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The Diverging Diamond

A couple of weeks ago, I ran a short blurb in a Friday News Digest about the idea of a diverging diamond interchange. Here's what I said:

Speaking of videos and engineers, did we need more proof that the engineering profession is insane than this video of the "diverging diamond". If we had infinite resources (we don't), this would still be crazy, but the fact that we're broke just shows you how insulated from reality so many of them are. Hey, engineers -- watch my TED talk on the difference between a ROAD and a STREET. You're trying to rid yourself of accident-prone left turns? Well, how about just build ROADS where there is no need for left turns and STREETS where they are no problem, instead of the STROADS you build today. I'm not joking.

There were some hard feelings in the comments section about my categorization of the diverging diamond -- and the egineering profession that developed it -- as insane. In a spirited discussion, one of our readers posted a video of an engineer giving an enthusiastic tour of the pedestrian features of one diverging diamond. For me, it was irresistible.

The following video is my "response". Sometimes I feel as if I'm shouting into the wind with the engineering profession. This may just be more of that. If nothing else it was theraputic to me. Hopefully it provides some value and insight for our readers.

As a final note; while I acknowledge that I did pick and choose the comments of the enthusiastic engineer that I wished to highlight, I did not edit the video or his comments. I don't think I took any out of context either. Please listen for yourself and see if you agree with my "insanity" assessment.

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Reader Comments (21)

Chuck -

I think you would be hard pressed to find any cycling advocate who thinks this is positive. But it makes clear that "complete streets" can be used to describe environments that are designed to be hostile to both pedestrians and cyclists. The goal of this intersection is to channel pedestrians and cyclists so that they don't interfere with the movement of motor vehicles.

When I asked a MnDOT engineer how I was supposed to get across the street on my bike if the new traffic lights didn't change at night except for motor vehicles, he responded "what are you doing out riding your bike at night?" The Grand Rapids traffic engineer said - just run the red light. As it turned out the lights don't ever change, day or night, unless you are driving a vehicle large enough to activate the light. But whether the light changes or not, they still stop pedestrians from crossing just in case. Those are the folks who are going to implement "complete streets".

The answer to the question of whether a blind person would use the facilities provided may surprise you. They will if they have to. But that would be the same answer for any pedestrian or cyclist. These are "welfare" facilities, designed to provide minimal service to those who are disadvantaged by their lack of a motor vehicle.

Part of the problem here is that we are letting our public spaces be "designed" by engineers. Think about what our homes would be like if they were designed by engineers. Cinder block walls, its fire proof! No windows, more energy efficient. Concrete floors, durable and easy to maintain. The Soviet Union let engineers build housing and, while it wasn't quite that bad, pretty much any aesthetic considerations that added costs were considered counter-revolutionary. I think we have engineers designing Soviet style roads. And the example of the red brick in the video just one example of how that plays out.

Part of the difficulty with transforming places like the one you see, is that the question of where do you start? Looking short term, putting in facilities for pedestrians and cyclists often looks like a waste of money. As you point out, who is going to be out walking in a place like this. But you can't just wave a magic wand and transform it. It is going to take a long time and require investments that will only be returned years later.

About ten years ago, I spoke to a community group in North Plains Oregon where they had a new development being planned on half of what was an RV sales lot. The community folks wanted the design changed to move the building up to the street so that they would be accessible to pedestrians. The developer wanted to know why he was being required to put in sidewalks when there were no sidewalks around the property and no pedestrians to use them. The answer, from the community group, was that if he didn't put in sidewalks, then why would the next development? If he stuck his building behind a large parking lot, then why wouldn't the next development? This developer was actually pretty reasonable. Those answers made sense to him (not that he wanted to spend money on sidewalks) and he didn't really care where the office building was located on the lot. If it would make the neighbors happier and get his project approved, he was perfectly amenable to it. When I left, he had his site plan out and was asking for feedback from the people there. But the key to that happening was a group of people with a long range vision for their auto-dependent community restoring its small town environment. Here is a link to the Google street view of the result: http://g.co/maps/vbgc3 Its going to be a long time before those investments pay for themselves.

November 7, 2011 | Unregistered CommenterRoss Williams

Nicely done Chuck... and the absurdities of this being pedestrian friendly have been exposed.

But isn't the point of the bridge and this interchange to move traffic? I realize we want ped and bike friendly crossings and intersections, but this isn't mainstreet... why the heck would anyone be walking across this bridge anyway?

I imagine the whole ped/bike trench was, as you said, the solution after the issue of moving traffic was solved. Just imagine how much money they saved with installing that pretty decorative red rock instead of building a separate bike/ped bridge!

November 7, 2011 | Unregistered Commentergml4

George - Absolutely, the point of the bridge and interchange is to move traffic. Period. There is no other design consideration that is taken seriously.....not pedestrian movement, not cycling and certainly not building something that will create any capturable value. The claims by the engineer giving the tour that this interchange is "pedestrian friendly" demonstrates what engineers view as "pedestrian friendly" -- a despotic trench, some red bricks and a few raised markings.

We need to build environments that provide more value -- real financial value that can be captured by people, businesses and governments. These despotic places meet all of the engineering checklists, but provide no real value. We need to stop kidding ourselves that, just because we meet a "Complete Streets" punchlist, we've designed a place worth building.

If engineers want to suggest this is a brilliant way to move cars, so be it. We can then debate whether or not moving cars is something worth this level of investment. But when they suggest that a design like this is somehow multi-modal -- that it is actually "friendly" for pedestrians and cyclists -- it should make it clear that we need to reduce the engineering profession's role in designing public spaces.


November 7, 2011 | Unregistered CommenterCharles Marohn

Enjoyed the video and points greatly. The 'checking a box' criteria is indicative of this quote by Aldo Rossi, "In America, Quantity is Quality." Those boxes had metrics responding to quantities, leaving the quality of a place left to chance, at best. Engineering builds for quantities (ADTs, EDUs, VMTs, LOS), General Services builds public buildings (value engineering out civic beauty), Parks and Recreation builds public spaces (1 ac per 1,000 people), and planning is about regulating private land (14 du/ac). All being equal as silo departments, and none are able to control quality except when it goes up to the mayor and city council, who should not be making intersection design decisions. And neither should our planning groups and design review boards be making those decisions too. We need an overhaul of our planning and development department organizations to step forward and realize the economic potential of building towards quality places. Your intersection could have been anywhere, thus it was nowhere, and with nobody to concern themselves with the economic potential of that placeless area. In the end, the video is of money wasted.

November 7, 2011 | Unregistered CommenterHoward Blackson

Bravo. Video is a great way to not only explain the Strong Towns philosophy, but to show it as well. Definitely adds to the conversation, thank you.

November 7, 2011 | Unregistered CommenterForaker

You make some great points in this video, but I have to add that they've really gone out of their way to make diverging diamonds unfriendly to pedestrians. For one thing, there's really no need to force pedestrians into the death star trench. This is actually the most damning thing about the design, because it is just as safe to allow pedestrians to continue along the outside of the intersection, but of course it is less convenient for drivers to have to yield at the crossings.

It is true, though, that as designed, these pedestrian crossings are dangerous. That's because they design the crossing for the driver's convenience, and not the pedestrian's. By creating an extremely shallow turning radius they allow the driver to turn without hardly slowing down, but they force the pedestrian to look over their shoulder to cross, which of course is dangerous and uncomfortable. If they had made a sharper angle to the turns, they could have improved pedestrian safety.

But as you point out, they are not interested in pedestrian safety or convenience. I'd be curious to see if such a diverging diamond could be designed.

November 7, 2011 | Unregistered CommenterAlex

Sorry to state the obvious, but this is a freeway interchange. Designing it to be a pleasant beautiful place to be is about as absurd as expecting a lakefront promenade to move cars at 60 mph. Expecting some basic level of safety is about what is realistic. If we are going to make communities safe, quality places. It is best to focus our limited (very limited) resources on places where pedestrians are now and work out from there. The engineer was proud of the design, which shows just how far we have to go. A more honest assessement is that this is the best we can do here. We won't kill anybody today. Efforts to make a place a great place for people will need to start somehwere else.

November 8, 2011 | Unregistered CommenterDave Andersen

Dave -

It may not be so obvious as you think. It appears that the local high school, another school, a Bible College and a park and zoo are all slightly north of this intersection - the direction in which you are initially walking. Behind you on the south side of the freeway is a shopping district including a Walmart and a variety of restaurants like IHop and the Waffle House that you walk by. There is also a library.

So there may well be a fair amount of demand for pedestrians/cyclists to cross the freeway at that location assuming it had quality facilities. There is an alternative crossing to the east but what kind of pedestrian/cyclist facilities exist to get you from there to the shopping district is anyone's guess.

As for where to start, I think that "where" may be the wrong question. The question is WHEN and the answer is NOW. If you are doing a project and get it wrong now, chances are you are not going to come back and fix it for a very long time. Even once everyone agrees that five continuous lane highways through the middle of town are a bad idea, it will be years before MnDOT can undo the damage.

November 8, 2011 | Unregistered CommenterRoss Williams

This comment from @Ross sums it up completely. "These are "welfare" facilities, designed to provide minimal service to those who are disadvantaged by their lack of a motor vehicle."

The fact that this is a freeway interchange is indicative of the larger problem. The freeway, instead of being designed primarily to move long-distance traffic, is being asked to serve a Main Street, connecting homes to the Lowes and the school and everything else right nearby here. If the freeway was used for their intended use, and not as the main provider of local traffic, then the suggestion from some folks on here might be right that cars should be expected to be primary and pedestrians an afterthought.

But this is essentially a local street intersection, no matter what purpose the roads were originally intended to be in some planner or engineer's mind.

This is 90% of the problem with the interstate system and its current condition as it relates to congestion: we've taken something for interstate travel and expected it to become the primary facility for local travel. The logic that says, "it's a freeway intersection, it's supposed to be an auto sewer!" sums up all that's wrong with street and road design.

November 8, 2011 | Unregistered CommenterSteve

You're an idiot. You base your comments on through someone else's video. Why don't you do this interchange justice and visit the site and talk with the people from Missouri who use the intersection by car and walking.

November 8, 2011 | Unregistered CommenterPissed off

I think it's too early to blast or champion this sort of interchange design yet....better to wait until we have some operating experience with them.

Regarding traffic lights not changing for bikes, I'm not sure what sort of vehicle detectors MnDOT's using up north, but I know from personal experience that the detectors Hennepin County uses can pick up bikes...even 20 years ago.

November 9, 2011 | Unregistered CommenterFroggie

Hi there. I am the traffic engineer for the City of Austin, Texas, and I embrace a people-centric, context-sensitive approach to our roadways. My career began with a state DOT; the challenge is their business model is auto-centric because most of their facilities are rural and high-speed, yet that model begins facing significant challenges when the roadway crosses the city limits, the speed limit drops below 45 MPH, and the context changes to people-centric. Fortunately I and other colleagues who are people-centric in our approach are working with our DOT counterparts to help them develop context-sensitive designs which do better serve all roadway users - pedestrian, bicyclists, transit riders, and motorists. From MoDOT's perspective they have developed a truly innovative intersection design and indeed they should be proud. Yes, the design is auto-centric. Yes it is challenging to bicyclists and pedestrians whose needs need to be met also. Those who do understand quality of life and creation of place along with level of service should seek opportunities to help educate and guide those who may not yet have those perspectives.

November 9, 2011 | Unregistered CommenterGary Schatz

"I know from personal experience that the detectors Hennepin County uses can pick up bikes...even 20 years ago."

I know from personal experience that they can be designed that way as well. In this case they weren't and that WAS by design. The issue was raised with MnDOT prior to construction and that is when I got told to just run the red. MnDOT is paying lip service to "complete streets" for political and funding purposes, but they have no real organizational commitment to non-motorized users.

The video gives a pretty good picture of how complete streets roll out under that kind of leadership. We have plenty of operating experience with these design elements. Just try getting around on a bike or by foot on any facility built by MnDOT.

November 9, 2011 | Unregistered CommenterRoss Williams

@Ross: perhaps that's the way the outstate districts are operating, but my experience in the Metro isn't quite as bad. For example, without MnDOT, we wouldn't nearly have as many bike/ped river crossings as we do now. Nearly all the major river crossings in the Metro have a bike/ped path across them, and recent bridge replacements (I-494 Wakota, I-35E Lexington, 610, etc) have further reinforced that. With one exception, the few bridges that don't have crossings all have nearby (within 1/2mi) crossings...in the case of the Bloomington Ferry Bridge on 169, MnDOT and the county specifically replaced the old ferry bridge with a brand new bike/ped-only bridge on the same site.

November 9, 2011 | Unregistered CommenterFroggie

@Froggie -

I am sure the politics is different around the state and advocacy groups in the Twin Cities have a lot more ability to influence decisions. That said, I had the impression the Bloomington Ferry Bridge was part of a highway project that allowed MnDOT to avoid consideration of pedestrian and bike interests in the construction of their 169 highway bridge for motor vehicles. That isn't necessarily a bad thing since the most likely alternative would have been a Missouri-like accommodation for pedestrians bikes and pedestrians.

November 9, 2011 | Unregistered CommenterRoss Williams

Er...you do know this was the best the could retrofit onto the existing bridge, right? It's not a "complete streets" solution by any stretch of the imagination and it shouldn't be viewed that way. On the ones I've worked on, the center channel (and that is the best place to put it) is at least 14' wide. The right shoulder in both directions should be between 8-10' wide and striped as a bike lane. The cross section on this project reflects only what they could fit on the existing bridge. When you account for the fact that they added about 35% more capacity at a low cost and little in the way of new pavement and no work on the bridge, it's pretty remarkable. It was a functional decision. And it's leaps and bounds better for bikes and peds than it was before.

November 9, 2011 | Unregistered CommenterSmith S.

@Ross: said advocacy groups didn't quite exist 20-30 years ago, not even close to the extent they do now. At least within the Metro, MnDOT made a conscious decision to add bike/pedestrian facilities to the major river crossings where possible, and the bulk of these facilities were built in the '80s and '90s.

BTW, the Bloomington Ferry Bridge was a Hennepin County project. MnDOT eventually took it over for Hwy 169 after completion, but the only direct involvement they had was through their State Aid Division.

November 9, 2011 | Unregistered CommenterFroggie

@Froggie -

Here is what you said to begin with:

" With one exception, the few bridges that don't have crossings all have nearby (within 1/2mi) crossings...in the case of the Bloomington Ferry Bridge on 169, MnDOT and the county specifically replaced the old ferry bridge with a brand new bike/ped-only bridge on the same site."

As I understand it, the bridge replacement was identified as a bike/ped alternative in the EIS for the new Highway 169 bridge.

I think we are talking about different things. Including minimal pedestrian and bike facilities on bridges is not a sign of a commitment to serving those users. Its certainly better than nothing, but the alternative was to have cyclists and pedestrians on the roadway with motor vehicles. That would "interfere" with traffic flows.

November 9, 2011 | Unregistered CommenterRoss Williams

Great discussion, everyone. I've tried to provide a few clarifying thoughts in a new post today.


November 10, 2011 | Unregistered CommenterCharles Marohn

I found the video comments about cyclists to be ignorant and offensive. It is hardly news that it is dangerous for cyclists to ride on sidewalks, even without Death Star lasers. I saw nothing on the roadway that would endanger even a slow cyclist who was operating accordance with principles taught in almost any beginning cycling class. Hardcore? Its doubly sad because most of the pedestrian observations were on the mark.

November 12, 2011 | Unregistered CommenterSteve A
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