Texas

Why is it so hard to see the queues on Austin roads at night?

From KUT:

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North Austin resident Jennifer Tull clutched the steering wheel of her Toyota Corolla while driving for free houseplants in the Copperfield area one night. The lane lines on the pavement seemed to disappear before her.

“There are a lot of places in Austin where the lanes themselves are very, very hard to see at night,” she said on a rainy day in North Austin. “It can be really scary if there’s oncoming traffic, just hoping they’re not trying to play chicken with you. And if they have bright headlights, it’s even worse because you’re just driving into bright lights.”

Tull wondered why the lines were so hard to see in the dark, so we looked into this for our ATXplained project.

More than half of the road deaths in Austin happen overnight. Quite often in accidents, people leave their lane, so the city authorities try to make the lanes look bright.

“We have about 40 technicians and they work hard every day,” says Lauren Seyda, who is in charge of signs and markings for the Austin Transportation Department. “They feel the burden of having a lot of work to do.”

The city aims to repaint half of the city’s main thoroughfares – so-called highways – every year. It’s about 185 miles of streets. In the last fiscal year, Austin repainted 54% of his arteries. Non-trunk roads change lanes every four years or so.

“We could have 100 more employees and all the trucks in the world and still have work. There are just so many streets,” Seyda said.

The marking machine sprays lines and then tiny glass beads, almost like a powder, are sprayed from above and adhere to the paint.

Each glass bead works like a small directional mirror, reflecting the light from your headlights back at you. Directional reflection of light is called retroreflection. This is why freshly painted road markings seem to glow at night.

But when it rains, the reflectivity is destroyed.

“Water, instead of reflecting light back to the source, simply scatters the light through refraction,” says Chandra Bhat, engineer at UT Austin’s Center for Transportation Research. “Essentially, the light doesn’t return to the driver, it just spreads all over the place and it becomes difficult for the driver to see it.”

Lines can also quickly become covered in dirt and other pollutants from cars and trucks. The problem is often exacerbated near construction sites and other places where mud can be more likely to splash along the road.

Eventually, the glass beads just wear off.

“The issue that comes up here is cost,” said Adam Pike, an engineer who studies road markings at the Texas A&M University Transportation Institute. “Like standard waterborne glass bead paint, this is really your primary road marking. This is the cheapest system. As with most things, you get what you pay for.”

The city now spends about $6.6 million a year hiring two sidewalk marking and signing companies.

Other path marking materials include something called thermoplastic, which is used for crosswalks, arrows, and words you see on the street. The city sometimes uses thermoplastic for lane markings, and while it lasts longer, thermoplastic can also get dirty, fade, and crack. If the street needs to be refurbished, Seida says the thermoplastic needs to be sanded down.

Raised road signs, those little reflective squares on the ground, also improve visibility at night, but they can cost a few dollars to install.

“On high-traffic roads, they need to be replaced quite often,” Pike said.

3M makes pavement marking tape called Stamark, which uses high-tech ceramic balls instead of glass. Stamark can last for years but costs 10 times more than paint.

“It will definitely be more expensive considering only the initial purchase price, but this tape can last a long time,” said Deng Chen, vice president of 3M’s Transportation Security Division. “When you look at the cost of this solution over time, it’s basically the same and sometimes even cheaper than putting on a cheap coat of paint that can last anywhere from six months to a year.”

Austin is experimenting with more reflective materials, including some 3M products. A pilot project at several high accident intersections includes the use of 3M thermoplastic paint with ceramic beads to mark crosswalks and lanes. Austin-Travis County ambulance stations have used Stamark for years to help ambulances in hard-to-reach areas.

Ultimately, the federal government may force Austin to use more expensive materials. And there will be millions of dollars of federal funding to help pay the bill.

The US Department of Transportation has for the first time adopted new minimum reflective levels for road markings. State and local agencies have four years to come up with a plan to keep lanes lit at night.

But there is no deadline for replacing faded markings.

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