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Kaid Benfield’s Blog

Virginia adopts innovative smart streets rules

Kaid Benfield

Posted March 23, 2009

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Under the leadership of governor Tim Kaine, the Commonwealth of Virginia has adopted new requirements designed to make neighborhood streets more connected, walkable, and safe.  In particular, the new regulations limit the number of new dead-end cul-de-sacs, require sidewalks in most new subdivisions, and encourage narrower street widths that slow traffic.  Developers must meet the new criteria in order for their streets to be eligible for maintenance by the state. 

Research shows that connected streets encourage walking and reduce vehicle miles traveled, associated emissions, traffic congestion, and emergency response times.  Moreover, as recounted here last month, new research shows that, contrary to popular belief, neighborhoods with connected streets have fewer traffic fatalities than do subdivisions dominated by cul-de-sacs.

Here's an illustration from the Virginia Department of Transportation showing how isolated subdivisions with dead-end streets make it difficult to reach even adjacent schools and shops without driving on frequently busy arterial roads:

  poorly connected streets limit mobility (by: Va DOT) 

It shows a hypothetical route marked in red to a neighbor's home, one marked in blue to a nearby school, and one marked in green to a nearby retail establishment.

In a story reported in Sunday's Washington Post, reporter Eric M. Weiss describes a situation typical of new development in many large metro areas:

"Recently, the Census Bureau reported that the longest average commute in the country was in suburban Washington: subdivisions off Linton Hall Road in Prince William, where [a family quoted in the story] live. Many of those communities were built using the cul-de-sac template, and traffic for all purposes is fed onto Linton Hall Road. Soon, the road was jammed day and night. Because of the state's dire financial straits, the county had to pick up the cost of widening Linton Hall to four lanes. traffic in Fairfax County, VA (by: NCreedplayer/Brian)And it is still jammed during peak times, with many trips just to get a gallon of milk or drop off children at school."

Although subdivisions with connected, gridded streets are gaining in the marketplace even without a regulatory assist, the pattern of dead-end streets has become so prevalent in new residential development that some consumers of new housing are distrustful of anything else.  Particularly for families with small children - a diminishing but still significant minority of all households - there is an understandable concern that connected streets will increase vehicle traffic and reduce safety. 

As noted, research suggests the opposite, and so does my personal experience with an older, traditional neighborhood.  In fact, even beyond my own neighborhood, as I rode my bike this afternoon through quiet suburban neighborhoods with connected streets, there were lots of happy children playing outside on a nice spring day and almost no automobile traffic.  It's largely a matter of design rather than restricted access.

For example, EPA's smart growth office had this to say about Northwest Landing (see photo), Northwest Landing (by: Michael Seidl, via new development in Washington state with a connected street network:

"The design of the streets and houses also encourages walking. Streets are narrow to slow traffic and make crossing easier. Lots are narrow and deep so pedestrians pass more of their neighbors during a given walk. Front porches are the focus of house designs so walkers can visit with neighbors as they pass. Garages are placed on back alleys so cars won't hit pedestrians as they back down their driveways."

It will be critical to build these design features into new, connected neighborhoods, to make new neighborhoods as inviting and well-functioning as possible, and to help win over the portion of the market that has grown accustomed to dead end streets.  For better or worse, though, there will remain plenty of cul-de-sac development in Virginia for the foreseeable future.  In addition to those already built, the new rules do not ban dead ends but do restrict their number, under a technical formula that varies the allowed number according to the type of subdivision in question. 

The deficiency in the market is in the smarter, more connected alternative that the Commonwealth is now promoting.  They are to be commended for it.

Smart growth policy wonks, go here for the actual regulation.

Kaid Benfield writes (almost) daily about community, development, and the environment.  For more posts, see his blog's home page. 


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Laurence AurbachMar 23 2009 05:10 PM

The VDOT system uses the "connectivity index" which is the ratio of street segments to intersections. Another way of thinking of it is the number of streets that run through the average intersection.

A neighborhood made entirely of intersections with two streets running through them will have a max connectivity index of 2. A neighborhood made entirely of 3-way intersections will have a max connectivity index of 1.5.

The VDOT regs use a minimum connectivity index of 1.6 in "compact" development; minimum of 1.4 in "suburban" development; and no minimum for "rural" development. All types have to provide multiple connections to other properties or streets in all directions, although there are no hard numbers associated with that requirement.

An interesting feature of the connectivity index is that it does not reference area. You could have a street layout with a high connectivity index with small, walkable blocks. You could have a street layout with a high connectivity index with giant, unwalkable superblocks. So the VDOT regs have another requirement, which is the block layout has to provide for reasonably direct pedestrian movement. There are no hard numbers for that either, and whether a development fulfills it or not will be up to the judgment of a VDOT administrator.

The VDOT regs do not ban cul-de-sacs; in fact they are basically neutral with respect to cul-de-sacs. The WaPo story got that part wrong. Cul-de-sacs are neither rewarded nor penalized in the connectivity index. In the overall regulation there are also plenty of exceptions and opportunities for variances from VDOT administrators.

Kaid @ NRDCMar 23 2009 05:35 PM

Thanks, LJ - those are very helpful additions. I admit that I found their index a little opaque and counter-intuitive in some ways, though useful - especially in conjunction with the narrow streets and sidewalks. It's a bold move by the Kaine administration.

George W BushMar 24 2009 06:48 PM

I don't understand all this gibberishness

Ian MacFarlaneMar 24 2009 07:07 PM

When I lived in Northern Virginia I always thought the state contributed to the terrible traffic by channeling all the rush hour traffic along a few major routes, which always became stop and go. This was worsened by residential streets that offered alternate routing being stoppered by speed bumps or barriers. This study bears those thoughts out. Now I live in St. Petersburg, FL; a city built mainly on a grid with lots of alternate ways to get from point A to point B. Much less traffic for a higher population to land ratio! However, that is changing as the city government is enamored with speed bumps and tries to block traffic and channel it into favored routes. You are trying to fix the problem and St. Pete is heading down the old, bad, path.

flinkMar 25 2009 03:24 AM

I at first thought this to be a stupid idea. When I've had the opportunity to live on a cul de sac, I appreciated the lessened traffic.

But after several years of dealing with cul de sac hell in southern california, banning them makes a lot of sense.

Kaid @ NRDCMar 25 2009 10:40 AM

Thanks so much for the perspectives. Keep working on it, Ian; it's an idea whose time has come.

Laurence AurbachMar 25 2009 04:36 PM

I was wrong about the treatment of cul-de-sacs in the regulations. Intersections are defined as a junction or a terminus, so cul-de-sacs do figure in the connectivity index. That means the regulations will work to reduce cul-de-sacs and the WaPo story was correct. Sorry for any confusion.

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