brighter than they’ve ever been. “What people are complaining about is the infrastructure not being maintained,” he said.
If, as promised, driverless cars take over, our roads may need to change.
“Pavement markings have all been designed right now to deal with the human eye,” said Virginia Tech’s Ron Gibbons. Cars bristling with cameras and sensors may require different pavement markings, and highway departments will have “to make sure we’re building an environment to handle all the automated vehicles.”
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