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Kaid Benfield’s Blog

Diamond in the rough, or a futile attempt to engineer walkability

Kaid Benfield

Posted November 14, 2011

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  a 'diverging diamond' interchange near Springfield, MO (via Google Earth)

You are looking at something called a “diverging diamond” interchange.  Don’t ask me to explain how it works or why it’s called that by civil engineers.  This particular one, west of Springfield, Missouri, marks the intersection of two major freeways.  And it’s gaining some internet notoriety for its design, which includes either an earnest attempt to create some walkability in a place that is ridiculously unwalkable no matter what you do to it, or a pro forma attempt to comply with new engineering standards regardless of context, depending on how you look at it.

The location is a place as American as apple pie with, starting in the southeast quadrant and going clockwise, a Waffle House and Econo-Lodge; a Walmart Supercenter; and a Lowe’s.  (There’s not much going on in the northeast quadrant.)

My pal Chuck Marohn of Strong Towns has started a bit of firestorm by going after the diverging diamond both in concept and in this particular instance.  Chuck believes that we need more attention to walkable streets and fewer dollars going into insanely expensive, over-engineered highways.  He has some fun with this one, doing an entertaining edit of an video someone sent him to illustrate (with approval) the state’s attempt to engineer the intersection to accommodate pedestrians and cyclists. There is little that Chuck enjoys more than going after his fellow engineers, and he contrasts the unwalkability of the diverging diamond with the true walkability of places like Amsterdam that really do put pedestrians and cyclists first.

The empire struck back, and Chuck apparently got hammered by commenters for going over the top in his comparisons.  Did he?  Maybe, given that positing a mid-America freeway interchange against central Amsterdam isn’t exactly an apples-to-apples comparison.  But Chuck’s response is abundantly fair and (literally) on the money:

“If you watch the original video that my comments were based off of, the gentlemen giving the tour was touting how pedestrian- and cycling- friendly this interchange was. That is absurd. This interchange is not "friendly" to pedestrians or cyclists. Suggestions that red decorative brick or yellow markings on the sidewalks would make it so are absurd.

“If we in the engineering profession can't step back and acknowledge the absurdity of this situation -- the absurdity that mindless adherence to standards has created -- how can we expect to be taken seriously as leaders by a country going through a difficult and painful economic transition?

“It is not good enough to simply follow the ASCE and demand ever more money for our profession when we turn around and waste it in spectacular amounts on things that provide no return (in this instance, moving cars a little faster and building expensive pedestrian/bike facilities that will never be widely used because they are despotic and demeaning). If we want to be part of the solution, we need to reorient ourselves away from our obsession with moving cars more efficiently and towards building places of value.”

Enjoy the video:


Move your cursor over the images for credit information.

Kaid Benfield writes (almost) daily about community, development, and the environment.  For more posts, see his blog's home page

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Rob P.Nov 14 2011 02:30 PM

Minor quip. This is the intersection of a limited-access road (expressway) and a surface road, not two freeways (expressways). If it were the intersection of two freeways, it would be an interchange and there wouldn't be any pedestrian access.

Karl FundenbergerNov 14 2011 02:36 PM

Wow, thanks for sharing! Great take on Chuck Marohn's thoughts.

Kaid @ NRDCNov 14 2011 02:38 PM

Thanks for that clarification, Rob.

Steve S.Nov 14 2011 05:55 PM

In Europe such an interchange would more likely be in the form of a giant roundabout. Diverging diamonds are supposed to eliminate dangerous left turns at highway interchanges, but they do so by having the interchanging (general access or secondary) road grade-cross itself at either end of the complex. These crossings, of course, need to be maintained by traffic lights. The roundabout method would execute the same maneuver without traffic lights, and permit at-interchange U-turns for all (automotive) parties to boot; however, it would need to be built with two smaller bridges rather than a single behemothic quasi-tunnel span.

It is also important to note that quasi-freeway highways, such as what interchanges with I-44 here, is far and away the least safe kind of road that exists, due to turning and mode conflicts existing at rather high speed. (True freeways eliminate turning and non-auto modes, thereby eliminating conflicts, which make them very safe at speed.)

ScottNov 14 2011 10:26 PM

Forgive me, but I am going to speak for someone I don't know. I don't believe Chuck isn't talking about engineering when he knocks the diverging diamond. From the standpoint of moving massive amounts of cars as quickly as possible and incorporating some bike and ped (however absurd), the diverging diamond probably works fine. What is being discussed is a complete cognitive dissonance between what we need and what is being built. We have constructed an environment that is not made for people. Our muni budgets are getting tighter every year, school district consolidation, slowing of intergovernmental transfers (fed>state>local>people - repeat) yet we invest our money in things that will add very little value to our lives. Often we are merely creating long term liabilities for our children.

CindyNov 15 2011 12:22 AM

Please don't show this to our traffic engineer, we're trying to get AWAY from ridiculous urban interchange baloney.

These "designs" don't support human life, never mind supporting pedestrians and bicyclists. The vistas will probably inspire a slow-moving person want to jump.

CharlesNov 15 2011 11:08 AM

Thanks Kaid. Your audience here is much kinder than the group that has flocked to the YouTube site or the piece on this in the Atlantic Cities. Rough crowds there.

I think even most traffic-obsessed engineers can acknowledge that the environment presented in the original video was despotic for pedestrians and cyclists, the "beautiful view of Highway 44" notwithstanding. That was my main point.

The reactions in defense of the Diverging Diamond have been fascinating to me, however. Especially those that have argued that it is a great way to move traffic, something I have never argued with. I think it has identified a gap in the narrative here that we need to pursue further.

Specifically, there is this ingrained thinking that our investments in surface transportation (like this interchange) should be looked at as part of a system. The professionals and their advocates seem to be arguing that we can't evaluate micro components of a system for their productivity but instead need to consider the system as a whole. They are suggesting a kind of quantum theory of surface transportation -- one that exists but eludes our ability to actually measure in its totality. We're told to just trust the engineers that have an intuitive knowledge of how this system works.

That is rubbish. Lazy thinking. We're working on a new report (tentatively titled "Misunderstanding Mobility") that is now going to also focus on this issue.

Thanks again, Kaid, for all that you do.

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