The One Mile Super-Grid: Dallas’ Hidden Asset
This week's member blogroll article comes from Patrick Kennedy. It was originally published on D Magazine and is reprinted here with permission.
A sketch of the Washington DC street grid
One of the stories about how D.C. was originally designed has stuck with me since I first read about it. Pierre L’Enfant was hired by the fledgling U.S. government to design a city worthy of being the seat of government for the ambitious young country. L’Enfant, being a Frenchman, looked to the Baroque diagonal boulevards of Paris as a model. However, the D.C. we know today is different than his original plan.
Thomas Jefferson saw his plan and saw an over-reliance on hierarchy. It looked like class segregation by streets. The main boulevards were too dominant. Jefferson insisted on a plan that more closely resembled the organization of government as outlaid by the founding fathers, a representative democracy. The grand boulevards represented the “elected leaders,” so to speak, and pointed to the institutions of government, holding the pride of place. A hierarchy did exist by democratic process, but this hierarchy existed within a democratic framework as embodied by a very rigid orthogonal grid.
I bring up this story because I thought about it as I was sketching out an idea that you’ll see below, thinking about how to improve the transit system in Dallas. We don’t have a highly interconnected grid of streets and blocks outside the historic (pre WW2) areas, and those streets are often disconnected by post war highways and arterials. However, we do have a super-grid of arterials covering nearly the entire city, which presents both challenges and opportunities going forward.
The beauty of the super-grid system is similar to a regular grid in that every area of the city is connected to every other within one turning movement (theoretically). However, because it is on a one-mile grid, there remains the “last mile problem.” Except the last mile problem isn’t a problem for the drivers, which are given primacy on every single one of these arterials (rather than being “complete” and balancing modes of transportation).
Another weakness of the mile-grid superblock system is that the one square mile blocks nested within the super-grid funnel all traffic out to these arterials, often causing congestion with no parallel routes alleviating this congestion until you get another mile away. This raises the opportunity for transit to pick up the slack, particularly a frequent bus network, similar to the newly minted plan in Houston that is one of the few systems around the country gaining in bus ridership. The focus is on providing high quality service to all parts of the city, but understanding that transit can’t be everybody’s personal Uber. Transit does not work as well when it goes to “small destinations" like people’s homes and local streets.
What I’m showing below is how we can (theoretically) provide excellent bus service for most of the city by empowering the super-grid to connect the entire city. This began as a sketch in my notebook this morning and I put it into PowerPoint slides that are shown below since my handwriting can often be read by me and me alone:
Assume the above is one square mile area, typical of many parts of the city.
These one-square miles are set by the arterial system running past the perimeter of these blocks. These arterials are a mixed bag of “invaded” and “abandoned,” meaning they are either heavily congested or are significantly over-scaled or under-trafficked. Both of these conditions provide opportunities for transit improvements because many of them run for 10 miles or more, are fairly straight (as grids tend to be), and connect to many destinations (as well as other crossing arterials).
If we think about these arterials as potential frequent bus network routes, these would have buses running a maximum of 15 minutes between buses all day long. The connectivity and length of these super-grid arterials provide the built-in hierarchy so we don’t have to play winners and losers about where the majority of our bus resources go. Instead, they go to frequency and reliability, and thus service on these routes.
However, when thinking about the super-grid as the frequent network framework, I was worried about the quarter mile walking shed that attracts riders. i.e., if you have excellent service within a quarter mile, more people would be willing to walk or bike to frequent network. So I broke up the typical one-mile square super block into quarter mile squares, initially worried that coverage would suffer. But the math suggests otherwise…
If you can provide frequent networks on each of the arterials, that’s 8 of the 16 sub-squares that get a minimum of great (15-min.) service and 4 that would have exemplary service. Let’s say the times were staggered by 7.5 minutes. The corner sub-squares would have links running by every 7.5 minutes that could connect you to the entire city. As Jarrett Walker says, “This is what freedom looks like.”
Rather than worrying about serving one half of the city or the other half of the city, or how to serve 100% of the city equally poorly, we can serve 75% of the entire city with excellent transit service. That’s access to jobs, healthcare, schools, amenities, and everything else that comprises a city (provided other political barriers are broken down — transportation can only do so much).
The corner units, which have the best access currently (but only by car), would continue to have the best access but for all modes and thus all types of people. Since it has the best access (for cars) these areas are also the commercial corners and are thus destinations. They’re also designed for cars since the cross streets (the main and mains) serve only cars.
You can see these conditions existing in both North Dallas and South Dallas. Here is Forest and Preston:
Image from Google Maps
Here is Lake June and Masters in Pleasant Grove.
Image from Google Maps
What we can do by using the super-grid as the framework for a high quality bus network is begin to help the land use response to improved transportation in a strategic way. The market can begin to deliver greater mixed-use infill in these existing car-dependent retail zones. The public sector can look to strategically locate affordable and mixed-income housing along these routes and, rather than simply trying to shoehorn affordable housing where NIMBYs might react negatively (and not to accommodate NIMBYism), but to provide affordable housing where the greatest freedom is, where the greatest access to the rest of the city exists.
Real estate value is proportional to access. So much of the city lacks access beyond the reach of the car. Improving multi-modal access by utilizing the untapped resource of the arterial grid system allows us the chance to improve the arterials while revitalizing commercial nodes, and improving equitable transportation throughout the city.
If you’re still wondering why I invoked Jefferson and the L’Enfant plan of D.C., it is this. Let buses be the democracy, the meat and potato grid, serving the entire city, and the trains (which we can only afford so many of and which can go to only so many places) be the hierarchy.
(All images courtesy of D Magazine)
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About the author
Patrick Kennedy is founder and partner of Space Between Design Studio as well as founder of www.anewdallas.com and managing editor of Streetsmart.Dmagazine.com.
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