Double-Deck The 405?

[cpzilliacus]

KNX-1070:  Double-Deck The 405? MTA To Hear From Public On Sepulveda Pass

When it comes to relieving traffic along one of the nation's busiest stretches of freeway, the Metropolitan Transit Authority appears ready to consider all possibilities.

The MTA will hold a public meeting on Tuesday to hear input on ideas to ease congestion in the Sepulveda Pass, with options including adding a second deck to the 405 Freeway and building a tunnel through the Santa Monica Mountains.

While the proposals may sound far-fetched, Kymberleigh Richards with the Metro San Fernando Valley Service Council told KNX 1070 NEWSRADIO there may be a precedent for "double-decking"  — along with a whole host of concerns.

[Road Hog]

That worked well in Oakland in 1989.

[TheStranger]

That worked well in Oakland in 1989.

This would probably be more like the current express lane setup on the Harbor Freeway though, as opposed to the design used on the pre-1989 Cypress Freeway.

[myosh_tino]

That worked well in Oakland in 1989.

This would probably be more like the current express lane setup on the Harbor Freeway though, as opposed to the design used on the pre-1989 Cypress Freeway.

While construction practices have improved over the past 50 years, I still think double-deck freeways in earthquake country are a bad idea.

[KEK Inc.]

The engineering issues with the Cypress Viaduct is that its concrete rebar didn't allow for any flexibility.  When you account flexibility to load-bearing supports, the structure can withstand more periodic motion. 

CalTrans has learned.  They modernized I-280 in the SF right after Loma Prieta.



Now, the Alaskan Way Viaduct in Seattle...

[myosh_tino]

The engineering issues with the Cypress Viaduct is that its concrete rebar didn't allow for any flexibility.  When you account flexibility to load-bearing supports, the structure can withstand more periodic motion. 

It also didn't help that the support columns were tapered like a high-heeled shoe...

CalTrans has learned.  They modernized I-280 in the SF right after Loma Prieta.

I don't think "modernized" is the right term... retrofit is a better one.  All that was done to the I-280 support columns was to wrap them is steel and re-bar.

[KEK Inc.]

The engineering issues with the Cypress Viaduct is that its concrete rebar didn't allow for any flexibility.  When you account flexibility to load-bearing supports, the structure can withstand more periodic motion. 

It also didn't help that the support columns were tapered like a high-heeled shoe...

CalTrans has learned.  They modernized I-280 in the SF right after Loma Prieta.

I don't think "modernized" is the right term... retrofit is a better one.  All that was done to the I-280 support columns was to wrap them is steel and re-bar.

Yeah, retrofit is a better word for what I meant. 

Damn, I think the Alaskan Way Viaduct has a similar design on its structure.  Fortunately, Seattle isn't as prone to Loma-Preita style earthquakes as Oakland is, but even a 6.0 could bring bad news to many Seattle roads. 

[triplemultiplex]

Damn, I think the Alaskan Way Viaduct has a similar design on its structure.  Fortunately, Seattle isn't as prone to Loma-Preita style earthquakes as Oakland is, but even a 6.0 could bring bad news to many Seattle roads. 

Seattle, Portland and Vancouver have huge a subduction zone off the coast, so they will eventually have the largest type of earthquake that is tectonically possible.  It's not if they'll have a 9.0 up there, it's when.  Their minor quakes are less destructive because they're deeper, but once that subduction fault pops again, hold on to your butts.

[LA_MetroMan]

Good Luck getting past Mr. Silver and his Encino Homeowners Group. They've held up all sensible additions to the freeway network (101/405) through their neighborhood.