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Intersections and Interchanges

Diverging Diamond Interchanges | Roundabouts | J-Turns | Single-Point Interchanges


An intersection describes a situation where two or more roads cross at the same level. An interchange is a grade-separated intersection (one road passes over another) with ramps to connect them. Factors such as safety, cost, capacity, environment, development and politics can vary at every site; consequently there are hundreds of unique, one-of-a-kind interchanges worldwide. Interchanges are designed to fit specific local conditions and meet driver expectations.


Some basic types of interchanges are: diamond, directional and cloverleaf.


  • Diamond interchanges are the most common type and are suitable in both rural and urban areas. They can become congested, though, by a high volume of left-turning movements on the crossroad, and they often include signals that control ramp access to and from the crossroad. Spacing between the ramps is critical for efficient movement of traffic through the interchange.

  • Directional interchanges accommodate high-volume turning movements where two freeways intersect. Direct ramp movements reduce travel distance, increase speed and capacity, eliminate weaving and avoid the need for “out-of-direction” travel on a loop. These interchanges are costly to construct due to the increased number and length of ramps and the number of bridge crossings.

  • Cloverleaf interchanges can be used where two high volume freeways intersect. Loop-ramps are used to accommodate left-turning movements. However, this configuration provides short weaving areas for traffic entering or leaving the interchange. A cloverleaf interchange occupies a relatively large area of right of way.

Diverging Diamond Interchange


Diverging diamond interchanges (DDI) are diamond interchanges that more efficiently handle heavy left-turn movements. While the ramp configuration is similar to a traditional diamond interchange, traffic on the crossroad moves to the left side of the roadway for the segment between signalized ramp intersections. The nation’s first DDI was built by MoDOT in Springfield in 2009.



This animation shows how Diverging Diamond interchanges

help keep traffic flowing.




A roundabout is a circular traffic intersection featuring yield control on all entering roadway legs, one-way continuous flow within the circulatory roadway, channelization of the approaching roadways, and appropriate geometric curvature to keep circulating speeds low. Roundabouts may contain as few as three legs; however, roundabouts with more than four legs are not uncommon.



Roundabouts are safer and easier to navigate than a traditional intersection.


J-turns are relatively new to Missouri, offering a low-cost way to bring a significant safety improvement to median crossings from a sideroad to a divided highway. J-turns eliminate some or all traffic movements through the median. Traffic on the sideroad is forced to turn right onto the main roadway rather than go straight through the median. Through and left-turn movements from the sideroad are completed through a downstream median u-turn located approximately 600-1,000 ft. from the primary intersection.


Get more information on J-Turns




J-Turns are safer than old fashioned intersections


Single-Point Interchanges  

Single-point urban interchanges (SPUI) were first constructed in the early 1970s, and are used most often in tight right of way situations. Their primary feature is all four turning movements intersect at a common point. They are costly to build because of the large bridge structure that is required.


Get more information on Single Point Interchanges here.


single point interchange
Enhanced Pedestrian Crossings  

MoDOT is using a new enhanced pedestrian crossing system at locations across the state. The new crossings make it easier for pedestrians to safely get across busy roads at locations that are not at signalized intersections. It also minimizes traffic delays, because it only operates when a pedestrian activates it.


Get more information on Enhanced Pedestrian Crossings here.


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