Innovative Geometric Design

Across the Country, DOTs are faced with a multitude of challenges in delivering transportation improvements.

Traffic volumes are growing substantially. Right-of-way costs are excessive. Impacts on resources and communities are deeply scrutinized. As a result, innovative geometric design solutions are highly valued. Wallace Montgomery is a recognized leader in the Design of Innovative Intersections and Interchanges. We support the Alternatives Evaluation process during the Planning phase with a highly effective “Thinking Outside the Box” mindset. We deliver on Final Design while addressing important issues such as Maintenance of Traffic, Roadside Safety and Traffic Control Device Design. We integrate Pedestrian and Bicycle considerations for safety and access. As a result of our emphasis on innovation, we are providing peer reviews throughout the United States on Innovative Interchange Design.

The Diverging Diamond Interchange (DDI) is similar to a standard diamond interchange, except that in a DDI, the arterial roadway switches to the left side of the road between the ramp-terminals at two at-grade crossover intersections. The DDI is a design that can significantly improve safety and operations at a very low cost. The DDI is best used when there are heavy left turn movements and/or unbalanced thru movements. We are seeing that the DDI may be appropriate for many other turning movement combinations due to the efficiency of lane use. The DDI requires fewer lanes on (or below) the bridge structure.

Superstreets (or J-Turns) are arterial roadways that prohibit thru or left turn traffic from side roads, reducing crossing conflicts. Side road traffic must turn right and then make a U-turn beyond the intersection. Superstreets generally signalize all intersections and U-turn movements; however, if traffic volumes are low, signals are often not warranted. When a corridor is designed with a series of Superstreets, an advantage is that traffic signals can be coordinated independently allowing for “perfect progression.” Traffic operations will notably improve at intersections with low thru movements from the side road. Superstreets improve safety in both urban and rural environments. (SuperStreets is the Urban application, while J-Turns is the Rural application of the same concept.)

Continuous Flow Intersections (CFI) have some or all left turns initially occurring prior to the main intersection into a short service road. At the main intersection, left turns do not conflict with opposing thru traffic, improving traffic operations and reducing conflict points. The CFI can have an estimated 50% greater capacity than conventional intersections and improved traffic flow for all movements. It is ideal for congested intersections where grade-separation may be the only other viable option.

Innovative Geometric Design has three principal benefits. IGD can improve safety, improve operations for all users and reduce costs. When designed and applied correctly, IGD delivers on all three benefits concurrently.