When Traffic Engineers Can’t Hear You


My wife just finished the book Left Neglected and thought the premise was unique enough to tell me about it twice. The main character suffers from a condition called “left neglect” where, because of a neurological injury, they are unable to perceive that there is a left. It’s not that they can’t hear or feel things from the left, but that they do not involuntarily recognize that there is even such a thing as left.

She gave me some examples from the book—people would be speaking and the person with left neglect couldn’t figure out where they were, even though they were standing right there on their left. And as she told me this, it was hard for me not to, metaphorically speaking, draw some parallels to some of my colleagues in the engineering profession. Except instead of left neglect, I’d call it human neglect.

You can tell an engineer that people are there. They can even take steps to acknowledge the presence of humans when prompted. But none of it is intuitive. And the results show it.

I’m going to focus on one today because I keep getting routine updates from a video I posted years ago on the Diverging Diamond Interchange (DDI). The video keeps getting passed around engineering circles as a joke, as a way to laugh at Strong Towns and discredit me. These are nearly always behind a paywall (although the sympathetic sometimes send me excerpts), but these conversations often lead to an increase in comments on the YouTube page.

For example, this was posted last week by someone identifying themselves as Luke Popez:

Seven years later....YOU WERE WRONG. About all of it. Diverging diamond has reduced fatalities by 60%.

Here’s a another in that same period from someone identified as Callie Masters:

This guy wants a highway intersection to be as friendly as a teddy bear's picnic spot. Keep your nervous kids at home! We're trying to drive fast here!!

And from James Lemay:

Turns out you were totally wrong about everything.

I was wrong about everything, the diverging diamond is safer than what it replaced, people want to drive fast so stop being such a ninny. These are very interesting assertions, especially since they respond to a contention that I never made. And THAT is the problem.

So many traffic engineers suffer from human-neglect, an inability to perceive humans in their designs. Even when forced to accommodate pedestrians— their pet term for humans—they still don’t intuitively perceive them.

My diverging diamond video was responding to an engineer who had recorded a video to show off the pedestrian-friendly design of the diverging diamond. That engineer asserted throughout the video that the DDI was pedestrian-friendly. To make his case, he noted the Jersey barrier, raised domes for the vision-impaired, decorative brick, push button crossings, and the beautiful view of the interstate, among other features.

This was then, and remains today, totally ludicrous. My video points this out. The DDI design is quintessential checklist engineering: an approach that goes through the motions of meeting each requirement for pedestrian access, but—due to human-neglect—is despotic for people outside of a motor vehicle.

My highest aspiration in making this video was that my fellow engineers would start to recognize the difference between a checklist approach and an actual design that considers humans. (I’ll admit I had some lower aspirations as well.) Not only has that not happened, but these continued responses just demonstrate the widespread human-neglect the profession suffers from.

Engineer: The DDI is pedestrian friendly.

Me: No, it’s actually despotic for humans that are not in a vehicle.

Engineer: You’re wrong. It increases traffic flow and there are fewer crashes per through movement.

This is silly, and it’s inane and unbecoming to suggest that I’m somehow wrong on this because it meets engineering metrics. Of course it does. I’ve never suggested it didn’t. In fact, let me state this clearly in the hopes that it will help some of you traffic engineers:

The DDI is a brilliant design if your goal is to improve traffic flow without increasing the width of the interchange. It will handle more vehicles-per-hour, especially during peak times, and it will do so with improvements to traffic safety. It can also be engineered to accommodate pedestrians in ways that are safer than non-DDI interchanges.

All of this is true, and I’ve never argued that it wasn’t. Here’s what else is true: the DDI is not pedestrian-friendly. Not in the least.

                Pedestrian: a person walking along a road or in a developed area

                Friendly: kind and pleasant

Jersey barriers, reflective markings, and decorative brick do not magically transform something so despotic into something kind and pleasant. They might make it slightly less despotic—and that’s arguable—but they do not make it friendly. If you want to argue with me on the DDI, if you want to laugh at me and claim I’m wrong, stop creating straw men to beat up, and instead make an argument as to why this interchange is kind and pleasant to someone on foot.

The sad thing is, I don’t think most of these engineers can, not because they are wrong—and they ARE wrong—but because they suffer from human-neglect. This affliction makes them incapable of even knowing they are wrong because they are not perceiving humans beyond the checklists they have created for themselves.

And these are the same people, with the same affliction, who are designing the stroads through our neighborhoods as well. We all deserve better.

Top photo from Don Kostelec.