Sunday, November 16, 2014

Denver Ave. Bridge

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The next Columbia Slough bridge on our little tour is the one that carries N. Denver Ave. over the slough. Like the MLK and N. Portland Road bridges, this is an ODOT-owned bridge, since this stretch of Denver Ave. doubles as a chunk of highway OR 99W. At one time, 99W (a.k.a. the "West Side Highway") continued through downtown Portland, from SW Barbur to Front Avenue, then along Harbor Drive to the Steel Bridge, then up Interstate Avenue to Kenton, where it jogged over to become Denver Avenue, and then headed across the Columbia Slough north to the Interstate Bridge. Most of that stretch is no longer a state highway, but the stretch of Denver Ave. north of Argyle St. still is for some reason.

The Portland stretch of 99W was a late addition to the state highway system. At the time the Interstate Bridge went in, there was a great deal of infighting about which street would be the main approach to the bridge: Union Avenue (now MLK) or Vancouver Avenue, which Union Ave. finally won after a few years of rival booster clubs duking it out. Interstate (then known as Patton Avenue) wasn't in the running, because a steep bluff at the south end meant it didn't actually connect directly to downtown back then. It was a major local street, and was platted out as a wide street in case it became a major arterial later (which was a huge help when the MAX Yellow Line went in), but in 1916 it dead ended somewhere around today's Overlook Park. So a small wooden bridge was built, giving local traffic access to the Interstate Bridge.

A decade later, a major roadcut project finally connected Patton Avenue to the Steel Bridge and downtown Portland, and the widened street was rededicated as Interstate Avenue in September 1928, though a lot of references I've seen give 1929 as the actual project completion date. The bridge over the Columbia Slough was reconstructed at that point to handle the additional traffic. The Oregonian's "Year in Review" article on Jan 1. 1930 portrayed the Interstate Ave. project as one of the year's major news stories. A 1947 aerial photo shows the bridge here, along with an area of commercial development along the Kenton stretch of Interstate, but you can see that parts of the surrounding area were still semi-rural even then. A couple of interesting Cafe Unknown posts have more about the history of Interstate Avenue, with all its ups and downs, from potholed neighborhood street to neon wonderland, to blighted backwater after I-5 opened, and now to a rapidly gentrifying neighborhood with its own MAX line.

ODOT's 2012 bridge condition report says the slough bridge dates to 1916, while the adjacent viaduct over Columbia Blvd and the Union Pacific railroad is circa 1929. So it's possible there was a surface level intersection and railroad crossing here until the bridge upgrade project, in which case the original slough bridge was probably lower than the current one. That's my guess, anyway.

The 2013 state historic bridge inventory describes the bridge and viaduct:

In the late 1920s, increased traffic on the West Side Highway led to a major revision in how the highway approached the Interstate Bridge, then the only Portland area crossing into Washington State. Prior to this redesignation, the West Side Highway ended at downtown Portland, with only the Pacific Highway continuing over the bridge. These new bridges were designed to match those on the Pacific Highway, and continued to be a major part of the approach until the construction of I-5. They both feature a unique baluster railing, which is now mostly hidden behind protective wooden paneling.

Unfortunately I don't think you can see the unique bridge railing very well in any of these photos. The inventory PDF has a better photo, showing it really doesn't look all that different from other ODOT bridges of that era. The inventory goes on to mention that the slough bridge consists of "Three 78-ft steel girder and floorbeam system spans with reinforced concrete deck girder approach spans", while the viaduct is "Thirteen 71-ft reinforced concrete girder and floorbeam system spans with curved haunches.. ODOT researched the history of the Denver Ave viaduct over the railroad for the MAX Yellow Line project. The study determined it was ineligible for the National Register of Historic Places, and mentioned the slough bridge as similarly utilitarian & ineligible. The city's historical research for the Vancouver Ave. bridge replacement also mentions the Denver Ave. bridge briefly, but doesn't have much to say about it.

No discussion I've seen of the bridge mentions who designed it, and they usually do if a bridge is by someone well-known or historically important. The Union Ave./MLK, N. Portland Road, BNSF railroad, and (original) Vancouver Ave. bridges turned out to be minor designs by rather famous bridge engineers, but as far as I can tell that's not the case here. Perhaps as a result, it doesn't have a BridgeHunter or Structurae page of its own, but it does at least have an entry. That page tells us the bridge has an ODOT sufficiency rating of 51.7 out of 100 (as of April 2013), and it's described as being in "fair" condition and "functionally obsolete". It received an underwater inspection in 2011, which noted that the underwater portion of the bridge pilings are not entirely steel and concrete, which is a little surprising: "The part of this structure across the slough consists of 3 steel girder spans of 78 ft. each. Each pier is supported on two concrete columns with a webwall in between, that are supported by two individual concrete footings founded on untreated timber piling."

An upcoming ODOT project will redesign the intersection of Denver Ave. & Schmeer Road, directly north of the bridge. At present the north end of the bridge crosses an underpass that routes southbound traffic onto Schmeer Rd. The redesign will move the intersection north, and turn the underpass into a stretch of the Columbia Slough Trail instead. In Spring 2015 they'll also start work on the bridge and viaduct, resurfacing them and replacing the current bridge railings and adding crash barriers. Schematics of the new design indicate there will be a crash barrier separating the sidewalk from street traffic, and the redesigned bridge will include separate bike lanes, which it doesn't currently have. It will still only have a sidewalk on one side of the bridge, I suppose because extending the bridge out to add one on the other side would be too expensive. Still, it seems like a positive step, in an area that's only going to have more bike and pedestrian traffic as the Columbia Slough Trail keeps being extended.

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