Diverging Diamond Interchange
The bridge at Route 65 and Battlefield Road had been scheduled for replacement because of deterioration and non-compliant freeway clearance. A diverging diamond interchange (DDI) design was requested for its innovative ability to improve traffic flow through its use of traffic signals, gentle curving lanes, and striping to route drivers to the opposite side of the road.
DDIs eliminate left turns against traffic, and, once through, drivers are brought safely back to the correct side of the road. Other reasons for selecting the DDI design include the following:
- DDIs provide excellent capacity and traffic operations benefits, predominantly for areas with high left-turn volumes.
- DDIs provide safety benefits by minimizing the likelihood of right-angle crashes, and they also reduce speeds through the interchange.
- The two-phase operation effectively makes the left-turn movement a free-flow movement, rather than requiring a separate phase-and-yield condition.
- For capacity improvement projects, costs are lower and construction times are shorter.
Olsson was assisted by subconsultants Hanson Professional Services (bridge structural) and TREKK (lighting, stormwater, and signing and striping design). In addition to being the lead consultant for the project, Olsson provided the following design elements:
- Urban interchange geometrics
- Bridge structural
- Traffic operations analysis
- Traffic signals
- Intelligent Transportation Systems
- Traffic maintenance
- Construction phasing/constructability
The team developed four specific design solutions that provided great benefits to the project. These solutions included the following:
- Three lanes of traffic in each direction across the bridge to provide even more added capacity than what the Missouri Department of Transportation (MoDOT) originally planned.
- To accommodate a traffic signal east of the bridge, the team modified the profile to provide a flatter slope through the intersection, while still avoiding negative impacts to the adjacent properties and utilities.
- The team designed a temporary DDI configuration to be used throughout construction to accommodate the area’s high traffic volumes. It allowed for a tremendous increase in capacity and reduced delays from what would have occurred with traditional, reduced-interchange operations during construction.
- Olsson’s design to replace the existing bridge required installing new piers in the freeway median, which necessitated closing the inside traffic lanes. Recognizing the continued need for six lanes of traffic throughout construction, Olsson’s design replaced the existing shoulder beneath the bridge with a wider, full-depth pavement shoulder that could be used as a third lane and would maintain the needed freeway capacity.
The DDI project was completed in the fall of 2015.