How costly is it to build above freeways?

[kernals12]

A growing number of cities are installing "deck parks" above their expressways. And in a few places, especially in and around Boston it seems, they're constructing entire buildings above expressways.

Now, we've all heard the criticisms of urban highways that they displace huge numbers of people and divide communities. But it's clearly possible to build over these roads. Since they don't do this everywhere even though it's pretty obviously positive and satisfies everyone, am I right in assuming that it's catastrophically expensive?

[Dirt Roads]

Costly, but not astronomical.  The airport industry constructs the guideways for roads, rail transit and automated people movers every which way (on top of buildings, beneath buildings and through buildings), as well as constructing buildings and parking decks over these transportation facilities.  I'm not a structural engineer, but the concept is basically to bridge over the void and construct the building onto the bridge (or straddling the bridge).  A big piece of the puzzle is how long can you live with the highway being closed to traffic while the cranes are operating.  Some urban highways cannot be closed for 6 to 8 hours, even in the dead of night. 

There are many other factors that constrain this type of development.  The possibility of failure during construction probably being most important.

[Dirt Roads]

I'm not a structural engineer, but the concept is basically to bridge over the void and construct the building onto the bridge (or straddling the bridge).  A big piece of the puzzle is how long can you live with the highway being closed to traffic while the cranes are operating.  Some urban highways cannot be closed for 6 to 8 hours, even in the dead of night. 

By the way, the design loads and stiffening for resonance frequencies for construction of these types of structures are way different than for highway bridges.

[ilpt4u]

A growing number of cities are installing "deck parks" above their expressways. And in a few places, they're constructing entire buildings above expressways.

I feel like this isn't exactly a "new"  phenomenon. Hubbard's Cave in Chicago along the Kennedy Expressway has been developed land above the Expressway for a long while

I guess the Park/Plaza above Old I-70/Now I-44 in Downtown St Louis, reconnecting the Courthouse to the Arch and the Riverfront is much more recent

[kernals12]

Costly, but not astronomical.  The airport industry constructs the guideways for roads, rail transit and automated people movers every which way (on top of buildings, beneath buildings and through buildings), as well as constructing buildings and parking decks over these transportation facilities.  I'm not a structural engineer, but the concept is basically to bridge over the void and construct the building onto the bridge (or straddling the bridge).  A big piece of the puzzle is how long can you live with the highway being closed to traffic while the cranes are operating.  Some urban highways cannot be closed for 6 to 8 hours, even in the dead of night. 

There are many other factors that constrain this type of development.  The possibility of failure during construction probably being most important.

If it was this simple, you'd think they'd have done it when they were building the highways in the first place. And in fact, in the late 60s, highway engineers tried proposing air rights developments to revive their unpopular highway proposals, most famous was Paul Rudolf's brutalist ambitions for the Lower Manhattan Expressway.

Caltrans jumped through a lot of hoops to get the Century Freeway built. They installed sound barriers and built 4000 units of replacement housing as part of the 1981 Plea Agreement. The result was the 105 being the most expensive interstate highway in US history per mile. If it was simple to just build new housing on top of the freeway, which would also eliminate the noise problems, I'm pretty sure they would've done it.

[kernals12]

The high cost of building elevated structures is pretty evident everywhere. If it was cheap, then lots of things would be different:

All cloverleaf interchanges would be replaced by 4 level stacks
Almost every arterial street would have grade separated intersections
Sidewalks and crosswalks would be replaced by elevated walkways
Parking lots would be located underneath buildings to save space
Sports stadiums would all be domed over
There'd be a lot more indoor shopping malls
Monorails and Personal Rapid Transit Systems would be ubiquitous

But none of that is true, for good reason

[Ned Weasel]

There'd be a lot more indoor shopping malls

Once upon a time, there were.

[Dirt Roads]

Costly, but not astronomical.  The airport industry constructs the guideways for roads, rail transit and automated people movers every which way (on top of buildings, beneath buildings and through buildings), as well as constructing buildings and parking decks over these transportation facilities.  I'm not a structural engineer, but the concept is basically to bridge over the void and construct the building onto the bridge (or straddling the bridge).  A big piece of the puzzle is how long can you live with the highway being closed to traffic while the cranes are operating.  Some urban highways cannot be closed for 6 to 8 hours, even in the dead of night. 

There are many other factors that constrain this type of development.  The possibility of failure during construction probably being most important.

If it was this simple, you'd think they'd have done it when they were building the highways in the first place.

Not sure how any of this looks simple.  From working on many projects limited to late night staging, it is very expensive and much slower than brownfield work in the daylight.  Anyhow, economics will cause developers to gravitate to the most profitable alternatives. 

Before COVID, some cities were experiencing very high occupancy rates and limited options for development.  Development over highways (particularly subgrade highways) appeared to be less expensive (and certainly faster) than the turnaround for acquisition of an old high-rise, demolition and construction.  But it is a tough sell with a lot of risks (many that are safety- and security-related).  Given that the current economics for urban development are bleak, I think this is a mind exercise for now.

And in fact, in the late 60s, highway engineers tried proposing air rights developments to revive their unpopular highway proposals, most famous was Paul Rudolf's brutalist ambitions for the Lower Manhattan Expressway.

It is sad that certain highways (and transit systems) became unpopular.  Fortunately, Manhattan sprang back to life when I was working there throughout the 1990s. 

[kernals12]

Costly, but not astronomical.  The airport industry constructs the guideways for roads, rail transit and automated people movers every which way (on top of buildings, beneath buildings and through buildings), as well as constructing buildings and parking decks over these transportation facilities.  I'm not a structural engineer, but the concept is basically to bridge over the void and construct the building onto the bridge (or straddling the bridge).  A big piece of the puzzle is how long can you live with the highway being closed to traffic while the cranes are operating.  Some urban highways cannot be closed for 6 to 8 hours, even in the dead of night. 

There are many other factors that constrain this type of development.  The possibility of failure during construction probably being most important.

If it was this simple, you'd think they'd have done it when they were building the highways in the first place.

Not sure how any of this looks simple.  From working on many projects limited to late night staging, it is very expensive and much slower than brownfield work in the daylight.  Anyhow, economics will cause developers to gravitate to the most profitable alternatives. 

Before COVID, some cities were experiencing very high occupancy rates and limited options for development.  Development over highways (particularly subgrade highways) appeared to be less expensive (and certainly faster) than the turnaround for acquisition of an old high-rise, demolition and construction.  But it is a tough sell with a lot of risks (many that are safety- and security-related).  Given that the current economics for urban development are bleak, I think this is a mind exercise for now.

And in fact, in the late 60s, highway engineers tried proposing air rights developments to revive their unpopular highway proposals, most famous was Paul Rudolf's brutalist ambitions for the Lower Manhattan Expressway.

It is sad that certain highways (and transit systems) became unpopular.  Fortunately, Manhattan sprang back to life when I was working there throughout the 1990s.

And as I suspected, it is horrendously expensive. The Klyde Warren Park over the Woodall Rogers Freeway in Dallas cost $110 million for 5.2 acres. That's $20 million per acre!

[CtrlAltDel]

And as I suspected, it is horrendously expensive. The Klyde Warren Park over the Woodall Rogers Freeway in Dallas cost $110 million for 5.2 acres. That's $20 million per acre!

On a completely irrelevant side note, what do you think this is:

[US 89]

And as I suspected, it is horrendously expensive. The Klyde Warren Park over the Woodall Rogers Freeway in Dallas cost $110 million for 5.2 acres. That's $20 million per acre!

On a completely irrelevant side note, what do you think this is:

Looks like it carries a pipe of some sort over the highway.

[kphoger]

It appears to be electrical.

There is conduit on top of the beam and utility access adjacent.  In the second GSV shot (and in the first one if you pan around a little), you can see red paint and flags, which are indicative of electrical lines.

[kernals12]

There'd be a lot more indoor shopping malls

Once upon a time, there were.

Most of the malls ever built are still open. And they charge rent that is twice as high per square foot as a regular strip mall due to the cost of the roof.

[STLmapboy]

I guess the Park/Plaza above Old I-70/Now I-44 in Downtown St Louis, reconnecting the Courthouse to the Arch and the Riverfront is much more recent

That one doesn't even feel like a tunnel, just a bit more bridge over the highway.

[CtrlAltDel]

It appears to be electrical.

There is conduit on top of the beam and utility access adjacent.  In the second GSV shot (and in the first one if you pan around a little), you can see red paint and flags, which are indicative of electrical lines.

Interesting. Thanks for the detective work. My best guess was that it was a "If you hit this sign, you will hit that bridge," sort of thing, but that made wonder why there wasn't one on the other side.

[Ned Weasel]

Most of the malls ever built are still open.

Citation?  The only areas I've been to where lots of malls were still open were the Greater New York, Greater Chicago, and Greater Los Angeles areas.  If you go just about anywhere else in the country, most metropolitan areas that aren't huge used to have maybe a dozen or so malls but are now down to just one or two.

And they charge rent that is twice as high per square foot as a regular strip mall due to the cost of the roof.

I don't doubt that part.

[hotdogPi]

Most of the malls ever built are still open.

Citation?  The only areas I've been to where lots of malls were still open were the Greater New York, Greater Chicago, and Greater Los Angeles areas.  If you go just about anywhere else in the country, most metropolitan areas that aren't huge used to have maybe a dozen or so malls but are now down to just one or two.

Quite a lot in this area.

[kernals12]

Most of the malls ever built are still open.

Citation?  The only areas I've been to where lots of malls were still open were the Greater New York, Greater Chicago, and Greater Los Angeles areas.  If you go just about anywhere else in the country, most metropolitan areas that aren't huge used to have maybe a dozen or so malls but are now down to just one or two.

And they charge rent that is twice as high per square foot as a regular strip mall due to the cost of the roof.

I don't doubt that part.

Most of the malls ever built in the US are still open.
https://en.wikipedia.org/wiki/List_of_shopping_malls_in_the_United_States

[kernals12]

Most of the malls ever built are still open.

Citation?  The only areas I've been to where lots of malls were still open were the Greater New York, Greater Chicago, and Greater Los Angeles areas.  If you go just about anywhere else in the country, most metropolitan areas that aren't huge used to have maybe a dozen or so malls but are now down to just one or two.

Quite a lot in this area.

For the purpose of luring Bay Staters to shop sales tax free in New Hampshire.

[Ned Weasel]

Most of the malls ever built in the US are still open.
https://en.wikipedia.org/wiki/List_of_shopping_malls_in_the_United_States

That list includes many open-air shopping centers, a mall that was demolished and redeveloped without being noted in the list ( https://en.wikipedia.org/wiki/Winrock_Town_Center ), and a mall that closed almost three years ago without being noted in the list ( https://en.wikipedia.org/wiki/Crossroads_Mall_(Oklahoma) ).

And for the truly enclosed malls that do still be happen to be open, I have to wonder how many of them are on their deathbeds, with a majority of retail spaces either vacated or converted to other uses.

[Bruce]

Seattle has quite a few park lids, the oldest being Freeway Park over I-5, opened in 1976. The original idea was to build a larger version on top of the freeway as it was constructed, but it was shot down for being too costly. The eventual version is only two blocks long and is a Brutalist relic that hasn't aged all that well despite being carefully designed.



A decade later, we built a convention center over an adjacent block and it turned out to be a great use of the space.



Of course there are also the I-90 lids on Mercer Island and the newer series of lids on SR 520 (including two that have yet to be built).

[michravera]

A growing number of cities are installing "deck parks" above their expressways. And in a few places, especially in and around Boston it seems, they're constructing entire buildings above expressways.

Now, we've all heard the criticisms of urban highways that they displace huge numbers of people and divide communities. But it's clearly possible to build over these roads. Since they don't do this everywhere even though it's pretty obviously positive and satisfies everyone, am I right in assuming that it's catastrophically expensive?

It's one thing (fairly simple) to build a park or even a few odd structures (even fairly tall ones) over a small portion of an existing roadway. It's something else again to build a entire  neighborhood along and atop the entire roadway.
If you have a 100 m right of way, you can build a fair sized park by covering over a couple hundred meters of it. The loads for a park aren't terribly large (People even standing hip-to-hip don't impose anywhere near the load of trucks rolling along), and you could, with good planning, keep people and vehicles to the places where the load bearing capability is sufficient.
Likewise, you could, fairly easily, build a tall structure that distributes its loads at a level a few meters above the roadway and have two carriageways each 20 or 30 m basically go under the structure (with a 30 m load bearing section in the middle and plenty of room on each side).

What gets monstrously expensive is to subduct a entire 100 m right of way for tens of kilometers.

[kernals12]

A growing number of cities are installing "deck parks" above their expressways. And in a few places, especially in and around Boston it seems, they're constructing entire buildings above expressways.

Now, we've all heard the criticisms of urban highways that they displace huge numbers of people and divide communities. But it's clearly possible to build over these roads. Since they don't do this everywhere even though it's pretty obviously positive and satisfies everyone, am I right in assuming that it's catastrophically expensive?

It's one thing (fairly simple) to build a park or even a few odd structures (even fairly tall ones) over a small portion of an existing roadway. It's something else again to build a entire  neighborhood along and atop the entire roadway.
If you have a 100 m right of way, you can build a fair sized park by covering over a couple hundred meters of it. The loads for a park aren't terribly large (People even standing hip-to-hip don't impose anywhere near the load of trucks rolling along), and you could, with good planning, keep people and vehicles to the places where the load bearing capability is sufficient.
Likewise, you could, fairly easily, build a tall structure that distributes its loads at a level a few meters above the roadway and have two carriageways each 20 or 30 m basically go under the structure (with a 30 m load bearing section in the middle and plenty of room on each side).

What gets monstrously expensive is to subduct a entire 100 m right of way for tens of kilometers.

No it's not. These caps go for tens of millions of dollars per acre. That's a lot of money. It takes a lot of steel and concrete to keep these lids from falling.

[BridgesToIdealism]

I'll note for the record that Boston has done this with the Western Expressway (the section of the Mass Pike inside Route 128)... in fact, they've done it multiple times within a short stretch of highway (Star Market, Prudential, etc.)

[6a]

Here is info about the I-670 cap in Columbus, Ohio. While not a park, it's actually three separate bridges. One for the street and one each for the buildings on either side.

Sorry for the PDF

https://casestudies.uli.org/wp-content/uploads/2015/12/C035010.pdf