1. Double Crossover Diamond Interchange
Heather Hunt
April 8, 2014

2. What subjects from class does this topic cover?
Engineering design to promote/increase safety
Building safer roads
Road designs that influence human behavior

3. What is a Double Crossover Diamond Interchange?
Double Crossover Diamond (DCD) Interchange or Diverging Diamond Interchange (DDI)
Roadway concept developed in the 1970’s
Alternative to the conventional diamond interchange

4. How does it work?
Allows right-turning traffic to merge onto expressway ramp
Brings thru and left-turning traffic to the other side of the road
Left-turning traffic merges onto the expressway ramp
Brings road back to original side
Traffic exiting expressway merges into their respective lanes
Pic of DDI and movements

5. Current examples First DDIs built in France in 1970’s Seclin, France
Versailles, France
Le Perreux-sur-Marne, France

6. Examples (cont.) First US DDI Springfield Missouri
I-44 and Missouri Route 13
Lexington KY
US 68 and KY 4

7. Why choose a DCD interchange?
Reduced construction time/cost
Good for areas with limited space for expansion
Reduces congestion
Two phases
More green time
Increased safety

8. How does it influence highway safety?
Reduction in the number of conflict points
14 conflict points
2 crossing conflicts
26 conflict points
4 crossing conflicts

9. Highway safety (cont.) No opposing left turns DDI in France
Traffic-calming features
Slower speeds
Reduced accident severity
Wrong-way movements eliminated
Lack of increase in driver errors
DDI in France
Only 11 minor injury crashes in 5 years
Comparable US conventional intersection
21-23 injury/fatal crashes

10. Highway safety (cont.)

11. Highway safety (cont.)

12. Highway safety- Influencing driver behavior
Roadway geometry prevents certain movements
Signs and signals help drivers understand environment
Despite concerns, there have not been many cases of driver confusion leading to wrong-way movements
Slower speeds allow better observation of surroundings

13. Pedestrians and bicyclists
Pic(s) of pedestrian movements
More efficient for pedestrians
Have to cross in two phases
More pedestrian refuges and crossing points
Some DDI have pedestrian paths along the median of the intersection
A barrier-protected alternative
Experience fewer conflicting traffic streams