The Visibility Research Laboratory features a 125-foot-long dark tunnel, which is used to test materials for traffic signs and pavement markings. The facility also has capabilities to measure vehicle headlamps, sign lighting and roadway lighting.

When you drive at night and your headlights illuminate a lane marking, it makes you feel safer, right? After all, bright pavement markings are designed to help you stay in your lane and prevent you from running off the roadway.

Called retroreflectivity, special materials in edge lines and lane lines create the brightness. With age and wear that brightness deteriorates. Although we assume there’s a correlation between pavement marking retroreflectivity and safety, up until now researchers have not been able to prove it.

“It’s a hard thing to measure,” says Paul Carlson, Texas A&M Transportation Institute (TTI) Research Engineer, who is also the head of the Institute’s Operations and Design Division. Carlson is known for his pavement marking research and leads TTI’s unique Visibility Research Laboratory. “For one thing, in order to gather good information about safety you would have to know the level of brightness, or retroreflectivity, a pavement marking had at the time someone ran off the roadway.”

As it turns out, Carlson had a near perfect opportunity to conduct a study, thanks to the Michigan Department of Transportation (MDOT).

For years, MDOT has measured the brightness of its pavement markings on individual roadways. Carlson realized that he could compare those brightness levels with the crashes occurring on those roadways.

“Michigan DOT is very serious about keeping its pavement markings maintained. If measurements show pavement markings were dull, they would be replaced. Comparing both dull and bright pavement markings with crash information, we were in a good position to determine if those retroreflectivity characteristics played a role in safety.”

So, Carlson’s study, An Investigation of Longitudinal Pavement Marking Retroreflectivity and Safety, got underway. Sponsored by the Federal Highway Administration (FHWA), he gathered crash data and retroreflectivity measurements from 2002 through 2008. He compared the measurements with certain types of crashes: single vehicle, nighttime crashes that occurred during dry conditions and non-snow time months.

After a lengthy and tedious process, Carlson completed the research in July 2012. He determined that fewer crashes occurred when pavement markers were brighter and newer.

“The evidence is pretty compelling,” Carlson says of the research. “It demonstrates that maintenance of pavement markings retroreflectivity can have a positive effect on safety. I’m confident of the results — brighter pavement markings mean safer roadways.”

In the meantime, Carlson has been working with FHWA as it comes up with a retroreflectivity standard, which would help DOTs across the country know when pavement markings should be replaced.

Read the article

Lines, signs and symbols painted on the pavement play a major role in providing drivers with needed information about how to navigate the roadway safely and legally. In order to ensure that drivers can see the markings at night, the paint is mixed with micro-sized glass spheres, making it retroreflect the light from vehicle headlamps to drivers’ eyes. But as this paint–glass bead mixture is applied to the road, degrades over time, and is reapplied, what effect does it have on the people handling it and on our environment? Researchers with the Texas Transportation Institute (TTI) and the Texas A&M University Zachry Department of Civil Engineering (CE) recently began an effort to find an answer to this question.

Mixed with paint, microscopic glass beads like those seen here help enhance the retroreflective property of pavement markings.

The microscopic glass beads added to pavement paint most often start out as recycled glass feedstock, which can have high levels of arsenic and other heavy metals.

“In the past, arsenic had been used to purify glass. While we no longer purify glass this way, arsenic is still present in recycled glass that becomes the beads,” says Bryan Boulanger, assistant professor in CE. “Volume-wise, a lot of glass beads go down on the roads, and they are constantly being replaced.”

“I estimate that there are about 80 million pounds of glass beads used each year on U.S. highways,” says Paul Carlson, head of TTI’s Operations and Design Division. With such a large quantity in use, private producers and public officials began to wonder if the beads could leach heavy metals into the ground or affect human health.

So the Federal Highway Administration (FHWA) tasked Boulanger and Carlson to find out the concentrations of heavy metals in the beads. After collecting samples from around the country and participating vendors, the beads were ground down to measure the metal contents and determine what chemical forms could leach out. Researchers also observed how the glass beads are handled in the workplace to see what risks there might be to the workers. Since the glass beads are approximately the size of small ball bearings, workers could inadvertently consume them through unwashed hands.

The statistics gathered were incorporated into a risk assessment model that will be used by decision makers at all levels of transportation. The model is currently being reviewed for impartiality and refined for accuracy. An analysis of small samples of glass beads shows only a weak relationship between the metal contents and the retroreflectivity level.

“Glass beads are a very integral part of highway safety. So when considering the risk associated with heavy-metal contents in the beads, decision makers have to balance that with the risk of not having the beads in the paint,” says Boulanger. More research is needed to determine the full impact on pavement marking retroreflectivity, if any, as well as to assess how removing metals from the glass beads will affect their efficacy.

This Issue

Making the Grade: Tomorrow’s Transportation System

Volume 48, Number 1
March 2012
Issue Overview

On this page:

• For More Information

“Glass beads are a very integral part of highway safety. So when considering the risk associated with heavy-metal contents in the beads, decision makers have to balance that with the risk of not having the beads in the paint.”
Bryan Boulanger,
assistant professor in Texas A&M University’s Department of Civil Engineering

For more information:

Bryan Boulanger
(979) 845-9782
bboulanger@tamu.edu

]]> http://tti.tamu.edu/2012/03/01/looking-into-the-retroreflective-glass/feed/ 0 http://tti.tamu.edu/2010/06/01/spotlight-the-visibility-research-laboratory/ http://tti.tamu.edu/2010/06/01/spotlight-the-visibility-research-laboratory/#comments Tue, 01 Jun 2010 15:39:23 +0000 Chris Sasser http://tti.tamu.edu/?p=1317

The Visibility Research Laboratory features a 125-foot-long corridor, which is used to test materials for traffic signs and pavement markings. The facility also has capabilities to measure vehicle headlamps, sign lighting and roadway lighting.

“A dark and stormy night” is more than a clichéd way to introduce a story — it’s a dangerous driving scenario when the visibility of road signs becomes critical for safe passage.

Nighttime traffic fatality rates are three times higher than their daytime equivalents. While fatigue and alcohol play important roles in nighttime crashes, Texas Transportation Institute (TTI) researchers Paul Carlson and Jeff Miles focus on optimizing visibility to help reduce crashes at night.

For over a decade, TTI has developed innovative ways to improve visibility in nighttime driving and played a major role in standardizing visibility test methods. That dedication to finding solutions has paid off with the grand opening of TTI‘s Visibility Research Laboratory, located on the first floor of TTI‘s new State Headquarters and Research Building.

“TTI has a long history of nighttime visibility research with field equipment and human factors studies, but this lab provides a whole new way to conduct and develop standardized testing,” says Carlson, head of TTI‘s Operations and Design Division. “We now have better control of the variables so we can develop new test methods and standards.”

The lab is the first of its kind in a university setting. Previously, researchers stayed up most of the night to conduct visibility studies at the Texas A&M University Riverside Campus while relying on Texas weather to cooperate. Now, with the 125-foot tunnel-shaped facility, those same researchers can run night simulations under controlled conditions at any time during the day. An adjacent conference room provides space for presentations, where sponsors and visitors can examine samples of reflective materials with microscopes.

The lab features a custom goniometer — an instrument with a light source on one end and a frame that adjusts along three different axes on the other. The frame supports the material being tested, such as a stop sign. When the angle changes, a computer records the changing optical data as the light retroreflects off the sign. Researchers can test the retroreflectivity of materials for traffic signs and pavement markings, as well as measure the visibility properties of all types of vehicle headlamps, sign lighting and roadway lighting.

“The benefit of this system and this lab is being able to test 1,001 different samples in a short amount of time to narrow down to a few that we’ll then take out into the field,” says Miles, an assistant research engineer for the Signs and Markings Program. “The goniometer makes testing different geometries quick, accurate and effective.”

One current project uses pavement stripes to test retroreflective optics for night driving to develop new testing methods for state department of transportations that will lead to more consistent quality on the road. In conjunction with new nationwide standards of minimum retroreflectivity maintenance levels for traffic signs, researchers are also using the lab to produce step-by-step guidelines to construct calibration signs near the minimum maintenance levels for nighttime inspections, which will help transportation agencies cost-effectively stay in compliance with the new national standards. Another project starting soon will test how light-emitting diode (LED) technologies could be used in traffic signs in the United States. LED lights are prominently used in signs in other countries, but more research on how to best incorporate LED lighting into traffic signs is needed before they can be adopted by the United States.

“This lab expands our technical capabilities and has the potential to bring in new research partners, including the development of specifications and test methods for other countries and designing and testing experimental materials with private industry,” says Carlson. “It will open the door to expand and diversify our research.”

The research possibilities are numerous since other TTI divisions and Texas A&M University departments can also access the lab. Talks are underway about a possible master’s-level class for the Civil Engineering Department. Human factors studies are being planned for the summer. Also in the future, field instruments could be calibrated in the controlled conditions. The lab currently has the ability to be used for evaluating existing rain measurement test methods but could be modified to study the impacts of fog and rain under a large range of nighttime conditions.

“When drivers travel at night, they rely heavily on the visibility of traffic control devices to reach their destination safely. TTI‘s new Visibility Research Lab is a first-class facility that can be used to help answer technical questions related to the nighttime visibility needs of drivers,” says Greg Schertz, retroreflectivity team leader for the Federal Highway Administration. “Ultimately, we hope that leads to solutions for the huge disparity in the severe crash rates of nighttime versus daytime.”

Retroreflection 101

• “Retroreflectivity” describes how a surface reflects light directed back toward the source.
• “Luminance” means the brightness of a sign. Too much luminance produces the “blooming effect” — when the contrast between the darkness around the sign and light retroreflecting from a sign blurs the letters together, making it hard to read.
• Pavement paints (the stripes on the road) contain micro-sized glass spheres that help drivers see where they are going. The glass beads — so small that a jar full of them looks like powder — retroreflect the light from headlamps to the driver’s eyes. But when the glass beads get wet, their ability to retroreflect light is severely diminished, if not completely lost.
• Retroreflective raised pavement markers (RRPMs) — the roadway bumps some drivers make sport of avoiding when changing lanes — supplement pavement paints specifically for wet driving conditions. The life span of an RRPM is less than 18 months.

This Issue

TTI’s Research Umbrella: Safer Transportation in the Storm

Volume 46, Number 2
June 2010
Issue Overview

On this page:

• For More Information

“This lab expands our technical capabilities and has the potential to bring in new research partners, including the development of specifications and test methods for other countries and designing and testing experimental materials with private industry. It will open the door to expand and diversify our research.” Paul Carlson, TTI Researcher Engineer

For more information:

Paul Carlson
(979) 847-9272
paul-carlson@tamu.edu

]]> http://tti.tamu.edu/2010/06/01/spotlight-the-visibility-research-laboratory/feed/ 0 http://tti.tamu.edu/2010/06/01/now-marking-the-way-research-project-improves-performance-of-raised-pavement-markers/ http://tti.tamu.edu/2010/06/01/now-marking-the-way-research-project-improves-performance-of-raised-pavement-markers/#comments Tue, 01 Jun 2010 14:38:14 +0000 Chris Sasser http://tti.tamu.edu/?p=1405 The worst of driving conditions calls for the best of roadway markers. And with their reflective properties, retroreflective raised pavement markers (RRPMs) have guided many nervous drivers safely to their destination on rainy nights. That’s why RRPMs‘ durability and performance are of critical importance to the Texas Department of Transportation (TxDOT).

A few years ago, though, TxDOT began to notice an increased number of RRPM failures such as poor retention on pavements, physical damage and loss of retroreflectivity. In some cases, mass failures occurred when an entire section of RRPMs disappeared only weeks after installation. In response to this problem, the Texas Transportation Institute (TTI) began to research the causes of premature RRPM failures.

“All the markers that TxDOT was using met the requirements set by ASTM specifications,” says Yunlong Zhang, TTI assistant research scientist and research supervisor “However, RRPMs‘ performance varied significantly, and the results from existing testing methods also did not correlate with field performance. We were asked to identify or develop new lab testing methods that would help us to more accurately predict marker performance in the field.”

Over a three-year period, researchers conducted multiple tasks that included lab and field tests, as well as surveying TxDOT districts and RRPM manufacturers to gather information on existing test procedures and marker field performance.

“For two years we monitored four test deck locations that were selected based on traffic condition and pavement type,” says Zhang. “For example, one of our test decks was on the 610 Loop in Houston, which is a very high-volume concrete roadway. We also had a test deck on a low-volume road with a flexible pavement surface. The goal was to get a wide range of test data in different scenarios.”

This pavement marker shows several failures on the shell. These failures could be caused by something as simple as a stone wedged in the tire tread of a vehicle.

The research yielded several important findings with respect to RRPM performance and testing methods:

• Performance of RRPM products has a wide range and depends on traffic volume, truck traffic and pavement surface type.
• Retroflectivity degrading is directly related to average daily traffic.
• High truck traffic significantly accelerates marker physical damage.
• Marker retention is directly related to installation quality.
• Current testing methods were inadequate and cannot predict field performance of the markers.

Another important finding was that the results from the developed pendulum impact test (see below) had a sound correlation with that of field performance, giving TxDOT a proven marker quality-control tool.

“RRPM failures are not only a public safety issue, but also expensive when you take into consideration having to close the roads for repairs,” says Zhang. “With the results of this research, we were able to recommend that TxDOT emphasize the quality of RRPM installation since we found it directly relates to performance in the field. And TxDOT is also now able to better predict the life expectancy of these markers for all types of roadways and traffic volumes.”

“The researchers did a great job of modeling the forces on a pavement marker from vehicular impact. This was cutting-edge work,” said Darren Hazlett, with the Construction Division at TxDOT and project director. “They also produced a pendulum impact test that could be used to test markers and have transferred this test equipment to us.”

Pendulum Impact Test

During the project, the team discovered that many of the failures of retroreflective raised pavement markers (RRPMs) began with the fracture of the outside shell. These failures could be caused by something as simple as a stone wedged in the tire tread of a vehicle. Consequently, failure occurred due to the impact of a hard small object with the surface of the RRPM.

“What we needed was a testing procedure that evaluated the ability of the RRPMs to absorb energy-of-impact type loading,” says Yunlong Zhang, research supervisor. “Since there was nothing that existed, we designed and fabricated the pendulum impact test device.”

The pendulum impact device is a nifty piece of equipment that allows users to test the durability of the RRPM outer shell using different weights. The RRPM is clipped into place, and a weighted arm swings down and impacts the marker. Different weights can be added to the end of the pendulum arm to increase the force exerted on the marker at impact. The marker support is adjustable, so four different impact points can be tested to give a full evaluation.

“We tested six RRPMs with this device using all six weight configurations at each of the four impact positions,” says Zhang. “Using this device to test markers before they are installed will give TxDOT a better idea of the durability and performance they can expect, particularly in high-traffic areas.”

For more information:

Yunlong Zhang
(979) 845-9902
yzhang@civil.tamu.edu

Publications:

0-5089-1: “Development of Measures to Improve Field Performance of Retroreflective Raised Pavement Markers”

0-5089-S: “Raised Pavement Marker Improvements”

This Issue

TTI’s Research Umbrella: Safer Transportation in the Storm

Volume 46, Number 2
June 2010
Issue Overview