Roads
Virginia's new street connectivity regulations: the specifics
As mentioned Monday, new regulations in Virginia will prohibit residential subdivisions composed purely of culs de sac. Instead, the regulations will require that all new neighborhoods connect, or provide provisions to connect, to surrounding streets and properties.
In choosing to study this issue and ultimately promulgate new regulations, the Commonwealth has articulated that it expects a significant cost savings in the future for a variety of reasons. The change will divert public paving and plowing resources from de facto private, low-use roads to those that serve multiple uses. Localities should need fewer emergency facilities, as ambulances and fire companies can better reach farther locations with a better grid of streets. And more directly, it will reduce the pressure to construct additional inefficient roads, turning lanes, and streetlights at great expense.
A better connected street network will free residents from needing to drive on the few large arterials for every trip, as dwellers of exurban life frequently must do, even to go a half-mile to a friend's house in the next subdivision. It also will reduce the subsidy denser-living Virginia residents will have pay to allow others to live on streets that function as private roads for as few as three homes. Additionally, greater "back road" connectivity can generally provide safer options for cyclists off of higher-speed arterials.
Here are some of the specifics of the new regulations, and what they might mean going forward.
Background: In Virginia, as in many other places, the provision of subdivision roads generally sticks to the following process. First, the developer acquires a large parcel. Next, the developer drafts a "plat" showing how he will subdivide the parcel into lots and place the roads. The developer builds the roads, along with other infrastructure, such as storm drains. Finally, VDOT accepts the now-built roads into its "secondary system of highways."
This last step completely dedicates the roadway to the Commonwealth, eliminating any interest the developer once had in the roads, and shifting all future costs to VDOT. In Virginia, VDOT is ultimately responsible for the expensive maintenance and paving of roads it controls. The rules are slightly different in Arlington and Henrico Counties, but the concepts are similar.
Connectivity Index: Previously, while VDOT has had standards for the roads it would accept, including width and turning radius regulations, connectivity hasn't been part of the calculation. To incorporate this concern, the regulations introduce a planning concept called a "connectivity index" to compare various street network proposals. In Virginia's implementation, the number of street "segments" is divided by the number of street "intersections" to generate an index. The higher the ratio, the better. The trick is that culs de sac or any other street termini count as intersections. Meanwhile, "stub out" roads that dead-end at the parcel property line, for connection by other developers on the adjacent parcel later, don't count as intersections. This discourages the former and encourages the latter. For this reason, it might be better to refer to an "intersection" for calculation purposes instead as a "node".
For most population-heavy areas in the state, the required index going forward will be 1.6 segments per node. In less dense areas or projects (lots larger than half-acre or quite a distance outside of urbanized areas), the index drops to 1.4, while large-lot projects (over 2-acres apiece) in truly rural areas have no required connectivity index for acceptance.
Trumping NIMBYs: The road-dedication process is actually more complex than noted above. In reality, the project goes through an ever-lengthening series of negotiations and approvals along the way. Localities have the power to accept or reject subdivision plats, while VDOT gets to accept or reject road dedications (except in Arlington and Henrico, which control both themselves, arguably resulting in much better land planning).
Virginia foresaw that localities, under pressure from residents, might not agree to approve a subdivision plat that is designed to connect with the next project, forcing a road disconnect. If this happens, the regulations call for calculating the connectivity index as if the streets connected in their logical places, and then taking away sufficient amounts of the locality's transportation funds for VDOT to then construct the obvious connections itself. Thus, if a locality tries to block a road connection, it will fail, and then have to pay for the connection out of its own pocket.
The regulations allow for exceptions where there are physical barriers like railroad tracks or rivers, or where the adjacent parcels maintain "incompatible uses". However, in another forward-looking decision, the regulations specifically state that, "[i]n no instance shall any retail, office, or residential land use be considered incompatible land use with any proposed retail, office, or residential development." This explicitly prohibits localities or landowners from contesting a connection to an adjacent apartment complex or shopping center on the basis of "incompatibility".
Pedestrians are traffic too: In a shift from prior language, when road improvements take place, the new regulations require that "traffic, both vehicular and pedestrian, should be maintained ... until the new portion has been accepted."
For more information, there is a stakeholder presentation from December detailing many of these points and more, including new street-width guidelines.
This set of standards represents a refreshing sea change in road (and community) planning in Virginia. The Commonwealth deserves loud commendation for introducing this. To my knowledge, this is the first attempt by a state government, nationwide, to mandate such connectivity, shifting an approach that goes back decades. Unfortunately, though, I expect the practical benefit will be minimal in our region for the foreseeable future. It does nothing to resolve the lack of connectivity in existing middle- and outer-ring suburbs which will last for quite a while, extending up to 20 miles outside the Beltway. On the other hand, it will hopefully protect the communities surrounding the smaller cities and towns in the state, and could guide the redevelopment that may occur in Fairfax, Prince William, and Loudoun Counties fifty or a hundred years from now.
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by Froggie on Mar 26, 2009 10:37 am
by Joey on Mar 26, 2009 10:46 am
by Froggie on Mar 26, 2009 11:57 am
In any case, it wouldn't have much impact in the cities (or even Arlington), as they're largely built out (and built out with connected streets).
by Joey on Mar 26, 2009 12:03 pm
by Laurence Aurbach on Mar 26, 2009 12:06 pm
I would have liked to see bikes mentioned.
Otherwise: cheers to VA!
by Jasper on Mar 26, 2009 12:08 pm
by c5karl on Mar 26, 2009 12:09 pm
Even still, every state maintains interstate highways using federal dollars. Every state maintains its state roads. The state could simply say that the local jurisdiction must adopt the connectivity standards if they want to continue receiving maintenence on state roads running through their jurisdiction. It would be similar to how Congress imposed a national drinking age of 21: by tying adopting a 21 year old drinking age to road funds.
Thank you for analyzing this policy, Joey.
by Cavan on Mar 26, 2009 12:25 pm
Pavement is pavement. It's not going to cost significantly less to pave a road since the paving truck doesn't have to turn around in a cul de sac. Same for snow plows. And to the extent some roads will be used more, they'll require more frequent paving. All I see it doing is shifting costs around.
by ah on Mar 26, 2009 12:34 pm
yes- essentially they are trying to correct a wrong or set of wrongs- but it is 60 years too late.
by w on Mar 26, 2009 12:38 pm
by Cavan on Mar 26, 2009 12:46 pm
It also reduces the amount of design time for all components involved, and simplifies them, leading to far fewer change-orders or mistakes. I can go on forever, I am a big fan of grids.
by цarьchitect on Mar 26, 2009 1:42 pm
by RichardatCourthouse on Mar 26, 2009 1:55 pm
by NikolasM on Mar 26, 2009 6:44 pm
I wonder, though, whether the cul-de-sac system does avoid the problem we have in DC, which is everyone wants the "collector" road, or the cut-through road, or whatever you want to call it to be a street that's one or two over. Like the fight over the left turn prohibition from River Road to Fessenden Street (which gets repeated all over the place). At least in a cul-de-sac design, you know what you're getting when you buy--you're either on a back street or a main street, so you can't complain about a lot of traffic when you buy on the main street. Meanwhile, when there's a grid, it's much easier to demand (as a practical matter) that traffic be moved over one street.
by ah on Mar 26, 2009 9:13 pm
Non-proportional maintenance
The type of interconnections that we're talking about here (replacing cul-de-sacs) improve the utilization of less-than-busy residential roads per lane-mile constructed. Road maintenance is not purely a function of traffic, and some elements are completely unrelated.
More direct route
Interconnections which replace cul-de-sacs reduce the amount of VMT necessary for a given group of developments(we'll call it a neighborhood) to navigate its streets and the surrounding streets, saving on elements of maintenance which are proportional to VMT. This effect is particularly prominent if there is more than one major artery nearby (the neighborhood is not one-sided).
Internal pressure valve
Any neighborhood with multiple ways to get out and in is better off than one which (as has happened to me numerous times in my childhood home) can be cut off by a single car accident or downed tree.
External pressure valve
If the arteries surrounding a neighborhood seize up due to a traffic jam or accident, highly-interconnected neighborhood streets act as a bypass to ensure that everyone (both residents and through-traffic) can get beyond the obstruction safely. This may lead to a bit of traffic on the streets at times, but that replaces expensive construction of additional artery lanes, intrusive & expensive dedicated bypass roads like the ICC & Montrose Parkway East, and massive traffic jams which trap residents in their neighborhood and trap through travelers in a line outside it.
Services
All that have been mentioned are great, but I'd like to add one more. Bus Systems are forced to drive around subdivisions which rely on cul-de-sacs, rather than driving through them and picking up those inside.
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I'd like to raise one issue. While it's great that they've formalized a system... Correct me if I'm wrong, but it looks like it can still be gamed unless you have manual oversight for intent, and needs some additional constraints:

by Squalish on Mar 26, 2009 9:37 pm
by David Alpert on Mar 26, 2009 9:59 pm
by Squalish on Mar 26, 2009 10:19 pm
by Squalish on Mar 26, 2009 10:31 pm
Perhaps "No segment in the development may have a spot more than 2*(sqrt(area)) miles away from an entrance/exit to the development or a stub" would be more appropriate.
by Squalish on Mar 26, 2009 10:43 pm
Don't forget, developers don't care about gaming the system -- they care about making money. Arguably, they might think that would entail building culs de sac, but they'd certainly have no interest in developing a one-segment 5-mile maze (or some less exagerrated game).
It's not hard to develop a simple loophole to prevent connections to side parcels (a one-entrance one-road subdivision that loops around to intersect with itself near the entrance, with no other streets, produces an index of 2.0, under the Virginia model). But, it's very hard to build a lot of culs de sacs unless there are a lot of other intersections or parcel-edge stub-outs.
In truth, I think the biggest push may come from localities going forward. I think they'll see the writing on the wall from the state and will push, in their developer negotiations, to get connected plats. The new regulations might just be political cover.
by Joey on Mar 27, 2009 2:08 am
by Joey on Mar 27, 2009 2:11 am
by Froggie on Mar 27, 2009 6:45 am
Thanks
by Boots on Mar 27, 2009 9:04 am
by Joey on Mar 27, 2009 10:39 am
by Bo on Mar 30, 2009 2:19 pm
by Joey on Apr 6, 2009 11:05 am
by Dick on May 26, 2010 10:16 am
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