Engineers Zero In on Design for Bike Path on Bay Bridge Western Span

Transportation officials are narrowing the final designs for a bike and pedestrian path on the western span of the Bay Bridge, something bike advocates have been dreaming about for decades.

But it could still be another decade before the 2.9-mile structure from Yerba Buena Island to San Francisco is funded and built, according to the Bay Area Toll Authority.

"Even two years ago, I wouldn't have thought we'd be where we are," said Renee Rivera, executive director of Bike East Bay. "It seems crazy to be excited about something that's not going to happen for 10 years, but the thing is we've been working on this for maybe 25 years already."

The impetus to build a western path comes from a desire to make it possible to ride all the way from Oakland to San Francisco. The new eastern span's biking and walking path currently stops short of Yerba Buena Island because of a long series of construction delays.

At a recent community meeting that drew more than 100 people, representatives of engineering and design firm Arup presented several designs. They include a path that would be suspended above the current traffic lanes and options for building paths hung on the north or south sides of the western span.

One big question is where the path should touch down in San Francisco. Engineers have narrowed those alternatives from 19 to six, including Essex Street, the Embarcadero or a Caltrans paint yard.

Rivera says she favors the Essex Street landing, partly because it is simpler, would cost less and brings commute cyclists directly into downtown, where most would likely be headed.

"I think Essex is the easiest, the most elegant and the most functional of the options," she said.

Estimates are that as many as 10,000 bicyclists would use the path daily (1,300 during peak hours), more than cycle daily on the Golden Gate Bridge, said Rich Coffin, principal engineer on the project for Arup. That number also considers an additional 20,000 residents projected to be living on Treasure Island.

A biking and walking structure on the western span presents a number of engineering challenges. Rafael Manzanarez, another Arup engineer working on the project, outlined some of them, according to this account from Richmond Confidential's Sam Omar Hill:

Attaching the main span to the Bay Bridge is the “biggest challenge,” Manzanarez said, because it’s not easy to attach new steel to old steel. Old steel gets brittle. It can’t be welded. The old bridge must be partially taken apart and the new parts must be integrated using bolts and plates to replace existing rivets.

“It’s just surgical work,” Manzanarez said with a laugh. “It’s getting into somebody’s body.”

There’s also the issue of sinkage. Adding new weight will cause the bridge to be six to eight inches lower, potentially endangering very tall ships and angering the Coast Guard. To solve this problem, Manzanarez said that the suspension wires could be tightened, raising the roadway back up six to eight inches.

Another big question is how to get the path across Yerba Buena Island. The options include a bike and walking path that would be suspended from the ceiling of the Yerba Buena Tunnel, providing a direct connection to the west span. Less costly options include building paths above or below Hillcrest Road, which winds around steep terrain on the south side of the island.

In San Francisco, the project would also feature "dual high-capacity and high-speed elevators" on the Embarcadero to quickly move people on and off the path. One option being considered would be to have the elevators open first, in lieu of a ramp touchdown, which could be built later.

Engineers hope to come up with four alternative designs and present cost estimates at a meeting planned for September, and then narrow them down to two options.

Part of the current design effort is to find a design that can be built for under $300 million -- far less than early estimates for the project. Bay Area Toll Authority officials said they are considering raising bridge tolls to cover the cost as part of a regional measure that would also fund a number of other transportation projects.

"We need to find a design that's affordable, and if we're going to go higher than that, then we need to figure out what that means," said Randy Rentschler, a spokesman for the toll authority.

Rentschler said he's cautiously optimistic about the future of a west span path, but added that "the ambitions of a bike path have to come through a comparative reality against all the other things that the citizens of the Bay Area want to have in that corridor, and in general."

Rivera is hoping that things will progress so construction -- which would take three to five years -- could start as early as 2019.

"We hoped we would come to this day where the political will is lined up," said Rivera. "This project feels like it has so much momentum. It feels like there's no going back."