Capitol Hill Seattle Blog recently covered architect Christopher Patano’s plan to put a “lid” on I-5 through a two mile segment alongside First Hill and Capitol Hill to create a linear park. It’s an exciting idea. Obviously it would be very expensive and require a huge political lift. But let’s discuss its merits. I’ve covered the damage freeway construction did to urban neighborhoods; this is one way to mitigate that damage without sacrificing highway capacity.
Scott Bonjukian covered this idea last year on his blog, conducted graduate research on an I-5 cap, and is planning a reveal more of his findings in an imminent blog post. His 2014 redux proposal focused on a 9.6 acre expansion of the existing Freeway Park between Pike Street and Seneca Street. He projected a $200 million price tag for this expansion. Patano insists on deflecting the question of cost for now, but Bonjukian had a longer option that went 2.5 miles from Galer Street all the way to Yesler Way, and he estimated a freeway cap that length would cost 2 billion dollars.
That hefty price tag could be partially—perhaps even mostly—offset by selling off some of the land parcels created over the freeway trench. Bonjukian estimated that the land created in those choice neighborhoods could be worth roughly $18.1 million per acre. Meanwhile the cost of the freeway cap is estimated at $20 million per acre, based on similar projects in Dallas, Philadelphia, and the Freeway Park project in Seattle.
If land values continuing shooting up, one could see land values surpassing the cost of creating that land with a freeway cap. Of course, some acreage would have to be set aside for cross streets and to reserve space in the middle for the parkway with a bike and pedestrian trail.
There is also the caveat there is developers would be hindered in how high they could build and in digging parking garages over the freeway due to the obvious engineering limitations. That would likely lower the land value. However, even low rise parcels could have very high value. Plus, the lid could be engineered to support mid-rise buildings; it just have to be further reinforced, which is expensive, but the increased costs could be covered by a developer wanting the extra height.
Moreover, the freeway cap could present a unique opportunity for the city to guide positive urban design in a way it rarely has the power to do. Instead of lamenting limited parking opportunities, the city would create a car-light, mixed-income zone with fantastic access to the newly created bicycle and pedestrian trail, not to mention frequent transit. I expect further cost savings could be realized by integrating foundation work into the freeway cap construction so that wood apartment buildings could go up quickly. Not having to dig parking ramps saves time and money. The apartments could be targeted at low and middle income tenants without cars and looking to take advantage of the new bike trail and great pedestrian access to downtown and Capitol Hill.
The project could be done in sections. However, once the low hanging fruit are completed nearer downtown (where I-5 is in a trench), a northward expansion would require more significant engineering and probably a lengthy closure to construct a more complicated cap, such as encasing the freeway in a seven-story structure like in the rendering. It appears apartment or hotel units are built right into the structure, which might work but doesn’t exactly make for very enticing real estate.
Patano’s vision for the northern half of the linear park is reminiscent of the much ballyhooed High Line in New York City that it seems every city now wants to copy (and which New York copied from Paris’ Plantee Promenade). Park space several stories up in the sky is a nice novelty but it’s hardly central to good urban design. High Line replicas run the risk of being exorbitantly expensive, underutilized flops. The High Line works well in New York because the surrounding neighborhoods are quite dense and, to be believe the boosters, the park catalyzed redevelopment that wouldn’t have otherwise have happened in the up-and-coming Chelsea neighborhood of Manhattan. The elevated park also draws a large number of tourists.
If your city doesn’t have redevelopment opportunities or a serious shortage of park space and tourist attractions near its planned elevated park then it might just be a vanity project. Unfortunately spending billions of dollars to build a High Line-like park on top of I-5 between East Lake and Capitol Hill might fall into that category. The downtown section of Patano’s plan seem more likely to have enough benefits to outweigh the costs. Capping the freeway downtown would provide a marked improvement to the public realm in this neglected area of the city and hopefully allow additional blocks to be developed to relieve some of the housing pressure in Seattle.