Bay Area Rapid Transit Warm Springs Extension

HNTB-designed transit bridge built to survive severe displacement

•    Bridge straddling fault is first for United States
•    Designed to survive displacement from 7.25 earthquake
•    Trains can resume operation within reasonable time

HNTB was the lead designer for a 5.4-mile design-build project that extends the Bay Area Rapid Transit’s rail line from Fremont Station to a new Warm Springs Station. The project’s Walnut Avenue Bridge is a first for the United States. It straddles the Hayward Fault and is designed to survive severe fault displacement from a magnitude 7.25 earthquake, allowing trains to resume operation within a reasonable time.

HNTB used computer modeling software to analyze the effects different seismic events would have on a bridge in the fault zone. After collaborating with BART, the contractor and the University of California, Berkeley, HNTB produced a cutting-edge design: a post-tension, concrete through-girder railroad bridge supported on short seat-type spread footing abutments on top of mechanically stabilized earth walls. The MSE wall supporting southern abutment rests on a load transfer slab, protecting the MSE walls and abutment from extreme differential ground movements.