Many states have begun to build two new types of intersections to help with traffic congestion and safety; Roundabouts and Diverging Diamond Interchanges. When you drive across the United States you can experience these new intersections in states like Missouri, Utah, New York, Tennessee and Wyoming to name a few.
Minnesota’s Department of Transportation opened Minnesota’s first diverging diamond intersection in October of 2013 in Pine Island, MN and opened a second one on October 16, 2013 in the Baxter/St. Could area.
Diverging Diamond Interchanges (DDI’s)
A Diverging Diamond Interchange (DDI), also known as a Double Crossover Diamond Interchange (DCD), is becoming more common where intersections meet highways. DDI’s/DCD’s are built above the freeway or highway, and require less land to be built on. It also reduces the amount of time needed for traffic to get through the intersection by reducing the number of perpendicular intersections at each interchange. Pedestrians also benefit by having less corners to navigate. The pedestrian has access on each side of the intersection and a main crosswalk access is in the middle of the intersection. Concrete barriers provide protection to the pedestrians from potential harm. The cost of building a DDI is far less than a conventional loop and ramp intersections.
Roundabouts are a circular intersection with a central island. Traffic travels in a counter clockwise motion. Approaching traffic must yield to vehicles already in the roundabout. Roundabouts eliminate intersection conflicts because there is no perpendicular or opposing direction turns to have to deal with like at a normal four-way stop intersection.
European cities have used various types of roundabouts since about the 1900’s. Cities and townships in Minnesota are beginning to use more roundabouts to control intersections. Roundabouts reduce crashes at busy intersections where accidents occur at a higher rate or where more than two intersections come together. Accidents at roundabout intersections have been known to be decreased by 39 percent for all crashes and decreased by as much as 89 percent for fatal crashes. Roundabouts provide smoother traffic flow. Also, when traffic is not idling at an intersection, vehicle emissions and fuel consumption is reduced by as much as 30%
When approaching a roundabout:
- Slow down as you approach the roundabout.
- For multi-lane roundabouts, as with any intersection, get into the appropriate lane as you approach the roundabout.
- Yield to pedestrians and bicyclists crossing the roadway.
- Watch for signs or pavement markings that require or prohibit certain movements.
- When entering a roundabout, yield to vehicles already in the roundabout. Do not cross into the roundabout until all traffic from the left has cleared.
- After entering the roundabout, drive in a counter-clockwise direction until you reach your exit.
- Do not stop, pass or change lanes within a roundabout.
- If an emergency vehicle approaches, exit the roundabout immediately and then pull over.
Since diverging interchanges have reduced traffic delays by 60 percent, improved safety to pedestrian and bicyclists’ access and lowered construction costs, MN Dot will continue to build DDI’s throughout the state where this type of interchange fits the areas traffic needs best.
Source: Minnesota Drivers Manual