Iowa DOT rolls out its first reduced-conflict intersection

(The Center Square) – Benefits of Iowa Department of Transportation’s first reduced-conflict intersection include cost savings, district staff say.

The department said on its website that the new intersection, for U.S. 20 and Poplar Avenue near Fort Dodge, was opened to reduce crashes and injuries, which may be getting busier with the opening of a travel plaza.

Reduced-conflict intersections change the way cross-traffic flows through an at-grade intersection with a high-speed expressway. On traditional four-lane divided highway intersections, drivers need to keep track of traffic in both directions at the same time to cross or make a left turn. In a reduced-conflict intersection, drivers on the side road who want to turn left or cross the four-lane highway turn right onto the highway, merge into the left lane and then make a U-turn at a median opening. They can’t turn left onto the four-lane highway or cross both directions of traffic. The department posted videos showing the change.

Benjamin Hucker, a District 1 traffic operations engineer with Iowa DOT, told The Center Square that reduced-conflict intersections save taxpayers money by decreasing the potential for crashes.

“Every time there is a crash, public resources are expended for the crash response and traffic can be significantly delayed, increasing user delay costs from emergency detours or being slowed down in a traffic jam,” Hucker said. “Reduced-conflict intersections have been shown to reduce fatal crashes by 70% and injury crashes by 42%, which translates into a societal cost savings from both a monetary and emotional perspective.”

The intersections also decrease direct costs, he said. Iowa DOT says each intersection is unique; thus, there are no “standard” cost estimates for savings between reduced-conflict interchanges and traditional expressway interchanges. Hucker said retrofitting a reduced-conflict intersection is about 10% of the cost of a new expressway interchange. While a typical new interchange costs about $15 million, the cost to retrofit this Webster County intersection into a reduced-conflict intersection is roughly $1.5 million, he said.

The department said the intersections are also often less expensive than constructing and maintaining an intersection with a traffic signal. The intersections take about a year to design and build while interchanges typically take a few years.

Hucker said that usually a reduced-conflict intersection can be constructed within the existing highway right-of-way. If another right-of-way is needed, it’d typically only be a small sliver to allow for off-set right turn lanes, he said.

“By contrast, a typical diamond interchange requires several acres of additional right-of-way, not to mention the cost of a new bridge and additional ramp pavement,” he said. “At applicable locations, reduced-conflict intersections can not only save money, but keeps valuable Iowa farmland in production.”

The intersections will involve changes in side-road traffic patterns and maintenance and snow removal operations, but it won’t be in a significantly negative way, Hucker said.

“Some drivers may initially perceive that it takes a few seconds longer to navigate the intersection by turning right and then utilizing the U-turn lane in the median, but in reality, it may be quicker because they don’t have to wait for a gap to cross traffic; they simply have to find a gap to merge with traffic and then change lanes into the median U-turn lane,” he said.

Hucker said he isn’t aware of any reduced-conflict intersections on the local system either and this is the only one the department plans to open this year.

Some other states, like Minnesota, Wisconsin and Missouri, have several.

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