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Roundabouts: Practical yet polarizing

ASU professor studies roundabouts to ensure maximum safety, efficiency.
June 29, 2017

Roundabouts a contentious traffic feature in AZ, but an ASU professor found that they're safer, more efficient than traditional stops

Traffic roundabouts are like broccoli. Many of us don’t like them, but they’re good for our driving diets.

In the right conditions, they increase safety, lower crash severity, reduce traffic delays and can even reduce greenhouse gas emissions, says Mike Mamlouk, a professor of civil, environmental and sustainable engineering at Arizona State University’s Ira A. Fulton Schools of Engineering.

But despite their demonstrated safety in other states, they’re a highly polarizing traffic feature in Arizona, which is why Mamlouk decided to study their effects in the Grand Canyon State with former ASU graduate student Beshoy Souliman. Their research was funded by the National Transportation Center at Maryland, of which ASU is a consortium member.

Since modern roundabouts were first built in the United States in the 1990s, they’ve been constructed in most U.S. cities. In Arizona they began popping up more recently — in 2006. Today, the state has around 80 roundabouts, mostly in single-lane and some in double-lane configurations.

Mamlouk and Souliman studied 17 roundabouts in Phoenix, Scottsdale, Sedona, Cottonwood and Prescott to evaluate their effect on crashes and their severity.

They collected data on traffic volume and number and severity of accidents in an equal number of years before and after conversion from a stop sign or traffic signal to a roundabout. Additionally, they looked at crash severity and cost levels from damage only ($11,000 average) to fatality ($1.5 million average).

Modern roundabouts (left) are the newest traffic control system on our roadways, and smaller than older rotaries or traffic circles (right).

Modern roundabouts (left) are the newest traffic-control system on our roadways and smaller than older rotaries or traffic circles (right). Photo courtesy of Melissa Kay Photography, TripAdvisor

 Stops vs. roundabouts

Intersections are dangerous places for drivers. Almost half of all traffic collisions in the United States happen at intersections.

Transportation engineers have found that if intersections are designed to be more forgiving — especially for distracted drivers who may run red lights or stop signs — they can minimize accidents or reduce accident severity when drivers make mistakes.

Roundabouts are one solution to this problem. In a roundabout, drivers are required to yield to cars already in the circle before they can merge, and raised lane splitters and medians help reduce traffic speed.

This configuration eliminates the potential for head-on and right-angle crashes.

“If a motorist runs the red light at a signalized intersection or does not stop at the stop sign, the vehicle will be on the path of crossing vehicles or opposing vehicles when making a left turn, which may result in a major accident,” Mamlouk said. “However, if a motorist enters the roundabout and does not yield to vehicles already in the circle, vehicles will crash at a small angle, causing a low-severity accident.”

Roundabouts have fewer dangerous conflict points, making accidents less likely to occur and less severe when they do occur.

Roundabouts have fewer dangerous conflict points, making accidents less likely to occur and less severe when they do occur. Graphic courtesy of Mike Mamlouk

 Reduced traffic speed as drivers approach the roundabout intersection also reduces crash severity.

He added that the geometry of a roundabout means there are fewer conflicting points where crashes can occur. So in addition to reducing the severity of crashes, roundabouts reduce the chance of crashes.

Mamlouk and Souliman found that single-lane roundabouts decreased the total accident rate by 18 percent per year, and decreased the injury rate by 44 percent per year.

To Mamlouk’s surprise, two-lane roundabout accidents increased the total accident rate per year by 62 percent. However, these accidents were less severe and the injury rate decreased by 16 percent.

There was one fatality at a single-lane roundabout before conversion and one fatality at a double-lane roundabout before conversion. After roundabout conversions there were no fatalities for both single- and double-lane roundabouts. Also, the average accident cost per intersection decreased for both single- and double-lane roundabouts.

Constructing roundabouts in the right conditions

Though safety improved at the roundabouts the researchers studied, they are effective only in the right conditions, called warrants, which include levels of traffic volume, traffic fluctuation during the day, peak-hour factor, pedestrian volume, school crossing, crash experience and roadway network.

The Federal Highway Administration’s Manual on Uniform Traffic Control Devices lists warrants for various intersection control types, except roundabouts. Guidelines exist, but the decision is often more subjective than decisions to install stop signs or traffic lights.

“Although no warrants are currently available, engineers use the available guidelines together with previous experience to decide if a roundabout is suitable at an intersection,” Mamlouk said. “Warrants make the decision easier, consistent and more objective.”

When placed correctly, roundabouts also result in non-safety improvements for drivers.

“Instead of stopping at the stop sign or at the red light when no other vehicles are at the intersection, roundabouts allow motorists to proceed with caution without stopping, allowing for free-flow movement,” Mamlouk said. “Reducing stopping has the benefit of increasing the intersection capacity and reducing traffic delay and greenhouse gas emission.”

However, when poorly placed, roundabouts can cause increased traffic congestion and crash rates.

Warrants also help determine when a roundabout is no longer needed as traffic conditions change.

Educating the public

Mike Mamlouk

Professor Mike Mamlouk

As Mamlouk’s research concludes, he is presenting his findings to public officials to help them carefully assess the specific conditions at intersections before converting them to roundabouts.

As he and other researchers continue to observe and report on roundabout performance, warrants adhering to the Manual on Uniform Traffic Control Devices will begin to be developed.

Mamlouk also hopes to work with public agencies to help educate drivers about the proper use and advantages of roundabouts.

With only 80 roundabout intersections among the thousands of roadway intersections in the state, they’re still fairly rare, and using them correctly can take some practice

“When they introduced the traffic signals in the 1920s, it took people several years to get familiar with the three-color system and understand the rules of the traffic signal,” Mamlouk said. “I am sure people will get familiar with roundabouts with time and experience.”

Just as with the basics of using the traffic signal — now a no-brainer to alert drivers — the rules of the roundabout are simple:

“Remember, when getting close to a roundabout, slow down, look left, let vehicles already in the roundabout pass first, and then proceed with caution,” Mamlouk said.

Monique Clement

Communications specialist , Ira A. Fulton Schools of Engineering

480-727-1958

 
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Uniting lost voices

ASU professor is co-editor of new Bioarchaeology International journal.
June 30, 2017

New bioarchaeological journal gives scientists a platform to share research on past lives and deaths in international forum

Bioarchaeology is a young but quickly growing field that studies how people from the past lived and died, and is most often described as a combination of biological anthropology, archaeology and social theory. However, this field also faces a problem: There are many different approaches to and even definitions of bioarchaeological research, making it difficult to share findings across disciplines, organizations and geographic borders.

cover image of Bioarchaeology International

Bioarchaeology International is a new, first-of-its-kind journal specifically dedicated to bioarchaeological research. Its goal is to help unify perspectives by providing a space for peer-reviewed articles and encouraging global discussion. The quarterly publication, which will appear in print and online, will release its inaugural issue on June 30.

“This is a platform for bridging the archaeological focus on mortuary behavior, ritual and cemetery organization with the more biological focus on skeletal remains,” said Brenda Baker, co-editor of the journal. Baker is an associate professor in Arizona State University’s School of Human Evolution and Social Change and a bioarchaeologist with the school’s Center for Bioarchaeological Research.

Bioarchaeology is unique in its interdisciplinary nature, investigating both the material and the biological evidence left behind in the grave. Although different factions may emphasize one side over the other, in the journal’s introductory article, BakerBrenda Baker is an associate professor in the School of Human Evolution and Social Change, a core faculty member of the school’s Center for Bioarchaeological Research and director of the Bioarchaeology of Nubia Expedition. Her research encompasses bioarchaeology, mortuary archaeology, human osteology and paleopathology, emphasizing the investigation of human skeletal remains within their archaeological contexts to reconstruct past lifeways and the health status of ancient people. and her co-editor Sabrina Agarwal of the University of California Berkeley argue that integrating these aspects is what allows researchers the clearest understanding of ancient people’s life experiences.

Two of the papers that will be published in the first edition of the journal, for example, explore how the dead were handled by the living in Neolithic Ireland and Turkey. By studying both how graves were used and how bodies were treated, researchers are able to learn about the social significance behind mortuary traditions.

These bioarchaeologists are answering questions about past societies that are of special interest to today’s modern readers, social scientists and policy makers, such as how humanity has historically responded to challenges like disease, climate change, migrations and inequality. With current research trends focusing on the life experiences of individuals and the use of rapidly advancing techniques in biogeochemical analysis and molecular biology, the journal promises to be a wealth of relatable, relevant and cutting-edge findings.

Although bioarchaeology has many branches, with Bioarchaeology International, these schools of thought now have a vetted public forum to explain their research, exchange ideas and stand together in their common goal to better understand the human experience.

The first edition of Bioarchaeology International will be available at bioarchaeologyinternational.com on June 30. Read the open access introduction to the journal.

The journal is currently accepting submissions, particularly those from around the globe using varying scales of analysis that focus on theoretical and methodological issues in the field. More information, including how to submit to the journal, can be found at bioarchaeologyinternational.com.

Mikala Kass

Editorial Communications Coordinator , School of Human Evolution and Social Change

480-965-0610