A proposed interchange in Natick, Mass. is a classic example of greenwashing

The diverging diamond is an idea entirely given over to making things better for cars, and creates a disorienting, circuitous and dangerous world for pedestrians and cyclists.

The intersection of highways 9 and 27 in Natick Massachusetts, just east of Boston, is no urban wonderland.  It’s a classic American highway strip, with a line of car dealers (Dodge, Jeep, Volvo, and others),  the 9/27 mall has a “Stop and Shop” grocery store, but predictably turns its back on the intersection, and the roadways are ringed with acres of surface parking lots.

MassDOT, the state transportation agency is proposing the revamp the intersection, and one of their proposed designs is a “diverging diamond” interchange, that flips traffic to run on the left-hand side of two-way roadways, and creates an intricate weave of ramps that enables most vehicles to proceed through the intersection in almost any direction without stopping. A description of the project presented to the region’s metropolitan planning organization described the project in glowing “multimodal terms”

The modified interchange will include dedicated off-street facilities for pedestrians and cyclists, including a separate bike-ped bridge over Route 9 in between two spans that will support vehicular traffic. The enhanced shared-use facilities will improve connections to Natick Center and the nearby Cochituate Rail Trail.

Here’s the illustration of the diverging diamond proposed by MassDOT.  As you can see, its an intricate basket-weave of ramps, roadways and intersections.

To look at the illustration, you might get the impression that this is a kind of bucolic rural park, riven with pleasant walkways and filled with ambling pedestrians. There’s even a proposed separate pedestrian bridge running East-West across  Route 27.  Indeed, if you look closely at the rendering, it shows dozens and dozens of dots (presumably people walking) on pedestrian paths, sidewalks and crosswalks in and adjacent to the intersection.  If you count all the dots—and we did—the artist is conveying the impression that at any one time there are more than 110 people walking around or through this intersection.

Not only is that an absurdly large number—a quick perusal of Google streetview images shows no pedestrians on the current sidewalks and crosswalks in the area, and there’s precious little reason to believe that many people are walking from the U-haul or the Midas Muffler shop in the Southeast corner of the intersection to the Valvoline Oil Change shop or the Austin Liquor store in the Northeast Corner.

Current conditions at the intersection of Routes 9 & 27 in Natick (Google Streetview)

In truth, this is a profoundly pedestrian hostile design. The diverging diamond interchange flips the direction of traffic, so that cars are running on the left hand side of the roadway, creating deadly confusion for pedestrians used to seeing traffic on the right.  The basket-weave of ramps creates more conflicts for pedestrians, to cross from one side of route 27 to the other (even with the separate pedestrian overpass) requires people walking to negotiate at least six cross walks.  Between a lack of destinations, an environment swarming with cars going in every direction, and a lack of amenities, its hard to imagine anyone walking here.

While the project rendering creates the impression that the area will be chock-a-block with pedestrians, the rendering makes cars virtually disappear.  The illustration shows that once the project is built, routes 9 and 27 will be only lightly trafficked (one wonders why MassDOT is planning to spend anything on an intersection that’s so under-used).  We counted the number of cars, too–each red dot represents a vehicle. The illustration shows just 70 vehicles on routes 9 and 27, and on the myriad weaving ramps and connectors.

Red dots are vehicles, numerals are numbers of “pedestrian” dots in each block

If it’s really the case that about 50 percent more people are walking through this area at any given time than are driving, then maybe MassDOT should consider an entirely different design, one that prioritizes pedestrians.

But we know that all of the fictitious dot-people are just there to green-wash—or perhaps pedestrian-wash—what is in reality an entirely automobile-oriented project.  The illustration is a classic example of the kind of deception practiced by highway departments around the country, generating distorted and misleading renderings to create the illusion that they’re designing “pedestrian friendly infrastructure.

As we’ve discussed before, many of these projects are performative, or are simply automobile infrastructure masquerading as pedestrian infrastructure. Building remedial protections for pedestrians in hostile, vehicle dominated environments, with few or no walkable destinations doesn’t create walkable communities.

And diverging diamond intersections like this one are among the most inimical to pedestrians.  They’re designed with the purpose of speeding traffic and reducing or eliminating the number of times a driver must stop or yield at an intersection.  By creating the expectation that one can go faster, and stop or yield less, the intersections inherently make things more dangerous for pedestrians and for cyclists.

Our colleague Chuck Marohn at Strong Towns took a close look at arguments that the diverging diamond creates a pedestrian friendly setting. In his view, that’s a claim that would only fool a highway engineer. He’s got a video walk-through of a diverging diamond in Missouri that shows how hostile these intersections are to foot-traffic. His conclusion:  the diverging diamond is an “apostasy when it comes to pedestrians and pedestrian traffic.” His judgment is echoed by Schroeder’s study of diverging diamonds reports that vehicles accelerating to freeway speeds are unlikely to yield:



Bastian Schroeder, Ph.D., P.E. Director of Highway Systems, NC State University, Institute for Transportation Research and Education, Observations of Pedestrian Behavior and Facilities at Diverging Diamond Interchanges. (2015)

Editor’s Note:  A hat tip to Charles Denison IV, @cden4, for tweeting this gem.