Sunday, January 31, 2016

Marin County, California Bridges: NWPRR Corte Madera Creek Bridge

January 2016 (37.94332-122.51351) NWPRR Bridge 
There used to be several movable bridges in Marin County but only two remain. The Petaluma River Railroad Bridge is on the border with Sonoma County and it was covered in a 2014 blog. The Corte Madera Creek Bridge was made famous by Clint Eastwood who jumped off the trestle portion onto a school bus (without a stunt double) in the film 'Dirty Harry.'  The section Clint Eastwood jumped from (over Sir Francis Drake Blvd) was removed in 2003.

Terry Koglin in his book 'Movable Bridges' managed to provide data on every movable bridge in the U.S. He wrote that today's bridge was built in 1930. It includes an 80 ft long bascule span. It was owned by the Northwest Pacific Railroad but it's currently abandoned. The bascule span provided 10.5 ft of vertical clearance in the closed position but it has remained open for many years and is covered with rust.
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Marin County, California Bridges: NWPRR Corte Madera Creek Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Sunday, January 24, 2016

Marin County, California Bridges: Alexander Avenue Bridge across the Larkspur - Corte Madera Path

December 2015 (37.93001-122.53203) Alexander Avenue Bridge
The Alexander Avenue Bridge (27C0150) has a short pony arch main span and long slab approach spans. It was designed and built in 1925 by Larkspur city engineer John Oglesby. It originally crossed over the Northwestern Pacific Railroad, which was eventually turned into a bicycle and foot path.
The bridge was listed as a historic place in 1984 but it was so deteriorated and seismically unsafe that the city considered replacing it. Eventually it was rehabilitated and retrofitted by the Hanna Group in 2012 at a cost of $1.4 million (paid for with state and federal funds). Work was completed in 2014 by the Ghilotti Construction Co.

The bridge looks a little odd with brand new columns supporting an aged superstructure and with the tall columns and tall arches supporting such a short span. Also the steep approaches look a little funny. I guess all of these peculiarities make it into a unique and interesting bridge.
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Marin County, California Bridges: Alexander Avenue Bridge across the Larkspur - Corte Madera Path by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Sunday, January 17, 2016

Marin County, California Bridges: Marin County Tunnels

2016 Marin County Tunnels
Are tunnels a kind of bridge? Because of the hilly terrain there are quite a few tunnels in Marin County. The photo above shows the 2350 ft long Cronkhite (Bunker Road) Tunnel (27 0039). It was built in 1917 and carries traffic under US 101 to and from the Marin Headlands (the southern tip of Marin County). It's just wide enough for a single traffic lane so cars (but not bikes) have to wait 5 minutes for the light to turn green on each end of the tunnel.
The nearby Waldo Tunnels (27 0040L/R) are 1000 ft long and were built in 1937 and 1954.  Since they carry busy US 101, they consist of two parallel 4 lane tunnels to and from the Golden Gate Bridge (shown above).
Marin County is big on bicycles and so there are several bicycle routes for commuters.  I rode on the Cal Park Hill Pathway which shares a 1000 ft long tunnel with the Sonoma-Marin Area Rail Transit (SMART) Line. It includes a gate that closes the bike path at midnight (shown above). There are several similar 19th century railroad tunnels that are being renovated for new passenger rail lines and bike paths.
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Marin County, California Bridges: Marin County Tunnels by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Sunday, January 10, 2016

Marin County, California Bridges: The Richardson Bay Bridge


There aren't too many long bridges in Marin County. The Richardson Bay Bridge is a 873 ft long precast girder bridge (with a few box girder and T girder spans) that was built in 1957 and widened in 1973. It carries busy US-101 north of the Golden Gate Bridge through the affluent Mill Valley. Like a lot of other long bridges, the Richardson Bay Bridge has mostly flexible piers that alternate with occasional stiff lateral restraining piers. Despite or because of this kind of seismic design, the bridge suffered moderate damage during the 1989 Loma Pieta earthquake, but that didn't result in closure. After the earthquake, Caltrans provided a retrofit that consisted of infill walls to resist the lateral load.
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Marin County, California Bridges: The Richardson Bay Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Sunday, January 3, 2016

Marin County, California Bridges: The Golden Gate Bridge

December 2015 (37.827, -122.488) The Golden Gate Bridge
The other big bridge in Marin County is the Golden Gate, which connects San Francisco and Marin Counties. We last studied this bridge from my wife's Prius on August 6, 2014. Today's view is from the Marin Headlands, but unfortunately, Point Diablo is blocking our view of the north end of the bridge. Actually, there are really great views just north of the Point, but it was so crowded with tourists when we visited, that I couldn't find a place to park. However, we are planning to go back in a few weeks and hopefully I can take a photo of the entire bridge then.

Behind the Golden Gate Bridge is the City of San Francisco to the right, the San Francisco-Oakland Bay Bridge (the Bay Bridge) in the center, and the Oakland Hills on the left. We were lucky to have such a clear view, since the Golden Gate is often shrouded in fog.

Unlike the Bay Bridge, the Golden Gate Bridge suffered no damage during the 1989 Loma Prieta Earthquake. However, the epicenter of that earthquake was 100 km away. The bridge owner (The Golden Gate Bridge, Highway, and Transportation District) is currently completing a retrofit design of the main spans and construction will hopefully commence in 2017.
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Marin County, California Bridges: The Golden Gate Bridge by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.