Much of Philadelphia's Chinatown was demolished in the 1980s to build a sub-grade yet uncapped I-676 (the "Vine Street Expressway"). In other words, planners chose to run the highway through a...
Much of Philadelphia's Chinatown was demolished in the 1980s to build a sub-grade yet uncapped I-676 (the "Vine Street Expressway"). In other words, planners chose to run the highway through a highly dense area of the city—literally the center of the city—largely disconnecting what was a vibrant, active neighborhood in order to increase automobile throughput in an urban area.
The most offensive part is that the highway is not a tunnel: it's uncapped. It is difficult to explain how stupendously bad this decision was. If you walk to the VSE, you're greeted by multiple lanes of fast-moving at-grade traffic with an obnoxious centerpiece: faster-moving and much, much louder traffic. There is a reason many people in Center City don't cross the VSE. It fundamentally separates North Philadelphia from the rest of the city for no good reason, clearly contributing to geographic income inequality. In addition to spending billions of dollars on car-centric infrastructure that required the demolition of many historic and culturally relevant structures, noise and pollution generated by the highway is constantly felt in the neighborhood. It's almost offensive. 676 floods occasionally, costing hundreds of millions in repairs, and contributes negatively to the city's traffic problem.
This article is about the city's recent plans to construct a "cap" on a section of the highway that runs through Chinatown. The hope is that building this, probably with a park on top, will help repair the communal fabric that was ripped apart by foolish highway engineers 40 years ago. Philly hopes to fund the project with grants from Biden's 2021 Bipartisan Infrastructure Law, as well as a few assorted sources including other federal programs, local taxes, PennDOT, and some private foundations.
Construction will begin in... 2028. Who knows when it will be finished?
City officials on Tuesday unveiled three design concepts for the highly-anticipated project in Philadelphia, which would reconnect the north and south sides of Chinatown. The goal is to help right historic inequities, while making the ethnic enclave a safer and healthier place to live and work.
The concepts are fairly similar in scope. Each version of the cap, dubbed the Chinatown Stitch, would cover the expressway roughly between 10th and 13th Streets. Every design includes green space, room for public plazas, and traffic-calming measures — priorities voiced during a months-long community engagement process led by the city and the Philadelphia Chinatown Development Corporation.
The more feasible design would run 2 ½ blocks. But the other two would cap three full blocks, meeting the state’s definition of a tunnel. The designation would require more capital because crews would need to install additional infrastructure related to ventilation, fire suppression, and security.
None of the designs have public price tags yet, said Christopher Puchalsky, director of policy and strategic initiatives at the city’s Office of Transportation, Infrastructure and Sustainability. Officials have said it could cost between $25 million and $30 million per block for just the cap’s structural elements.
Philadelphia is currently in the process of capping a small portion of I-95 (another destructive urban highway) in order to reconnect Old City and Society Hill with the Delaware River, by Penn's Landing. Construction has technically begun (as of September 6), with the Walnut Street Bridge being closed before it's demolished in order to eventually build the cap. The project will create a massive 11.5 acre park between Chestnut and Walnut Streets, giving direct pedestrian and bike access to the waterfront in a way the current bridges don't truly provide. I expect that the new amenity will become a big destination for locals. The timeline has fluctuated a bit, but construction would finish not earlier than 2026 and probably more like 2028.
676 is basically a trench in the ground with bridges crossing it at each block. A highway cap is a layer of concrete that can go over the top of a trench highway like 676. From the highway's...
676 is basically a trench in the ground with bridges crossing it at each block. A highway cap is a layer of concrete that can go over the top of a trench highway like 676. From the highway's perspective, it's a ceiling. With a cap, an open-air highway effectively becomes a tunnel. From the pedestrian's perspective, it's a floor. There are other names for it, like "highway lid" or "deck." You can add layers of dirt and rocks above the structure to emulate a natural park. Highway caps have the immediate benefit of increasing available land for a city, but I personally think the greatest benefit is that they improve livability of the surrounding area. Highways are loud and unpleasant and people just don't want to be near them. Replace a highway with a park or gathering space, and suddenly a depressing neighborhood becomes a lively one.
A highway lid is a carefully engineered structure, so even if it has green space on top, it's complicated and expensive to build. It also has to be constructed without seriously affecting highway traffic. It's better thought of as a veeeery wide bridge than as a simple ceiling/floor, because it has to straddle a considerable distance and take a meaningful amount of weight above. Sometimes, if walls are required, it's more like a building. If additional structures are later going to be added on top, a cap has significantly higher engineering requirements to support the extra weight (they usually don't go for this because it's too expensive). In the case of 676 I think it will mostly be green space or plazas, but the designs aren't finalized.
While I generally approve of highway lids (because they demonstrably improve the quality of life of people who live near highways), I disapprove of large highways in general and urban highways in particular. Some activists find that city officials use highway caps as a way to appease the public while simultaneously expanding highways to appease drivers, which typically ends up worsening traffic while costing billions of dollars. That's kind of true, but also not strictly a consequence of a cap per se. It's possible to cap a highway and then... not expand it. Frankly I don't think most of the interstates are going anywhere and I would rather "stitch" together the neighborhoods that were injured by the highways back in the day. IMO you can't let "perfect" be the enemy of "better."
Sadly green space should also exclude any sizeable tree given how the root structure can and will try to burrow through said cap. A community garden kinda thing could work well though.
Sadly green space should also exclude any sizeable tree given how the root structure can and will try to burrow through said cap.
A community garden kinda thing could work well though.
I suppose it depends on the tree, as well as how much soil they put on top of the structure. Some roots tend to spread laterally while others go deeper (more taprooted). Roots are also adaptable...
I suppose it depends on the tree, as well as how much soil they put on top of the structure. Some roots tend to spread laterally while others go deeper (more taprooted). Roots are also adaptable and may prefer lateral growth in general if deeper growth is tough. Engineers can specifically design root barriers for structures like this.
I'm not an arborist, but I think you can have reasonably large trees with about 3–4 feet of soil. The highway is probably just deep enough to accommodate this if the park is slightly raised (like the park behind Independence Hall). These trees would certainly be able to offer shade, which I think is the most immediately useful benefit. Obviously, bigger trees can be better for an ecosystem, but I imagine you would need 4–6 feet of soil at least for that (again, I'm inventing these numbers). I don't think we'll be seeing any towering London planes à la Philly's Washington Square on top of a highway cap, but 20-footers are within reason.
Kansas City is looking into something similar with the portion of I-670/70 that goes right through downtown and underneath the Bartle Hall Convention Center. The plan is to put some large...
Kansas City is looking into something similar with the portion of I-670/70 that goes right through downtown and underneath the Bartle Hall Convention Center. The plan is to put some large greenspace on the cap.
I own a car. I'm a driver. But we have to start clawing back some of this space for people again.
*Note that I'm talking about two different sections of "I-70," that are confusingly named. Lived in KC for 30yrs and still don't know which segment is which.
Much of Philadelphia's Chinatown was demolished in the 1980s to build a sub-grade yet uncapped I-676 (the "Vine Street Expressway"). In other words, planners chose to run the highway through a highly dense area of the city—literally the center of the city—largely disconnecting what was a vibrant, active neighborhood in order to increase automobile throughput in an urban area.
The most offensive part is that the highway is not a tunnel: it's uncapped. It is difficult to explain how stupendously bad this decision was. If you walk to the VSE, you're greeted by multiple lanes of fast-moving at-grade traffic with an obnoxious centerpiece: faster-moving and much, much louder traffic. There is a reason many people in Center City don't cross the VSE. It fundamentally separates North Philadelphia from the rest of the city for no good reason, clearly contributing to geographic income inequality. In addition to spending billions of dollars on car-centric infrastructure that required the demolition of many historic and culturally relevant structures, noise and pollution generated by the highway is constantly felt in the neighborhood. It's almost offensive. 676 floods occasionally, costing hundreds of millions in repairs, and contributes negatively to the city's traffic problem.
This article is about the city's recent plans to construct a "cap" on a section of the highway that runs through Chinatown. The hope is that building this, probably with a park on top, will help repair the communal fabric that was ripped apart by foolish highway engineers 40 years ago. Philly hopes to fund the project with grants from Biden's 2021 Bipartisan Infrastructure Law, as well as a few assorted sources including other federal programs, local taxes, PennDOT, and some private foundations.
Construction will begin in... 2028. Who knows when it will be finished?
Philadelphia is currently in the process of capping a small portion of I-95 (another destructive urban highway) in order to reconnect Old City and Society Hill with the Delaware River, by Penn's Landing. Construction has technically begun (as of September 6), with the Walnut Street Bridge being closed before it's demolished in order to eventually build the cap. The project will create a massive 11.5 acre park between Chestnut and Walnut Streets, giving direct pedestrian and bike access to the waterfront in a way the current bridges don't truly provide. I expect that the new amenity will become a big destination for locals. The timeline has fluctuated a bit, but construction would finish not earlier than 2026 and probably more like 2028.
Can you briefly explain what a cap is in the context of highway design, please?
Oh I see. Like cut-and-cover, but all cover, no cut.
676 is basically a trench in the ground with bridges crossing it at each block. A highway cap is a layer of concrete that can go over the top of a trench highway like 676. From the highway's perspective, it's a ceiling. With a cap, an open-air highway effectively becomes a tunnel. From the pedestrian's perspective, it's a floor. There are other names for it, like "highway lid" or "deck." You can add layers of dirt and rocks above the structure to emulate a natural park. Highway caps have the immediate benefit of increasing available land for a city, but I personally think the greatest benefit is that they improve livability of the surrounding area. Highways are loud and unpleasant and people just don't want to be near them. Replace a highway with a park or gathering space, and suddenly a depressing neighborhood becomes a lively one.
A highway lid is a carefully engineered structure, so even if it has green space on top, it's complicated and expensive to build. It also has to be constructed without seriously affecting highway traffic. It's better thought of as a veeeery wide bridge than as a simple ceiling/floor, because it has to straddle a considerable distance and take a meaningful amount of weight above. Sometimes, if walls are required, it's more like a building. If additional structures are later going to be added on top, a cap has significantly higher engineering requirements to support the extra weight (they usually don't go for this because it's too expensive). In the case of 676 I think it will mostly be green space or plazas, but the designs aren't finalized.
While I generally approve of highway lids (because they demonstrably improve the quality of life of people who live near highways), I disapprove of large highways in general and urban highways in particular. Some activists find that city officials use highway caps as a way to appease the public while simultaneously expanding highways to appease drivers, which typically ends up worsening traffic while costing billions of dollars. That's kind of true, but also not strictly a consequence of a cap per se. It's possible to cap a highway and then... not expand it. Frankly I don't think most of the interstates are going anywhere and I would rather "stitch" together the neighborhoods that were injured by the highways back in the day. IMO you can't let "perfect" be the enemy of "better."
Sadly green space should also exclude any sizeable tree given how the root structure can and will try to burrow through said cap.
A community garden kinda thing could work well though.
I suppose it depends on the tree, as well as how much soil they put on top of the structure. Some roots tend to spread laterally while others go deeper (more taprooted). Roots are also adaptable and may prefer lateral growth in general if deeper growth is tough. Engineers can specifically design root barriers for structures like this.
I'm not an arborist, but I think you can have reasonably large trees with about 3–4 feet of soil. The highway is probably just deep enough to accommodate this if the park is slightly raised (like the park behind Independence Hall). These trees would certainly be able to offer shade, which I think is the most immediately useful benefit. Obviously, bigger trees can be better for an ecosystem, but I imagine you would need 4–6 feet of soil at least for that (again, I'm inventing these numbers). I don't think we'll be seeing any towering London planes à la Philly's Washington Square on top of a highway cap, but 20-footers are within reason.
Kansas City is looking into something similar with the portion of I-670/70 that goes right through downtown and underneath the Bartle Hall Convention Center. The plan is to put some large greenspace on the cap.
There's also an idea to get rid of altogether the 70/670 segment that's like 10 blocks north of I-70. This would fully reconnect Downtown to the Historic River Market District. There's a popular comparison picture that floats around reddit that shows what that segment of the interstate did to the city.
I own a car. I'm a driver. But we have to start clawing back some of this space for people again.
*Note that I'm talking about two different sections of "I-70," that are confusingly named. Lived in KC for 30yrs and still don't know which segment is which.