TRANSPORTATION MATTERS for IOWA

Here’s how to cross U.S. 20 from northbound Poplar Avenue. 

Drive through the interchange from southbound Poplar Avenue.

What is a “reduced-conflict” intersection?

Reduced-conflict intersections are designed to reduce the number of conflict points where vehicles can crash into each other. Our neighboring states of Minnesota, Wisconsin, and Missouri have multiple intersections like these that have proven to be successful in decreasing fatalities and injuries caused by broadside crashes on four-lane divided highways.

Why do they work?

The updated intersection improves mobility and increases safety by reducing the number of points where vehicles can inadvertently come into contact with other vehicles by 50 percent.

Willy Sorenson, an Iowa DOT traffic safety engineer, is all about the numbers when it comes to reducing crashes. He said, “A typical four-lane divided highway intersection has 42 possible vehicle conflict points. Reduced-conflict intersections accomplish just what the name would imply, reducing conflict points to as few as 24. Simply put, this type of intersection makes it more difficult for drivers to crash and when they do crash, those crashes will be less severe.”

The red dots on this diagram represent the potential for the most severe types of crashes, the blue and yellow dots are typically less severe. Reduced conflict intersections improve safety because they have significantly fewer potential crash or conflict points than conventional intersections.

How do they work?

Think back to the parenting scenario. Like separating your conflicting children and giving them time to think, this type of intersection separates vehicles and gives drivers time to think about one driving activity at a time. It works like this: when you are turning from a side street to a four-lane highway, you only have to be concerned with one direction of traffic on the highway at a time. You don’t need to wait for a gap in both directions to cross the major road.

In a reduced-conflict intersection, drivers on the side road wanting to turn left or cross the four-lane highway will turn right onto the highway, merge into the left lane and then make a U-turn at a designated median opening. The way the pavement is set up, you cannot make a left turn onto the four-lane highway or cross both directions of traffic. While this might sound like it will take you longer to turn, generally, the delay caused by a traffic signal or just waiting for traffic to clear at a two-way stopped-controlled intersection is greater than the delay caused by the reduced-conflict intersection.

Traditional four-lane divided highway intersections have an elevated risk of severe right-angle crashes (commonly called “T-bone” crashes) when you are crossing all four lanes of traffic. The driver from the side street needs to keep track of traffic in both directions at one time to cross the four-lane divided highway or make a left turn. In a reduced-conflict intersection, when vehicles do come into contact with each other, the severity of crashes is much less compared to traditional intersections.

What are the benefits of a reduced-conflict intersection?

• Improved safety — Studies show a 70 percent reduction in fatalities and a 42 percent reduction in injury crashes where a reduced-conflict intersection is used.
• Faster to build — reduced-conflict intersections can be designed and built in approximately one year. Interchanges typically take 3-5 years and are not practical at all locations.
• Lower cost — reduced-conflict intersections are often less expensive than constructing and maintaining an intersection with a traffic signal and are a fraction of the cost of building an interchange.

For more information on reduced conflict intersections, go to https://iowadot.gov/traffic/reducedconflictintersection.