Portage Bay Bridge Trail vs Surface Route tests will for minimum freeway width

Two possibilities for bridging pedestrians and bicycles between Capitol Hill & Montlake. Image: Montlaker via WSDOT

Two possibilities for ‘bridging’ pedestrians and bicycles between Capitol Hill & Montlake. Image: Montlaker via WSDOT

All has been quiet in 520 design news since WSDOT presented public comments to the Seattle City Council on November 26th. One issue getting a bit of attention is the Portage Bay Bridge width given the show of overwhelming public support during the public comment period for adding 14-foot trail. For years residents have lobbied for minimum freeway width to protect the natural environment of the 520 corridor. This year WSDOT published design drawings showing what the new 520 will look like from the bicycle and pedestrian point of view — and suddenly the debate changed.

Central Seattle Greenways supports using 520’s Portage Bay Bridge as a direct and easy-grade route up Capitol Hill. A recent blog post, Bridging the Topographic Fortress with a Trail, compares a Portage Bay Bridge Trail to alternative surface routes up and down the ‘fortress’ with the hard data of distance and grade. Really though, it’s a bit of a no-brainer: cycle up the Portage Bay Bridge (4.5% grade) — or — ride underneath 520, around Montlake Playfield, along the Boyer Ave arterial, then up a new trail through the Roanoke underbridge area that includes a dozen switchbacks to reach Delmar?

Image: WSDOT

Image: WSDOT

Flattening the steep grade between Seattle’s densest neighborhood (Capitol Hill), booming tech district (South Lake Union) and academic research center (UW) would go a long ways toward meeting the City’s goals for increasing bicycle use in the name of sustainability. And yet, the sustainability cause underpins the minimum bridge width demand as well. Or at least it did back when the 520 debate focused on numbers of vehicle lanes. So who bears the sustainability standard now? Minimal freeway footprint or 75 years of easy walking and biking up Capitol Hill?

Central Seattle Greenways’ Topographic Fortress offers ideas on having it both ways:

Even though the vast majority of community members and groups (including the Montlake Community Club and the Capitol Hill Community Council) support a Portage Bay Bridge Trail regardless of how the bridge is built, there is still interest in making the bridge as narrow as it can be without sacrificing its utility. Here are a few ideas that have been floating around:

  • Use steel rather than concrete for the bridge – this allows the bridge to have less visual bulk
  • Remove the planted median from the middle of the bridge
  • Reduce any unnecessary gusset space (the concrete webbing between lanes)
  • Decrease the lane width – the bridge is slated to be restricted to 45 mph, meaning that lanes can be an urban width rather than suburban freeway sized.
  • Finally it may be worth considering how hanging the Portage Bay Bridge Trail in different manners (underneath, partially offset, raised, etc) affects the light situation.

The first and last ideas likely have the most merit, as WSDOT claims to have done all it can to minimize the PBB width. While WSDOT should always be encouraged to sharpen its pencil, in the end, freeways are political products. And here are the democratic politics of the public comment period:

Support to include a 14-foot regional shared-use path on the Portage Bay Bridge. (Approximately 1,298 of 1,339 individual comments support this preference.)

So it seems the Seattle public is willing to add width to the bridge for the right reason — in this case, using your own two feet to walk or bike along 520.