HNTB Corporation

Project Location: Los Angeles, California

Category: Transportation + Infrastructure

Started: January 15, 2016

Completed: July 9, 2022

Project Team: 

HNTB was the architect of record and engineer of record. The design team included Michael Maltzan Architecture and Dissing+Weitling, architecture; Hargreaves Jones, landscape architecture; AC Martin, urban planning; Light Projects Limited, viaduct lighting; EMI, geotechnical engineer of record; MGE, viaduct independent check; Pac Rim Engineering, structural design support; V&A, traffic; NCG and Armeni Consulting Services, construction cost estimating; Pacifica Services, environmental permits service; Glenn Kaino, art; Construction Technology Laboratory, mass concrete assessment; and West Wind Laboratories, wind consultant. Construction was led by Skanska USA/Stacy and Witbeck, the construction manager/general contractor. The construction management team included T.Y. Lin International Group, consultant; Psomas, consultant; WJE, concrete repair assessment specialist; Alta Vista, material/fabrication inspection; GPA, SWPPP and environmental compliance; EarthSpectives, CIDH pile compliance; KKCS, schedule review support; ZTC, source inspection; Lenax, change order analysis and IDC, construction engineering.

Project Summary: The largest, most complex bridge project in Los Angeles history, the Sixth Street Viaduct Replacement Project sets a new threshold for seismic safety and expands the utility of urban bridges. The new viaduct opened to traffic July 10, 2022, replacing a beloved double steel arch landmark with 10 pairs of sculptural arches unspooling 3,060 feet across an industrial lowland. The largest, most complex bridge project in L.A. history, the structure advances the field of seismic bridge engineering and the engineering profession with a series of innovations. Designed to remain undamaged and operational after a seismic event with a 1,000-year return period, the viaduct is believed to be the world’s longest, seismically isolated concrete tied arch bridge. It features the first US application of seismic isolators within the verticality of a bent, the world’s first use of triple-pendulum friction bearings modified to stiffen after a predetermined displacement, the first US bridge to use post-tension couplers and Caltrans’ first use of grade 80-ksi concrete. 

Further, the viaduct is designed to serve multiple purposes: 

  • Ensure greater public safety, preserve mobility and encourage multimodal travel
  • Instill civic pride and sense of place as a world-class Los Angeles icon
  • Increase transportation equity in the community of Boyle Heights
  • Unify Boyle Heights with the Arts District of Los Angeles
  • Provide safe, direct access to a future 12-acre public park below the viaduct
  • Instantly transform into a civic venue 
  • Serve L.A. for the next 100 years with minimal maintenance

The new Sixth Street Viaduct will provide a cinematic backdrop for movies and everyday life for generations to come. In a city of stars, it is a star in its own right. And much like the city itself, there is not another like it anywhere on earth.