Diverging Diamond Interchange

A Diverging Diamond Interchange (DDI) is the intersection of Trunk Highway 15 and County Road 120.

A Diverging Diamond Interchange (DDI) allows two directions of traffic to temporarily cross to the left side of the road. A DDI moves high volumes of traffic through an intersection without increasing the number of lanes. This movement provides easier access to a busy divided highway.

Why a Diverging Diamond?

The area around the intersection has been rapidly developing. The CentraCare Plaza healthcare facility is a major traffic contributor west of Hwy 15.  The city of Sartell had over $70 million in new office and medical facility construction in 2009, with more planned. The retail development east of Hwy 15 (Sam’s Club, Wal-Mart, etc.) was just beginning construction and was expected to bring large amounts of new traffic to the area. The existing intersection already had a high crash rate and experienced congestion during the peak hours.

A DDI reduces congestion by allowing traffic to keep moving through an intersection. It also improves safety by allowing free flowing turns when entering or exiting the roadway, eliminating left turns against oncoming traffic and reducing the number of traffic signal phases.

The DDI provides better sight distance at turns and fewer chances to conflict with other vehicles, resulting in fewer crashes. The signal cycles are very short because there are no left turns, providing better mobility. The DDI is expected operate at a high level of service with few crashes and improved signal efficiency.

Motorists on Stearns CR 120 will proceed through the first traffic signal, and follow their lane to the opposite side of the road. Drivers accessing Hwy 15 will turn left onto the ramps. Through traffic will continue to the second traffic signal and follow their lane back to the right side of the road.

Pavement markings, signs and signals direct motorists through the intersections.

Motorists on Hwy 15 will use the ramps and traffic signals to access CR 120.

Pedestrians and Cyclists will use sidewalks to access a center pedestrian island in the middle of the bridge. The walkway is protected with concrete barriers.

Pedestrians cross only one direction of traffic and cross fewer lanes.

MNDOT Diverging Diamond Interchange website