U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
The original, conventional diamond interchange averaged more than 100 crashes a year from 2004 to 2008. In addition, traffic in the left turn lanes often caused 1 to 3 mile back ups in the through lanes.
Installation of the Nation's first Diverging Diamond Interchange with widespread outreach to gain public acceptance by highlighting the mobility and safety enhancements inherent in the design.
Jeffrey Shaw, P.E.
Mark Doctor, P.E.
The previous conventional diamond interchange at this location averaged over 100 crashes a year from 2004-2008,2 so safety was a primary concern. Another important concern was delay. The spacing and location of the adjacent signals along Missouri 13 meant that, during peak traffic, the signalized left turns onto the freeway would frequently back up into the through lanes. On a normal day, backups could reach nearly a mile. During events at the nearby fairground, backups could be as long as 3 miles, creating lengthy delays and contributing to unsafe conditions.3 Furthermore, because this DDI was the first of its kind in the United States, public acceptance was also a factor. Missouri DOT (MoDOT) had to convince citizens that the facility was going to provide real improvements by reducing congestion and improving safety.
Computer Simulation of the Proposed Interchange
Source: DDI Case Study Video FHWA-SA-14-047
To address public concerns about safety and delay, the agency used a simulation tool and projected traffic volumes over the next 25 years to model the new interchange. MoDOT then created a video explaining how the DDI could reduce delay by 10 to 35 percent through to 2035 and improve safety by eliminating just over 50 percent of vehicle conflict points.4
Cost-effectiveness also was an important factor in MoDOT's decision to build the DDI. The agency chose the DDI design because it didn't require a new bridge, could be completed in 6 months, and, at $3.2 million, was one-third the cost of the next best alternative.5
In a post installation MoDOT driver survey 95 percent of Springfield residents agreed the DDI resulted in a less congested roadway.6 Less congestion also meant fewer crashes. Total crashes declined 46 percent when comparing the average across the 5-year baseline to the one-year post-construction period; minor injury crashes decreased 72 percent.7 Pedestrians and bicyclists also have benefitted from the DDI; they now can use an illuminated and protected median walkway to cross the interchange.
1 Missouri DOT, Diverging Diamond Interchange Performance Evaluation (I-44 and Route 13), OR11-012 (2011). Available at: http://library.modot.mo.gov/RDT/reports/TRyy1013/or11012.pdf
2 Missouri DOT, OR11-012 (2011). [ Return to note 2. ]
3 Interview with Don Saiko, Springfield, MO, November 1, 2013. [ Return to note 3. ]
4 Missouri DOT, OR11-012 (2011). [ Return to note 4. ]
6 Missouri DOT, Diverging Diamond Interchange - Results from the Right Transportation Solution Survey, January 2010. Available at: http://library.modot.mo.gov/RDT/reports/TRyy1013/orb10005.pdf [ Return to note 6. ]
7 Missouri DOT, OR11-012 (2011). [ Return to note 7. ]
This Fact Sheet is a companion to the Video Case Study (FHWA-SA-14-047)