She said that new jobs and housing growth in San Francisco and the East Bay will translate into more people commuting in and out of San Francisco.
"All new workers will not be living in the city," Dennis-Phillips said. "We have to find a way to get them here."
With 8,000 new homes and hundreds of thousands of square feet of retail space expected to be built on Treasure Island in the coming decades, she said there will be even more demand to get people into the city via car, public transit, bicycle, ferry or otherwise.
More people coming into and out of San Francisco during peak commute hours in the morning and evening may lead to the Bay Bridge being unable to handle the heavier loads, said Anthony Bruzzone from Bay Area-based planning firm Arup.
The workforce in San Francisco, according to Bruzzone, consists of 40% who live in the city, 40% who come in from the East Bay, about 12% from the Peninsula and the remaining 8% from Marin County and the North Bay.
If that geographic breakdown continues into the coming decades, the capacity to carry people across the Bay will be strained, he said.
There are 190,000 new jobs expected in the city by the year 2040, which is a 30% increase from the current total, he said.
He said there are about 75,000 trips made into San Francisco on the Bay Bridge per day, with about half of those trips made during the morning commute.
By 2035, the capacity of the bridge -- and other transbay options such as BART -- is expected to exceed its limit, especially since there hasn't been added capacity to the "Bay corridor" since BART opened in 1974, Bruzzone said.
Before that, the Bay Bridge's conversion into a two-deck bridge in 1963 was the last time more people were able to get across the water.
"We've been living off the investments of our grandparents," Bruzzone said.
Bruzzone said a redesign concept to consider on the Bay Bridge in the coming years is a "contraflow configuration" which would allow certain lanes of traffic on the bridge to switch directions based on need and crowding.
This proposed system would purportedly help alleviate increasing congestion at the toll plaza from more and more cars that will inevitably be driving on the bridge once BART trains become too crowded, he said.
"At some point we run out of ways to get people in and out of town," Bruzzone said.
With a congested toll plaza, the highway system starts to break down as well, with cars backing onto Oakland freeways, he said.
Ridership levels have been steady on the Bay Bridge in the past 20 years, while BART has carried increasing numbers of riders.
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