When Doyle Drive became structurally and seismically deficient, the California Department of Transportation and the San Francisco County Transportation Authority led the effort to replace a 1.6-mile segment of Route 101 with a new Presidio Parkway that would be safer for traffic and serve as a regional gateway. HNTB served as lead designer and provided construction design services for Phase II of California’s first public-private partnership (P3) alternative delivery project.

The design included a high viaduct, completing the US 1 interchange, and designing three new cut-and-cover tunnels, four low viaduct structures, and a new diamond interchange. By concealing large sections of the highway in tunnels and tucking the tunnels into the area’s natural contours, passengers have unobstructed sightlines of the bay.

With its combination of bay muds and shallow aquifers, the unstable soil was prone to liquefication and incapable of supporting the parkway’s viaducts, tunnels and retaining walls. The team used cemented deep soil mixing to strengthen the ground, which creates columnar grids of soil and grout strong enough to support the structural loads.

Thanks to the innovation used in designing infrastructure for high-seismicity areas, the Presidio Parkway can withstand a magnitude 8.3 earthquake, the maximum consideration for the region.

Location: San Francisco, CA

Client: California Department of Transportation, San Francisco County Transportation Authority

Awards: Roads and Bridges - Top 10 Bridges; ASCE Region 9 Outstanding Structural Engineering Project of the Year; California Transportation Foundation Project of the Year; National Council for Public-Private Partnership (NCPPP) - Infrastructure Project Award

Services: lead design, construction design, design build