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Nashville Roundabout, Part of Gateway Boulevard Final Design

 

Nashville Roundabout
Gateway Boulevard was constructed as an urban “zipper,” a street that is designed to join together downtown Nashville’s urban fabric using wide sidewalks, ample medians and plantings, and travel lanes fringed with on-street parking. The roundabout functions as the centerpiece of the revitalization of the SoBro area and as an iconic gateway into downtown Nashville, involving two federal highways (US 41 and US 31), which by law had to remain open during construction of Gateway Boulevard.

Technical issues evaluated included traffic operations analysis, which was crucial to the development of functional designs for the proposed alternatives, especially the roundabout intersection. As part of the analysis, WSP USA developed Synchro traffic analysis models to analyze intersection capacity and levels of service and recommend mitigation and intersection geometric concepts, and prepared a two-lane roundabout concept and geometric detail that was analyzed using VISSIM and AASIDRA models.

The design incorporates the latest standards of practice to accommodate high vehicle and pedestrian volumes, low design speeds, truck turning movements, challenging topography, drainage and utility issues. Due to the complexity of the intersection, careful consideration of the signing and striping plan was necessary to reduce motorist confusion and encourage entry into the roundabout in the appropriate lane. The roundabout design incorporates channelization to maximize throughput and minimize the footprint in this area. Sidewalks, splitter islands and crosswalks were designed to meet Americans with Disabilities Act (ADA) ramp requirements.

The scope of work included right-of-way and final plans and construction documents and included extensive coordination with Tennessee Department of Transportation, Federal Highway Administration (FHWA), Tennessee Department of Environment and Conservation, other state and local agencies and utilities as well as the Music City convention center design and construction teams. The work also included coordinating with the construction of the adjacent Metro Convention Center, 22 utilities, subcontractors, and other stakeholders.

Roundabout features include:

 

  • All approaches to the dual lane roundabout have multiple entry lanes

  • Roadway skews required a larger-than-average inscribed diameter (230 feet) to provide adequate deflection and speed controls

  • Stakeholders desired an “iconic” circular sidewalk concentric to the roundabout, requiring careful planning of the splitter islands and crosswalk locations.

  • Sustainable features include LED pedestrian lighting, pervious pavement, and diversion of stormwater runoff to provide landscape irrigation.


The project was completed in compliance with the Manual of Uniform Traffic Control Devices and the Tennessee Department of Transportation.

The Nashville Roundabout won the American Council of Engineering Companies' 2013 Award for Engineering Excellence.