Why Must We Replace the Historic Sellwood Bridge?

The common assumption that we must replace the Sellwood Bridge in the near future is surprising when it appears that rehabilitation might well extend its life and improve its utility for another 80 years or more. This historic 1925 structure is currently suffering from lack of maintenance and lack of respect. We can remedy both problems.

In November 2005, Multnomah County received the results of an analysis of the structural condition of the bridge, performed by David Evans and Associates. While this report comprehensively answers the questions posed by the County, it may have asked the wrong questions. What the County asked was: what can we do to extend the life of the bridge for 15 years and possibly upgrade the current weight restrictions, without closing it down?

However, the detailed results of this study appear to be fully consistent with a more hopeful view of the bridge's future.

Here is an alternative vision:

The role of the Sellwood bridge in the existing Metro and City of Portland transportation plans is to connect a two-lane arterial, Tacoma St. across the Willamette River to Macadam Ave. There is no reason to expand the bridge to 4 lanes, given that role. The question then becomes: What makes the most economical sense as a way to retain a two-lane traffic connection while improving the currently inadequate transit, bicycle, and pedestrian connections? Should we replace or rehab the bridge?

Here is an argument for rehabilitation: We can probably do it sooner, with a lower life-cycle cost and less disruption, and with results that function as well or better than a replacement bridge.

The David Evans report reveals that the fate of the bridge is a matter of choice. The four main steel truss spans, which cross the open water of the river, are in fine shape in terms of strength, although they are suffering from deteriorating paint and a leaking deck. The components that are slowly failing, and that need immediate attention, are the deck support system ("floor beams" and "stringers") and the approach spans. Contributing to this failure are lack of maintenance, although the two problems that appear most responsible are (1) the effect of large loads over time on concrete structures that were designed to economically meet the load requirements of 1925, and (2) an active landslide at the west end. Not surprisingly, among the most compromised components are two steel approach spans that were recycled from the 1894 predecessor of today's Burnside Bridge.

Interestingly, the David Evans report outlines several alternative approaches to restoring the structural integrity of the approaches and deck support system, and dealing with the landslide, that would cost only a fraction of the cost of replacing the bridge. As a result, these measures make economic sense when viewed from the standpoint of extending the bridge life for only 15 years. However, some of these fixes could potentially have a much longer life if combined with replacement of the seriously damaged west approach structure, and a maintenance program that stops the current deterioration.

In addition to the repairs described in the David Evans report, we should replace the deteriorated railings and deck. The roadway should be widened, and build a new deck for pedestrians and bicycles underneath the main deck of the bridge.

A below-deck bicycle/pedestrian facility supported by the lower chords of the trusses would have protection from rain and vehicle spray, and could provide an easy connection to the Springwater Trail. At the west-end, we would build this deck into the new approach structure that could also have bus pullouts, ramps and stairs providing access to a transit stop on the proposed Portland Streetcar line to Lake Oswego.

Something worth mentioning is the benefit that comes from replacing the complete deck. The current reinforced concrete deck lacks sufficient shear connections to the beams and stringers that support it. This means that the deck and support structure do not act as a "composite." By updating the deck design to modern practices, we may make it possible to increase the strength or reduce the weight of the deck so that the bridge ends up "better than new" with regard to its ability to carry buses and most semi-trailer combinations (40 tons).

There is one significant cost in this approach that does not appear on the bottom line. To replace the deck and the west approach, we would probably have to close the bridge for up to a year. Metro, ODOT, and PDOT need to do some traffic modeling to determine the effect of this closure, and what mitigating measures are possible. However, compared with the disruption involved in replacing the bridge, this seems bearable.

Provided Jan. 4, 2006 by Jim Howell, AORTA Strategic Planner. Comments are welcome at:

3325 NE 45th Avenue
Portland, OR 97213
jimhowell89@hotmail.com

Restoring the Sellwood Bridge for an additional 80-100 years of usable life could save tens of millions of dollars, and we could accomplish it many years sooner than replacing it.

A major reason for the popular assumption that bridge replacement is the only long-range solution is because restoration would close it for an extended period of time and thus create major regional traffic disruption. However, we could largely mitigate this disruption with public transportation.

I propose that a new east-west regional bus route and a temporary "bus ferry", operated during construction, could greatly reduce the amount of new traffic that would otherwise shift to the Ross Island Bridge due to this closure.

Here is the plan:

1. Establish an east-west cross-town frequent service bus route between Clackamas Town Center and Washington Square via SE Johnson Creek Blvd., SE Tacoma Street and SW Taylor's Ferry Road.

2. Provide a temporary ferry shuttle across the river for these buses as well as for pedestrians and bicycles.

3. Upgrade key north-south bus routes that cross this route to frequent service status in order to provide fast reliable service to more regional destinations. For example: #71, Parkrose - Clackamas Town Center; #70, Lloyd Center - Milwaukie; and #35, Portland City Center - Lake Oswego/Oregon City.

4. If possible, extend the Portland Streetcar line south to the ferry crossing in order to supplement the bus service on Macadam to the CBD.

This plan creates a grid of convenient transit service that would provide an attractive alternative to the automobile for Clackamas - Washington County commuters. This bus route crosses or connects to a third of TriMet's bus routes (33) and to one light rail line (I-205 Green Line, beginning in 2008).

Also, park and ride facilities at CTC and Washington Square, as well as small temporary sites along the route, could provide access to this new route for commuters without adequate local feeder bus service.

The project could include temporary ferryboat landings at the foot of SE Spokane Street and at the Powers Marine Park boat ramp off SW Macadam Avenue. The landings should be wide enough for two small boats capable of carrying a fully loaded 40-foot TriMet bus, plus walk-on passengers and bicycles.

Access to the east side landing would be straightforward, but the project would require bus actuated traffic signals at Macadam and at the railroad underpass to ensure safety and one way operation at the blind curve under the railroad track. (See attached photos).

The service should provide two boats to ensure no wait bus boardings and for a backup boat in case of mechanical or other type of breakdown. The boats could also transport emergency vehicles.

Provided Jan. 12, 2006 by Jim Howell, AORTA Strategic Planner. Comments are welcome at:

3325 NE 45th Avenue
Portland, OR 97213
jimhowell89@hotmail.com