Capping Vine Redux

Remember this post? Remember this picture?

Well, with the new Mormon apartment building, I thought I'd bring it back to life, and put more meat on them bones.

Here we see, in purple, the major developments near Vine between Broad and Logan Square: the Mormon Temple, their Meetinghouse, the new apartment building at 1601 Vine, the Provence, and the apartment buildings buttressing Broad and Callowhill. Under it, we see the old cap plan. Intermingled with these, we also have some additions: several mews structures to take advantage of the increased desirability, and a small park over the exit ramp at 15th and Vine.

In the cloverleaf, we build a new "Sydenham Mall" (Sydenham being the name of the interstitial street between 15th and 16th); flanking it, large buildings fronting each of the four corners. They would share mechanicals and loading docks in the cloverleaf curve; inasmuch as possible, they would cover the interchange. Retail fronting Sydenham would lead up to the Provence*; retail fronting 16th would help urbanize that street further; flex space would front 15th.

Between all of these additions, the Vine Street Expressway would be completely hidden from 12th to 21st-ish. It would become the perfect example of the proper placement of heavy transportation infrastructure in the city--grade-separated, out of mind.**
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*If the Provence is built. As you may recall, I noted in A Provincial "Provence" that turning the cloverleaf green is, in fact, the worst possible for it.
**Remember, in Death and Life, Jane Jacobs noted that the most marginal uses--and hence the worst land values--were (in her time) usually located next to railroad tracks; this can be expanded to include Interstates today, for various reasons. Both are heavy infrastructure. The fact of the matter is that heavy transportation infrastructure, while indubitably necessary for the city to function properly (to get imports in and exports out à la her economies trilogy), also have a depressing effect on adjacent land. My extension of this point is--one of planning's major goals should thus be minimization of this effect by making heavy transpo infra "invisible" from an urban-dynamics point of view.

Expressway Caps

Columbus has an interesting expressway cap on High Street. Check it out.

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High Street cap from the sky

While the Tribune blog bloviated over its similarities to Columbus' former (lost) Union Station--alas, poor Union Station--for planners that's not the key takeaway: instead, the key takeaway is that it is very much possible (though not cheap) to build light freeway caps. (This one cost just under $10 million.) The other takeaway is that a freeway cap need not be just for recreational land use. Boston, I'm looking at you.

High Street crossing the cap. Look, ma! No expressway!

Instead of a fully underground, Big Dig-type scenario, the Columbus example gives us some counter-ideas. When it is necessary--for whatever reason*--to run a sunken expressway through an urban area (usually due to the inertia of one already existing), it would be far better--and cheaper--to mitigate the impact by deploying these cap structures--or more accurately, in most cases, salable cap slabs.

Such as these slabs in this unfinished development.

In either case, the interventions are different than the major interventions that usually involve acquiring an Interstate's air rights: in those cases, space for full cores needs to be found, and anchored on solid ground. In this case, however, the structures are diminutive enough--single story commercial, townhouses, walkups, or possibly retail with a townhouse or walkups atop--that they need only basic infrastructural hookups (electricity, plumbing, and fiber)** that can be routed through the cap--no need for such expenses as elevators. Additionally, well-known green roof installation techniques can be used to add grass to whatever open space local zoning laws require in the rear of the property, please; a low wall (about 10 ft.) separates the livable space from the transportation space. With caps another possibility may be to provide a cap base along an entire city block that e.g. garden apartments can be built on. Unlike the cap concept, however, this concept would become a full tunnel and necessitate ventilation equipment somewhere on site.

Click it to see it in all its glory!

This is the first of the two concepts I whipped up for this post. The Vine Street Expressway is a sunken highway dividing--despite the crossing frequency--Center City from North Philly. The sunken section runs from 10th St. to 22nd St., or 12 blocks (with 13 spans). It additionally passes by Logan Square, a pretty dismal City Beautiful mess anchored by an excessively autocentric traffic circle. This model proposes closing open caps currently situated between 18th and 21st Sts, and providing for small commercial or multipurpose salable slab space alongside each of the other bridges. As time goes on, cap additions between these caps can completely conceal the expressway's existence at street level.

Oooh shiny. Clicky.

This is the second. Where the Vine Street Expressway is ideal for more fly-by-night and urbanist interventions, Society Hill is ideal for something more closely approximating garden apartments, as the image explains.
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* And usually it's not, from a technical perspective. Big Dig-type projects should usually be opposed on principle (pork-barrel automotive spending): what I am proposing here is a mitigation strategy when expressway closure has already wormed out of the picture, or for retrofitting of existing sunken expressways.
** Electricity for climate control and cooking as well as power; plumbing means fresh water and sewer hookups; fiber allows for phone, cable, and Internet.