Wouldn’t it be nice if we could create valuable new urban land by decking over freeways?

Turns out, its massively uneconomical, and doesn’t eliminate many of the most negative effects of urban freeways

Its massively uneconomical because that “land” thats created by capping freeways costs at least three times more to build than the land is worth.

While covering up a freeway made hide it from view, it does nothing to eliminate the flood of cars and their associated pollution, which simply spew out from under the covers.

Should we pay $5 to create $1 worth of urban land?

There’s a Seattle proposal to create 17 acres of land in the center of the city by building a cap over I-5.  Rough estimates are that the cap would cost up to $2.5 billion.  Long division tells us that creating an acre of land would cost $150 million (that’s without any improvements, and likely without the cost of necessary utilities or adequate substructure to support buildings).  For reference, the average value of square foot of downtown property in Seattle ranges between $500 and $1,500 per square foot.  Even if land over the freeway were worth the midpoint of that range, about $1,000 per square foot, that means an acre of land is worth about $43 million, and 17 acres, in theory, would be worth $700 million or more.  But at typically land needs to be dedicated to street rights-of-way and the net buildable land would perhaps be 80 percent of the total, worth about $500 million or so.

In Seattle, cover proponents argue that the cost of the newly created land can be offset by selling it off for development as apartments or offices.  But no one can afford to pay anything approaching the actual cost of creating such land; at best land sales might recoup a small fraction of the cost of And a $2.5 billion cost estimate for a freeway cover is highly suspect.  On its face, spending $2.5 billion to create $500 million worth of land is a value-destroying proposition.

Washington’s Legislature is likely to pull the plug on a far simpler cover proposed for State Route 520 because of a 70 percent cost overrun.  Portland’s I-5 Rose Quarter project shows how much the price tag of freeway caps can balloon:  the project, featuring a cap over I-5 near downtown Portland has quadrupled from $450 million in 2017 to $1.9 billion last year.

The Rose Quarter project also reveals some of the difficulties with creating covers that can support buildings.  Not all of the land on the covers can be built upon:  some structural elements of the cover have to be kept clear.  Even the parts that can be built on may be restricted to “lightweight” structures.

The perpetrators are asking their victims to pay for fixing the damage done to cities

And finally, there is the issue of who will pay.  Everyone agrees that caps are nice things to have, but highway departments are remarkably loathe to actually pay the cost of patching the scars they’ve inflicted on the urban landscape.

In Austin, TXDOT has flatly refused to pay the cost of “stitches” over a widened I-35 freeway, and is passing the entire cost off to the City of Austin, which will have to come up with as much as $800 million.   The stitches (small bridges with pedestrian amenities) and caps (block long or longer covers), would also have to be maintained by the city at a cost estimated at as much as $48 million a year.

In Dallas:  Cost of trenching I-345 rose from $1 billion to $1.6 billion; and of course, that price tag doesn’t include the cost of covering the freeway, which TX DOT won’t pay for, but instead will become the responsibility of the City of Dallas.

In Denver, Colorado spent roughly 10 percent of the cost of its $1.3 billion I-70 freeway widening project to build a four-acre park atop the roadway.  Neighborhood residents are still concerned about pollution levels near the freeway.

In Portland—where a mile and half long freeway widening project has exploded in cost from $450 million to $1.9 billion—the Oregon Department of Transportation claims it can’t legally pay for any supporting structures beyond those needed to hold up the roadway itself—and that someone else will have to pay the costs of beams strong enough to support buildings.

It’s nice to imagine a world where urban highways didn’t gouge massive scars on city neighborhoods.  And predictably attractive green artistic renderings of what a covered area might look like are, at least when viewed from a distance, more attractive than noisy car-choked roadways.  But as a way to create more urban land, decking over highways is one of the most expensive ways to expand our urban area.  And, in a just world, the highway agencies that carved the scars across the nation’s cities would pay to repair the damage done, in the form of replacing the homes and businesses they destroyed; but in reality, highway agencies plan to foist most of the costs of covers, caps and stitches onto their victims:  the cities eviscerated by highway construction.