Regional Boards > Pacific Southwest

CA 47 and the Vincent Thomas Bridge

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Occidental Tourist:
Or adding a second deck, which would address the lack of shoulders, and not require closure of the bridge once repairs are made to the original deck.

skluth:

--- Quote from: Occidental Tourist on May 22, 2023, 01:17:42 PM ---Or adding a second deck, which would address the lack of shoulders, and not require closure of the bridge once repairs are made to the original deck.

--- End quote ---

I like the idea. Could a second deck be retrofitted to the bridge? It would add a lot of weight and change the air flow around the bridge. Just curious. I honestly have no idea of the engineering involved.

Plutonic Panda:
I like that idea as well as I love the look of the current bridge and then you hit the new bridge and it’s a cool contrast.

roadfro:

--- Quote from: skluth on May 22, 2023, 06:32:17 PM ---
--- Quote from: Occidental Tourist on May 22, 2023, 01:17:42 PM ---Or adding a second deck, which would address the lack of shoulders, and not require closure of the bridge once repairs are made to the original deck.

--- End quote ---

I like the idea. Could a second deck be retrofitted to the bridge? It would add a lot of weight and change the air flow around the bridge. Just curious. I honestly have no idea of the engineering involved.

--- End quote ---

You typically can't just add a second deck on to a bridge. Bridges are designed and engineered to address a variety of design assumptions (which include but aren't limited to dead load aka weight of the bridge itself, traffic loads, future pavement overlays, etc.) and safety criteria (e.g. earthquake loading). If a bridge wasn't engineered for a second deck in the first place, a lot of these safety and design criteria would have to be reevaluated and the bridge would likely need serious retrofitting to accommodate a second deck–such that it would likely be easier and potentially even cost less to just build a new bridge outright.

Occidental Tourist:
I know that the bridge authority contemplated adding a second deck to the Golden Gate Bridge for awhile to accommodate more traffic, and actually commissioned a study in the 60’s that concluded it was feasible with only a few engineering changes to the existing structure. 

I believe the idea was to add the second deck below the Golden Gate’s existing one.  I’m not sure that would be duplicable with the Vincent Thomas Bridge given the current height of the existing deck and the shipping traffic that passes underneath.  My recollection is that the Vincent Thomas is about 50’ closer to the water than the Golden Gate, owing to the Golden Gate’s approaches being elevated on bluffs and the Vincent Thomas’s east approach being essentially at sea level.  Given the clearance issue, I have no idea of the differences in engineering concepts of building a second deck on top of the existing roadway deck as opposed to below it like was contemplated for the Golden Gate. And as is pointed out above, even though they are both suspension bridges, the design and materials of the Golden Gate could be different enough from the Vincent Thomas so that while the Golden Gate could safely accommodate a second deck, the Vincent Thomas could not.

So I agree that in all likelihood it’s a pipe dream. Actually, even if it could be accomplished as an engineering feat, it’s still a pipe dream in this day and age of shifted transportation priorities.

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