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Why does the Bay Area have so many cloverleafs?

Started by kernals12, October 25, 2020, 10:08:19 AM

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heynow415

Quote from: TheStranger on October 30, 2020, 11:11:46 AM
Quote from: kkt on October 29, 2020, 11:01:14 PM
US 101 - CA 92 was one terrible cloverleaf that's been made much better.  Much of the work was done in the early 1980s, if I remember right.


Looking at HistoricAerials, the work to upgrade that interchange to add the two flyovers (SB 101 to EB 92, NB 101 to WB 92) occurred sometime between 1984 and 1988.  There are stubs for flyovers that were never built (EB 92 to NB 101 and WB 92 to SB 101) during that project.

That interchange seemed to be another one that was partially constructed on the assumption of future improvements occurring (which fortunately did for the most part).  I remember in the late 70's/early 80's coming back from SFO to the east bay on 92 the s/b 101 to e/b 92 cloverleaf was constructed on wooden pilings, like a fishing pier or railroad trestle - haven't seen that one anywhere else.  The 92 mainline overpass over 101 was built in the typical early 70's design and this funky cloverleaf tied into it but, perhaps like the infamous "Stonehenge" 101/680/280 interchange that sat unfinished for many years, they didn't have the funds to complete it so that was the quick fix.  It was finally replaced with a flyover when the rest of 92 was improved in that area, including bypassing that solo signal at Norfolk St. 


sparker

#51
The US 101/CA 92 interchange was completed and open to traffic by December 1988.  I was at the Stereophile magazine audio show held at the now-gone Dunfey Hotel facing the northwest quadrant of that interchange in late April 1989; they were just doing the interchange landscaping (pretty much just sowing grass) at that time.  The original cloverleaf was simply a street interchange expanded into a rudimentary freeway-to-freeway facility; the CA 92 overpass wasn't even divided until the freeway east through Foster City to the bridge landing was widened in 1973-74.   

stevashe

Quote from: CtrlAltDel on October 30, 2020, 08:23:04 PM

I admit I'm not an expert on this, but I don't see how the I-880/US-101 interchange could affect the operations of the airport in any way. Assuming that the interchange is the red circle and the runways are the green lines, and I just can't see how a plane could swoop around from that interchange to line up with either of those two runways.



It may seem silly, but the FAA does mandate maximum structure heights on all sides of a runway, though they are much less strict on the sides than off the ends of course. As I understand it, the reason for this is for visibility when approaching at an angle as well as preventing interference with instruments.

That being said, I know for a fact that you can fit flyover ramps at 880/101 there within the height limits because a couple students at my university designed a stack interchange replacement for their senior project. And the comments others have made about cost and Right of Way/eminent domain are right on the mark, they did indeed find that significant property would be needed and the cost would thus be prohibitive. (Not to mention very limited merge areas due to close spaced interchanges all around.)

kkt

What a good project!  Was that at a Bay Area college?

stevashe

Quote from: kkt on November 15, 2020, 09:08:25 AM
What a good project!  Was that at a Bay Area college?

Yup! Santa Clara University, which is just in the bottom left of the aerial CtrlAltDel posted :P



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