Chapter 1.1
Climate Change

• ALL
• Remove Code Barriers
• Create Incentives
• Fill Regulatory Gaps

Street Connectivity Minimums

INTRODUCTION

From ancient times to the mid-1900s, most city streets were built on dense, interconnected grids which were designed to prioritize convenient and direct access to places prior to the advent of cars.[1] This form of design can be seen in many urban cores, streetcar suburbs, and small towns across the country, where gridded street networks make for efficient, walkable networks well-suited for walking, bicycling, and public transit.[2] However, increased use of automobiles beginning in the 1920s and problems with overcrowding, congestion, and pollution in American cities gave rise to ideas of new developments with curvilinear streets in proto-pastoral settings, which were seen as cleaner and superior to contemporary urban areas. A hierarchy of streets, from busy highways and arterials to smaller collectors would lead to a detached house on a quiet street, preferably ending with a cul-de-sac to prevent through traffic.[3] Eventually, this curvilinear street form was given preference by the federal government.[4] Federal Housing Administration (FHA) guides explicitly characterized short blocks, grid networks, and mixed land uses (such as shops near houses) as “bad”, and winding, curving streets, set on suburban residential blocks of “up to 1,300 feet”, as “good”.[5] For reference, the American Planning Association notes that “the mean block length in San Francisco’s city center is 353 feet; in Lower Manhattan, 274 feet; and in areas of Boston built as of 1895, 190 feet”.[6]

Even as FHA guides recommended pedestrian pathways on longer blocks and nominally cautioned against dead-end streets, in practice following the FHA’s rules resulted in the creation of culs-de-sac and streets primarily designed for the circulation of automobile traffic rather than walking, and neighborhoods where peoples’ sense of direction was disoriented by the limited routes afforded by winding, curved streets.[7] (for our brief specifically addressing culs-de-sac and pedestrian movement see Pedestrian Connectivity through Culs-de-sac). Nevertheless, given the role that the FHA played in the development, funding, and insurance of new construction, developers were keen to follow its preferences, which were frequently codified into local regulations.[8] One source states that “from the 1950s until the late 1980s, there were almost no new housing developments in the U.S. built on a simple grid”.[9]

Reassessment of these suburban norms began to pick up pace in the 1990s, as core tenants of this thought began to be questioned.[10] Rather than calming or rationalizing traffic, the hierarchy of arterial, collector, and local streets reduced flexibility and increased strain on a small number of unsafe and congested thoroughfares.[11] Disconnected culs-de-sac far away from work or recreation impede peoples’ ability to walk and necessitate extensive driving; death and injury from additional driving negates any nominal safety benefit of living on a dead-end street.[12] Claims of escaping a crowded, polluted city to a pristine suburb are quickly negated by the increased emissions inherently associated with an automobile-dependent lifestyle.[13]

To this end, many municipalities have begun enacting ordinances mandating a minimum level of street connectivity in new developments or a maximum length to city blocks in an effort to push back against the norms of long, winding, disconnected streets and recreate a semblance of the interconnected street grids which are now prized in many older and traditional neighborhoods.[14]

The two approaches described below are the “block-length” approach and “connectivity index” approach. As the name suggests, a block-length approach mandates the maximum length of a street between intersections or the perimeter of a block.[15] A connectivity index approach requires new development to meet a minimum score on a “connectivity index”, which is calculated by dividing the number of street links over the sum of intersections and culs-de-sac; frequently described as nodes.[16] A third approach is the creation of pedestrian and bicycle paths between culs-de-sac, which provide a level of connectivity for pedestrians and bicyclists, mitigating the negative impacts on walkability (for more information on pedestrian and bicycle paths between culs-de-sac, see Pedestrian Connectivity through Culs-de-sac). [17] In addition to these strategies that calculate street connectivity, ordinances may also include explicit statements of purpose about promoting walkability, additional regulations concerning dead-end streets, and regulations concerning planning for traffic circulation among vehicles, bicycles, and pedestrians alike.[18] The following figures illustrate how different communities configure their schemes to increase mobility.

Figure 1, which is on file with the SDC (to view contact us at sustainablecitycode@gmail.com) shows connectivity index sample provided in the Cary, NC Code of Ordinances (further detailed in the “Additional Examples” section).

The ordinance provides that “[T]he measure of connectivity is the number of street links divided by the number of nodes. Nodes exist at street intersections as well as cul-de-sac heads. Links are the stretches of road that connect nodes. Stub outs shall also be considered as links. In this example, there are five (5) links (circles) and four (4) nodes (stars); therefore, the connectivity index is 1.25.”[19]

Figure 2, which is on file with the SDC (to view contact us at sustainablecitycode@gmail.com) shows connectivity index applied to a portion of the Northside neighborhood in Iowa City, Iowa; originally platted in 1839[20].

EFFECTS

Street connectivity ordinances guarantee a minimum level of access to and from destinations in a neighborhood. A well-designed and well-implemented street connectivity ordinance provides multiple direct routes to and from destinations, limits the construction of developments with few entry/exit points or connections to adjacent areas, and encourages more sustainable modes of transportation such as walking or bicycling over driving.[21] The tendency for people to create “desire paths” – impromptu flattened paths created by foot traffic in the absence of constructed paths – demonstrates peoples’ desire for direct access and convenience when on foot.[22] Time is frequently cited as a barrier in convincing people to walk more frequently to destinations; connected streets can reduce the time needed to walk or bicycle to places and thus encourage people to do more frequently.[23] More direct routes also means improved efficiency of public transit networks.

Case study modeling in Utah found that improving street connectivity by thirty percent increased walking by a factor of four to six times the prior frequency, and bicycling by four to twenty times over.[24] Each trip made by walking, bicycling, and transit means one less trip made by car; particularly of note given that transportation is now the single largest source of greenhouse gas emissions in the United States, largely from light-duty vehicles such as sedans, trucks, SUVs, and minivans.[25] The case study mentioned earlier found that the increase in bicycling and walking from a thirty percent increase on street connectivity would result in a five-hundred percent reduction in carbon dioxide emissions.[26]

Connected streets are also healthier and safer streets. Contrary to popular belief, an abundance of culs-de-sac and few intersections actually results in more dangerous streets as faster speeds are incentivized at the expense of non-drivers; it is the increased prevalence of intersections, pedestrians, bicyclists, and transit in better connected street systems which urges slower and more cautions driving.[27] A study of 24 California cities showed that places with better connected bicycle networks had a 10 to 17 times lower vehicle occupant crash fatality rate on average and a 3.8 to 4.5 times lower recorded vehicle occupant crash severe injury rate.[28]

Additionally, the ways in which connected streets promote active movement have direct impacts on health[29] Increasing physical activity can decrease the risk of excess weight, cardiovascular diseases, Type 2 diabetes, and certain cancers.[30] A study in the American Journal of Public Health found that walkable neighborhoods with good street connectivity reported an additional seventy minutes of physical activity and lower rates of obesity compared to residents of neighborhoods with poor walkability.[31]

Although much of this discussion has been focused on the benefits of connected streets, connected streets has benefits for drivers as well. The creation of multiple routes allows for alternatives pathways in the event of closures, and reduces traffic on arterial streets.[32] Emergency vehicle access is also improved with greater connectivity.[33] Overall, improved street connectivity is reduced with reductions in both travel times and vehicle miles traveled. Connected streets are also associated with more reliable public services as well. In snowy climates, areas without an abundance of culs-de-sac had a snowplow coverage area twice as large as their disconnected counterparts. Less driving also means reduced household costs for fuel and vehicle maintenance.[34]

EXAMPLES

Franklin, TN

Franklin calls for developments to “maximize the internal connectivity of the site wherever possible”, and to that end, establishes a maximum block perimeter of 2,400 feet in most circumstances ( e.g. six-hundred feet on any one side).[35] The absolute maximum block perimeter allowed under any circumstances is 3,200 feet, or eight-undred feet on each side, and only if certain criteria are met such as environmental or topographic constraints, street classification prevents a connection, or a proposed development contains an “internal parking structure.”[36] Culs-de-sac are similarly prohibited unless existing development or geographic conditions prevent a street connection.[37]

To view the provisions, see Franklin, TN Zoning Ordinance § 9.5.2 (2020).

Portland, OR

Portland, Oregon uses a block-length approach in setting connectivity standards in most residential and commercial settings.[38] Distance between through streets is generally set at a maximum of 530 feet, while pedestrian crossings are generally set at a maximum of 200 feet apart.[39] Alleys are also mentioned in this ordinance as a potential way in which to reduce the number of driveways and garage doors crossing sidewalks and facing streets, respectively (for our brief specifically addressing driveways and pedestrian mobility see Limit Driveway Access Points, and for our brief addressing drive-throughs see Prohibit or Limit the Use of Drive-Through Services). Additional direction is given to pedestrian connections, where it is stated that the end of a pedestrian pathway should be visible from its entrance point if possible, and that connections should take the most direct route possible.[40] Dead-end streets are generally limited to a length of 200 feet or less and providing access to 18 or fewer dwelling units.[41] Furthermore, unlike many other similar ordinances which exempt existing development to providing street connections, Portland’s Code states that “provision of through streets or pedestrian connections should take precedence over protection of existing dwelling units where the surrounding transportation system will be significantly affected if a new through street or pedestrian connection is not created”.[42]

Portland’s connectivity regulations are intended to “enhance direct movement by pedestrians, bicycles, and motor vehicles between destinations”, and that “[D]irect routes for bicycles and pedestrians from residential areas to neighborhood facilities, such as schools and parks, are particularly important to increase the convenience of travelling by foot or bicycle”.[43]

To view the provisions, see Portland, OR City Code ch. 33.654.110 (2018).

Lehi, UT

For all new residential developments with ten or more units, Lehi mandates a connectivity index of 1.5 to 1.8 and maximum block lengths of six-hundred to one-thousand feet depending on density, with denser developments requiring shorter blocks and higher street connectivity.[44] New nonresidential developments have a minimum connectivity index of 1.5 generally, 1.8 for mixed-use developments, and 2.0 for transit-oriented development (TOD).[45] Maximum block lengths for nonresidential developments range from four-hundred to one-thousand feet in areas zoned for manufacturing or mixed-uses.[46] All of this, including “bike and pedestrian circulation,” is to be provided in a circulation plan as part of a plat application.[47] To prevent the creation of isolated developments, stub connections must be built in new developments congruent to overall connectivity standards, and in turn must be connected to if or when new development takes place in areas where stubs provide connection paths.[48] Connectivity standards or block-length standards are generally loosened if trail connections are provided in addition to or in lieu of roadway connections.[49]

To view the provisions, see Lehi, Utah Municipal Code § 37.040 (2020).

ADDITIONAL EXAMPLES

American Planning Association, Model Streets Connectivity Standards Ordinance, p. 147, Chapter 4.11 (2009) (setting maximum block lengths at 660 feet, and prohibits gated communities).

PennDOT, Standalone Connectivity Model Ordinance, p. 33 (n d.) (setting a minimum link-node connectivity index of 1.2 to 1.6, a maximum block length of 400 to 600 feet, maximum street interval spacing of 660 feet, and mandates mid-block crosswalks on blocks longer than 400 feet).

Cary, NC Code of Ordinances § 7.10.3 (n.d.) (mandates a link-node connectivity index of 1.2 or greater for all new developments and requires culs-de-sac to be linked with a six-foot wide pedestrian trail if the connectivity index is modified).

Fort Collins, CO Land Use Code § 3.6.3 (2021) (setting a maximum distance between intersections at 660-1,320 feet depending on street capacity, prohibits gated communities, and requires development plans to “allow multi-modal access and multiple routes” to “neighborhood centers, parks, and schools” without the use of arterial streets).

ADDITIONAL RESOURCES

Utah Street Connectivity Guide, (2017), https://perma.cc/264B-7DVW.

Lehigh Valley Planning Commission, Street Connectivity Guide (2011), https://perma.cc/SQ2B-RDU2.