America has a 70-year tradition of 20 and 30-year plans. That’s fine for project programming, but bad for corridor preservation. What worked well enough for the last “horizon year” suddenly stops working in the next one. But by the time you realize “we could really use more through-streets, more multimodal paths, and more transit guideways,” haphazard development will have blocked off all your options. Thus the few corridors you have become overwhelmed, then super-sized into “Stroads and Big Dig freeways” in response.
Metro Analytics is pioneering techniques for “getting it right the first time,” as well as retrofit strategies for dealing with the mess that came from a lack of connectivity. NCHRP 19-14 is about right-sizing, and was led by Metro Analytics staff. In that, we describe a technique that has gained high visibility in Utah where we first tried it.
In ITE’s Transportation Planning Handbook, they describe the ideal macro-network spacing as an expressway or freeway every 5-miles, an arterial every 1-mile, and a collector every half-mile.
In Salt Lake County, the left is what they “should have had” and the right is what they actually have. Notice that the worst congestion in the state is where the grid is lacking both expressways and collector streets. What few streets exist are being widened to 5 and 7-lane “Stroads,” with not choice but to serve both regional and local mobility needs.
This graphic is used frequently by planners and leaders to make the case for doing a better job of connectivity in SL’s remaining Greenfields.
Application in Utah County
This “Scottish Plaid” comparison of what could have been to what actually is has proven to be a very popular graphic, used in presentations by Envision Utah, UDOT, the MPO’s, and many other agencies. Utah County has a lot of quickly urbanizing Greenfield land, and asked us to help them develop a “Buildout Grid.”
Their developed areas usually have at least a collector every half-mile. And because they are pinned in by mountains and a lake, they may never need as much arterial and expressway as these seems to suggest. But it is easy to see that they eventually will need a lot more than they’re currently planning on.
In this graphic, we applied “Grid Thinking” to create a “best fit” blend of existing with ideal. The majority of these corridors won’t be needed until after 2040, but unless the county acts soon to preserve them, they won’t be available when they are needed.
Identifying Level of Urgency for Preservation
This graphic shows which elements of the ideal build-out network are under the highest threat due to emerging development. “Highest threat” usually means that what is needed or funded by 2040 is something less than what is eventually needed. Thus the “eventual need” is not being actively preserved for, and fast development around that space means dozens if not hundreds of homes and businesses will block every path. Black paths need immediate attention, or they will be closed off as options, likely within a decade.
Spalding County, Georgia
Metro Analytics is leading a project in Spalding County, a “rural but urbanizing” county that is in the pathway of Atlanta’s expansion. It will likely take a very long time before it is fully urbanized, but if it ever does, it is easy to see their existing + planned network (middle) is woefully inadequate for anything close to build-out. Though still to be refined, the right-most diagram could end up being “what is possible” for preservation in the near-term. If their county commissioners and other leaders then work hard to require developers to “create continuity” in the general arterial and collector network, it may well be possible to have a reasonably adequate grid at build-out.
Graphics like this are an excellent way to quickly and visually discern how well your reality matches this ideal spacing (and if you’re like most, it won’t be very good). If it isn’t good, we know what to do! Place-Making Alternative Intersections, 8F transit, and other strategies will help a lot.
Also note, this is half-mile spacing, or a thru-street every 2,600 feet! Historic grids are much tighter than this – with a street of considerable length every 400-700 feet. Thus this recommendation is only for your macro-grid. Ideally your micro-grid would be even finer, especially in town centers and other activity centers with considerable emerging multi-modal potential.
Let Us Compare Your Situation to the Ideal
It is very easy to do this, and we are very fast at it. In not many hours, we can probably compare your city, county, or region to this ideal, and help you spot problem areas. We can also do a quick scan of opportunities to create better connectivity, and give you multi-modal project ideas (such as place-making innovative intersections) for addressing locations that cannot realistically increase macro-connectivity.