Twists, Turns and Turbines: How Complete 540 (R-2828) Is Keeping Raleigh Rolling

A turbine-style interchange connects I-40, Toll N.C. 540 and I-42. (SkySite Images)

“Cities have the capability of providing something for everybody, only because, and only when, they are created by everybody.”

– Jane Jacobs (author, The Death and Life of Great American Cities)

When the new 18-mile, six-lane Toll N.C. 540 extension in Raleigh, N.C., opened on Sept. 25, 2024, motorists instantly experienced something rarely felt when traveling along this roadway during peak travel times: relief from congested surface streets and arterials, and faster travel times between communities.

The extension, located in the southern half of the Raleigh metro area, is a key part of the Complete 540 project, representing a significant leap in North Carolina infrastructure development. It extends the surface transportation network by connecting major highways and enhancing mobility throughout surrounding regions.

WSP was gratified to have worked with the North Carolina Turnpike Authority (NCTA) and North Carolina Department of Transportation (NCDOT) as lead firm on the design team for R-2828, representing approximately half of the new 18-mile extension.

The project accommodates future transit needs and implements sustainable design practices. Local access roads, ramps and interchanges were designed to handle high traffic volumes, future growth and environmental considerations. R-2828 lies within the Swift Creek Watershed, a protected area with stringent environmental requirements that were addressed. The project also includes the innovative two-level turbine-style interchange—a marvel in design and engineering that promises smoother, safer and more-efficient traffic flow.

WSP also serves as prime construction engineering and inspection firm for Phase 2 of Complete 540, a 10.8-mile extension of Toll N.C. 540 aimed at completing the circumferential highway around greater Raleigh. Construction for this phase began in May 2024, with an anticipated opening to traffic by late 2028, fully completing the Triangle Expressway and the 540 Outer Loop. The outer loop will serve as a critical connector for commuters, freight carriers and regional travelers, relieving congestion, reducing travel times and supporting planned economic growth by enhancing accessibility.

Taking a step back, the story behind the expansion began in the mid-1980s, when the region’s rapid growth prompted NCDOT to focus on converting the existing northern outer loop highway into a comprehensive loop encircling Raleigh.

The formal study of potential routes commenced in 2009, characterized by extensive public engagement and collaboration with environmental and regulatory agencies, which led to identification of several alternative routes. In June 2018, following the completion of the final environmental impact statement, NCDOT and the Federal Highway Administration issued their record of decision, formally designating the preferred alternative (bit.ly/3D4FeMk).

The design and construction contract for R-2828 was awarded to the Lane-Blythe Construction Joint Venture, which included WSP as the lead design firm, ensuring the project would proceed with a focus on innovative engineering solutions and sustainable development practices. This strategic selection and awarding process set the foundation for a successful expansion of the Complete 540 corridor, enhancing connectivity in and around Raleigh.

Engineering a Corridor for Connectivity and Sustainability

A turbine-style interchange was chosen to connect three major highways (I-40, Toll N.C. 540 and I-42) due to its efficiency in accommodating high traffic volumes and maintaining traffic flow even as vehicles enter and exit at multiple points.

The design provides a visually striking element that seamlessly integrates into the surrounding terrain, reflecting a commitment to both engineering excellence and environmental stewardship. The turbine-style interchange minimizes weaving issues and reduces conflict points, unlike traditional cloverleaf designs. By arranging the exit and entrance ramps in a circular, “turbine-like” formation, this design ensures smoother merging and separation of traffic.

Its unique design offers several advantages:

• Reduced Weaving and Enhanced Safety. The two-level turbine-style design reduces areas where vehicles must cross paths, significantly decreasing the likelihood of congestion and crashes. Additionally, the design includes wide shoulders and emergency pull-off areas, supporting safer responses to roadside incidents.

• Enhanced Flow. The design naturally encourages a steady flow of traffic, with vehicles merging seamlessly into their respective lanes without abrupt stops or slowdowns.

• Compact Footprint and Environmental impacts. Turbine interchanges typically require less land than traditional interchanges, making them a suitable option for areas with geographic or environmental constraints.

• Construction Benefits. The compact design required less land and grading than a traditional interchange, reducing the impact on local landscapes and simplifying the construction phase.

• Future Maintenance. The design strategically reduces the number of bridges within the turbine interchange, which significantly simplifies future maintenance. By minimizing bridge structures, the project lowers the complexity of inspections, repairs and potential closures leading to reduced long-term maintenance costs and operational disruptions.

Another crucial feature of this segment is the radial bridge design across the Juniper Branch stream. It represents a key structural element of the Complete 540 project, combining functionality with aesthetic appeal.

This design incorporates a series of outward-radiating supports, creating a fan-like structure that distributes weight efficiently while minimizing the environmental impact on the underlying ecosystem. By aligning with the natural contours of the landscape, the radial bridges enhance water flow and reduce erosion around the stream, preserving the integrity of the surrounding wetlands. This technical concept is estimated to have saved $1.3 million. These bridges improve connectivity and demonstrate an innovative approach to sustainable infrastructure in the Raleigh area.

In addition to choosing an alternative design concept that minimized watershed impacts, a comprehensive approach was implemented to fulfill environmental commitments within the Swift Creek Watershed, with special focus on protecting endangered species, including the Dwarf Wedgemussel and yellow lance mussel. The project team collaborated with environmental specialists at Three Oaks Engineering Inc. to carefully relocate these sensitive species from impacted areas.

Additionally, advanced stormwater management measures such as hazardous spill basins were introduced to capture and treat roadway runoff before it enters the watershed. The project also included reforestation and habitat restoration efforts to offset construction impacts, ensuring that native plant and animal species continue to thrive in the area. These efforts, combined with rigorous sediment and erosion control measures, reflect the project’s commitment to sustainable development and preservation of the Swift Creek Watershed.

Driving Social and Economic Growth for Raleigh

The opening of Complete 540 Phase 1 marks a crucial step in expanding greater Raleigh’s transportation infrastructure. The $1.3 billion project includes new interchanges at Holly Springs Road, Bells Lake Road, U.S. 401, Old Stage Road and N.C. 50.

The $1.2 billion Phase 2 project will extend the Triangle Expressway from I-40 to the existing Interstate 540 at I-87/U.S. 64/U.S. 264 interchange in Knightdale. Seven interchanges and 29 bridges will be built along the way, providing access to neighboring communities and protecting sensitive resources. Once operational, Complete 540 Phase 2 will mirror the remainder of the Triangle Expressway as a 70-mile-per-hour, six-lane all-electronic toll facility.

Beyond infrastructure, the Complete 540 project is a long-term investment in Raleigh’s social and economic vitality. The completed outer loop will improve connectivity across the Triangle region, reducing travel times and enhancing access to Research Triangle Park, Raleigh-Durham International Airport and nearby business hubs. These benefits extend to residents who will experience shortened commutes, improved safety and better access to amenities, while businesses will benefit from smoother logistics and an expanded customer base.

In shaping Raleigh’s growth, Complete 540 supports housing and community development along its corridor, laying the groundwork for new neighborhoods, retail centers and workplaces. The turbine-style interchange and strategic roadway design will accommodate growth while maintaining traffic flow, making the region attractive to businesses and improving quality of life for residents.

In addition, the toll system ensures that ongoing maintenance and future upgrades are sustainably funded, helping Raleigh maintain a robust and resilient transportation infrastructure network that supports long-term growth.

“Constructing projects that will support planned population growth in North Carolina is crucial,” says Patrick Norman, chief engineer at NCTA. “The Complete 540 project is an example of the type of innovative and efficient transportation solution needed to keep North Carolina moving forward.”

The Complete 540 project exemplifies how forward-thinking infrastructure can support safety, efficiency and environmental stewardship. Its turbine-style interchange and radial bridges across Juniper Branch stream enhance Raleigh’s transportation network, bolster the local economy and will shape communities for generations. As the Triangle area continues to grow, Complete 540 ensures that Raleigh’s roads are ready for a dynamic future.

Key Takeaways From Complete 540

• Community Engagement Is Essential. Early and consistent communication with the community is critical in addressing concerns and gathering valuable insights. Community feedback led to improvements in the design, including adjustments for noise reduction.

• Environmental Sustainability Needs to Be a Priority. Integrating sustainable practices from the outset helps mitigate environmental impacts and promotes long-term resilience. The stormwater management systems incorporated into this project serve as a model for environmentally responsible design.

• Innovation in Design Pays Off. The turbine-style interchange’s design, while more complex, has proven effective in reducing congestion and improving safety. The success of this design could pave the way for turbine-style interchanges across North Carolina’s highway network.

• Collaboration and Adaptability in Project Phasing Is Key. The successful completion of Complete 540 Phase 1 hinged on the collaborative efforts of multiple subcontractors, partners and stakeholders. This collaboration was crucial in coordinating various aspects of the design and construction processes, enabling the team to address challenges effectively and innovate solutions that met project goals and regulatory requirements.