Diverging Diamond Interchange project wins 2025 ACEC Engineering Excellence Award

The American Council of Engineering Companies (ACEC) of Oklahoma has named Garver and the Oklahoma Department of Transportation’s (ODOT) Diverging Diamond Interchange project as a 2025 Engineering Excellence Honor Award winner in the transportation category. 

Located in Tulsa, at the US-64 (Memorial Drive) and US-169 (Creek Turnpike) Interchange, the project retrofitted an existing diamond interchange to a diverging diamond interchange (DDI) configuration containing a unique pedestrian trail crossing. The interchange is heavily traveled, with nearly 50,000 cars a day passing over Memorial Drive and under the US-169 bridge. Before construction of the new interchange, an average of 134 crashes occurred at this location every year. 

This higher-than-average collision rate was due to deficiencies in the interchange. Due to population growth and development, increasing traffic congestion was also an issue. With the DDI retrofit, ODOT sought to increase safety for travelers and pedestrians and to improve traffic flow. With Garver as their partner in design and construction, the resulting project achieved those goals. 

“We worked closely with ODOT and the City of Tulsa to retrofit this interchange,” said Garver Oklahoma Roadway Leader Jenny Sallee, PE. “This is only the second DDI constructed in Oklahoma, the first in the eastern part of the state. It’s extremely successful and that’s due to great collaboration and partnership as well as to technical expertise.” 

Garver provided comprehensive services from preliminary engineering and public involvement to final construction plans, including preliminary alternative analysis and impact assessment; a virtual public open house; roadway, retaining wall, and drainage design; GIS; VISSIM traffic modeling; traffic design and construction sequencing. . 

The team successfully navigated the complexities of designing within a constrained site: they designed the retrofit interchange without closing ramps or acquiring any additional right of way. They also ensured that  two lanes in each direction on Memorial Drive remained open during construction. 

Already on a fast-track schedule, Garver delivered the completed project two months faster than anticipated. By eliminating left turns across traffic and reducing speed through the interchange, a 14% reduction in overall collisions and 44% reduction in injuries and fatalities is expected, significantly improving safety for the traveling public, as ODOT desired. 

The pedestrian crossing of the retrofit interchange is designed to meet trail standards which accommodates walkers, runners, and cyclists. Due to the existing constraints and the retrofit nature of improvements, a central median refuge area would not have been adequate to work with typical pedestrian crossing patterns. Therefore, a separate signal crossing phase specifically designed for the trail was established between the two central refuge islands, effectively reducing crossing distance and time while improving safety for pedestrians. Even with the separate trail crossing signal phase, geometric improvements and signal timing upgrades to the interchange still improve travel times, reducing delays during peak morning and afternoon periods by 20-25%.

In addition to receiving an EEA from ACEC Oklahoma, commuters have responded positively to the interchange, appreciating the benefits of improved traffic flow, in news reports and comments. “That’s the ultimate reward,” Sallee said, “knowing that the project has made life better for the people in the community.”