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.

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/2012/03/01/looking-out-for-pedestrians/ http://tti.tamu.edu/2012/03/01/looking-out-for-pedestrians/#comments Thu, 01 Mar 2012 17:24:47 +0000 Tobey http://tti.tamu.edu/?p=8265 Beacons, Pavement Markings Improve Crosswalk Safety

It can feel like you’re taking your life into your own hands when you cross some of Texas’ wide, high-speed roads. Sometimes the only thing that alerts drivers to a crosswalk is the thin white lines on the pavement. That’s not much to stand between you and a vehicle hurtling toward you.

Researchers at the Texas Transportation Institute (TTI) are trying to make things easier for both you and the driver coming toward you. Two recent research studies on pedestrian crossings have aimed at making crosswalks safer and more efficient. The first study, involving pedestrian hybrid beacons, evaluated crash data before and after installation of the treatment, while the second study examined the visibility of different types of crosswalk pavement markings.

“Both studies are influencing national standards and making conditions better for pedestrians,” says Kay Fitzpatrick, manager of TTI’s Roadway Design Program, who led the studies.

Pedestrian Hybrid Beacon

The HAWK treatment was the forerunner of the pedestrian hybrid beacon, which is helping make crosswalks safer for communities across the country.

In 2009, the pedestrian hybrid beacon was added to the national Manual on Uniform Traffic Control Devices (MUTCD), the Federal Highway Administration (FHWA) document that defines standards for installing and maintaining traffic control devices on public roadways. TTI had an integral role in getting the device recognized for the safety it brings to pedestrian crossings.

The path to getting the safety device included in the manual began in the late 1990s when Dr. Richard Nassi, transportation administrator with the City of Tucson (now retired), developed the predecessor of the pedestrian hybrid beacon, the High-Intensity Activated Crosswalk (HAWK) pedestrian beacon. Today’s pedestrian hybrid beacon, like the HAWK treatment, has more than one cue to alert drivers to the presence of the crosswalk. At the crosswalk, the pedestrian pushes a button and activates the beacon. A flashing yellow light and then a steady yellow light warn drivers that they will need to stop. When the light turns red, the pedestrian can safely cross the street.

The effort to gain widespread use of the pedestrian hybrid beacon culminated in an FHWA study to evaluate the safety effectiveness of the device. TTI performed a before-and-after study to determine how the device actually worked in the field.

“We performed a statistical evaluation of crash data from Tucson, typically three years before installation of the treatment and then three years after installation,” says Fitzpatrick. “We found a 29 percent reduction in total crashes and a 69 percent reduction in pedestrian crashes.”

This dramatic reduction in crashes proved to FHWA how important the pedestrian hybrid beacon can be to pedestrian safety. “Many agencies are afraid to try new devices because of the possibility of increased crashes. TTI’s crash study showed that the pedestrian hybrid beacon reduced not only pedestrian crashes but also total crashes, making agencies more willing to try the device and invest money in it. You can depend on the quality of the work done at TTI,” says Mike Cynecki, retired traffic engineering supervisor with the City of Phoenix.

“We’re helping change national policies to make it safer for pedestrians, and also to make it easier for them to cross at clearly marked crosswalks,” says Fitzpatrick.

Crosswalk Markings

A second TTI study evaluated pavement markings at crosswalks for possible inclusion in the next edition of the MUTCD. Research focused on determining the relative daytime and nighttime visibility of crosswalk marking patterns.

“We looked at the types of markings currently in use at crosswalks and narrowed our focus down to the three most common patterns for investigation,” says Fitzpatrick. “We were very fortunate that Texas A&M University allowed us to place temporary pavement markings around campus as part of this study.”

Volunteer drivers set out in TTI’s instrumented vehicle, drove through campus on a predetermined route, and told the accompanying researcher the moment they first saw the crosswalk pavement markings. The route was driven during daytime and nighttime, and clockwise and counterclockwise, to reduce possible bias.

TTI studied three crosswalk marking treatments: bar pairs (left), continental markings (center) and transverse markings (right). Researchers found that bar pairs and continental markings performed better than transverse markings.

The resulting data allowed the research team to calculate the detection distance for each crosswalk and then determine how each type of treatment performed.

“Bar pairs and continental markings were visible from a longer distance than transverse markings,” says Fitzpatrick. “This is intuitive because they’re wider than transverse markings. What we were interested to see is that bar pairs performed as well as continental markings. Bar pairs use less marking material, and that can save agencies significantly over several crosswalks.”

The research effort was so successful that a paper about it won the D. Grant Mickle Award for the outstanding paper in operations and maintenance at the Transportation Research Board’s 90th Annual Meeting in January. (See the “TTI at TRB” article for more information about this award.)

TTI Bikes!

TTI is kicking off a bike-sharing program on the Texas A&M University campus. The effort is designed to demonstrate and promote the benefits of alternative transportation modes — and hopefully inspire others to get on board.

Shawn Turner (left) is leading the TTI Bikes! effort to encourage employees to use bicycles on campus, rather than motor vehicles.

Participants in the program are required to complete a bicycle safety training course, wear helmets, and obey all traffic control devices and regulations. The TTI program includes four bicycles: two each at the CE/TTI Tower and the State Headquarters and Research Building. Participants can check out a bicycle and then return it within 24 hours.

Employees can use the bicycles for interoffice transport and courier service on campus, rather than using an agency or personal vehicle. Bikers benefit from exercise, an environmentally friendly alternative to driving, and the ability to park closer to buildings (something always welcome on a college campus).

Bike-sharing programs are catching on in many U.S. cities, including Washington, D.C., San Antonio, Austin — and now College Station.

This Issue

Making the Grade: Tomorrow’s Transportation System

Volume 48, Number 1
March 2012
Issue Overview

On this page:

• Pedestrian Hybrid Beacon
• Crosswalk Markings
• TTI Bikes!
• For More Information

“Many agencies are afraid to try new devices because of the possibility of increased crashes. TTI’s crash study showed that the pedestrian hybrid beacon reduced not only pedestrian crashes but also total crashes, making agencies more willing to try the device and invest money in it. You can depend on the quality of the work done at TTI.”
Mike Cynecki,
retired traffic engineering supervisor with the City of Phoenix

For more information:

Kay Fitzpatrick
(979) 845-7321
k-fitzpatrick@tamu.edu

]]> http://tti.tamu.edu/2012/03/01/looking-out-for-pedestrians/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/then-ttis-contributions-to-pavement-marking-started-early/ http://tti.tamu.edu/2010/06/01/then-ttis-contributions-to-pavement-marking-started-early/#comments Tue, 01 Jun 2010 14:46:50 +0000 Chris Sasser http://tti.tamu.edu/?p=1414 The Hot-Melt Plastic Stripe as a Pavement Marking Material

By Charles J. Keese
(Excerpted from Bulletin No. 130, Texas Highway Department, March 1953)

“PAINT IS THE STRIPING MATERIAL FOR THOUSANDS OF MILES OF STREETS AND HIGHWAYS. However, its resistance to wear and weathering is so poor, that frequent maintenance of stripes is necessary. Such maintenance is costly.

Recent experimentation has produced an easily applied plastic road marking material of good durability.

It is rosin-alkyd resin which can be compounded in either white or yellow color and applied to pavement in hot-melt form. Preliminary tests have indicated a service life of several times that of standard paints on both asphalt and concrete pavements.

Highway technologists have expressed such keen interest in the material that specifications are being made available in this publication. Trade names are mentioned only as necessary to identify ingredients.

It is hoped such information shall be useful in providing greater serviceability from our streets and highways while at the same time reducing striping maintenance costs.”

A forerunner of today's automated striping machinery, the hand-powered machine was used for laying the hot-melt plastic paint stripe. It consisted of a tricycle cart, gasoline heating unit, oil-bath kettle, metal screed box (held firmly to the pavement by springs) and a wooden attachment for applying reflectorizing beads.

The thermoplastic pavement striper was invented at the Texas Transportation Institute (TTI) in the early 1950s. Jack Keese and his research team employed an innovative use of sulphur and heat with the paint.

This Issue

TTI’s Research Umbrella: Safer Transportation in the Storm

Volume 46, Number 2
June 2010
Issue Overview

On this page:

• The Hot-Melt Plastic Stripe as a Pavement Marking Material

]]> http://tti.tamu.edu/2010/06/01/then-ttis-contributions-to-pavement-marking-started-early/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