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Novel intersection treatment scrutinized

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Novel intersection treatment scrutinized

Three men stand in a group photo with a highway behind them.

MU Engineering researchers work onsite collecting data on the j-turn intersection at U.S. Highway 63 and Deer Park Road. From left are Igor Caus, a recent graduate who earned a bachelor’s degree in civil engineering in May; Kevin Koines, a rising senior in civil engineering; and Henry Brown, a research engineer in civil engineering.

In an effort to increase motorist safety and traffic-flow efficiency, the Missouri Department of Transportation (MoDOT) has implemented some novel intersection treatments on the state’s roadways. Two of these designs have been selected for implementation on roadways in or near Columbia. A “j-turn” constructed on U.S. Highway 63 and Deer Park Road south of Columbia has been operational since August of last year, and a “diverging diamond” at the Stadium Boulevard and Interstate 70 interchange is scheduled for completion late this fall.

A research team headed by Praveen Edara, MU assistant professor of civil and environmental engineering, was selected by MoDOT to evaluate the j-turn, a project being managed by Sawyer Breslow, a master’s student in Edara’s lab who will write his thesis on the project.

A diagram of a regular left turn versus a j-turn.

A conventional left turn onto a divided highway would require drivers to cross up to three lanes of traffic on U.S. Highway 63, as illustrated in the top image. A j-turn intersection would require drivers to turn left, then make a U-turn and merge, as shown on the bottom.

“Traffic on Highway 63 runs at 70 miles per hour,” Edara said. “Motorists making a left turn from a side street must look for gaps in both directions of 63. Any misjudging of gaps could lead to severe right angle crashes. MoDOT is using the j-turn to improve safety of such left turn movements on high-speed rural highways.”

The j-turn requires left-turning motorists from both directions to first turn right and then make a u-turn “downstream” to merge into traffic in the direction they intend to travel. Critics complain that j-turns add drive time, but advocates argue it may actually reduce it during peak traffic-flow since motorists will not have to wait for a safe gap in order to cross traffic.

“Even with a minor increase in travel time, the increased safety of j-turns makes them desirable, especially at locations with a history of angle crashes,” Edara said.

The issue is of special concern in Midwest states where rural expressways are prevalent, and the researchers believe study results will support MoDOT’s decision to install a j-turn on Hwy. 63.


Assistant Professor Praveen Edara

“We’re looking at a couple of things,” said Breslow, who led a team of students to gather data at the site using video monitoring and speed radar equipment. “How do people actually operate through them? Are they confused? How long are they waiting in the acceleration lane to merge?

“We’re also measuring some innovative safety measures such as gap availability, time to collision and time to intersection — things that have not been measured at other j-turn sites in the country. Our work will be an original contribution to the body of work on j-turn evaluations.” Breslow said.

Sawyer Breslow

Sawyer Breslow

Edara said that since the group was not able to monitor the Hwy. 63 site before the j-turn was installed, they requested a control site for comparison.

“MoDOT recommended the intersection of Highway 63 and Calvert Hill Road as a control,” Edara said. “Using it as a comparison, we can actually demonstrate how well the j-turn is working.”

In addition to the collected site data the research group is analyzing, the MoDOT project also involves collecting motorist opinions on driving the j-turn. A survey will be available through the end of August for anyone who drives the corridor and would like to share their impressions.

A diagram of a diverging diamond intersection.

A diverging diamond intersection eliminates the need to cross oncoming traffic lanes in order to access highway entrance ramps. Wikipedia photo

Edara has been researching novel intersection designs for the past 10 years. He did some seminal research, with the Federal Highway Administration’s Turner Fairbank Highway Research Center, on the diverging diamond interchange through simulation models and published its safety and mobility benefits. His research has made him a national expert in novel intersections. The City of Columbia interviewed him about the diverging diamond interchange now under construction.

Carlos Sun, professor of civil and environmental engineering at MU who is a partner on the project, said that the group finds the research rewarding.

“There is joy in working on projects that have such significant impact on people’s lives,” Sun said.

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