Straight-Line Radius v Shortest Path Analysis: Finding the right tool for the zoning code
One of the main barriers to mixing uses within a development is the ‘Zoning Tool’ used to determine how close preferred uses can be to undesirable or nuisance uses. Of course, one person’s preferred use can be undesirable to their neighbor. This is why having the right zoning tool for the context of the community is critical.
The two main tools used to separate uses are the Straight-Line Radius, often found in single use zoning codes embedded in Euclidean zoning ordinances that privilege single-family residential as the highest and best use, and Shortest Path Analysis, which takes a human scale perspective in separating uses and is often embedded in zones, districts and neighborhoods that are shaped by Form Based Codes.
Zoning laws in the United States have a long-standing history, that root in urban issues, and generated a framework for keeping industrial and commercial uses out of residential neighborhoods. While creating a precedent that gives preference to housing, it hard to argue with siting brick-makers and stinky glue factories in close proximity to residential dwellings. This change, of course, was mainly attributable to protecting homeowners in residential areas from devaluation by industrial and apartment uses.
The land use tool that is associated with a distinct separation of uses, often named ‘incompatible’ land uses, is the straight-line radius, which derives from the Supreme Court Case Village of Euclid v. Ambler Realty Co., 272 U.S. 365 (1926). This Supreme Court case established precedent for how a landowner may use their private property and divides communities into single use districts. The practice of dividing communities based on use, where usually only one use is allowed, is typically called ‘Euclidean’ Zoning.
This ideal is embedded in policy, typically through Euclidean zoning ordinances, that prioritize single-family residential as the ‘highest and best use’. To facilitate a transition between incompatible uses, Euclidean zoning ordinances have relied on the use of ‘buffers’ sandwiched in-between the incompatible uses. Enter the Straight Line Radius buffers.
In the case of buffers, usually one of two things happens, either a wholly desirable, noncontroversial use of land is placed between the two incompatible use types or a distance or 600 or 1,000 ft. is required to be kept between incompatible uses. Incidentally, the separation of uses is often associated with Suburban Sprawl and a myriad of other negative social issues that are often credited with prompting the New Urbanism movement.
Shortest Path Analysis
In considering how to better plan for places with a mix of uses, New Urbanism has developed an alternative zoning tool, the Shortest Path Analysis. Where the straight-line radius tool often ignores common typographical geographies, such as freeways or other environmental elements that provide physical barriers between incompatible uses, the Shortest Path Analysis is based on a human scale perspective measuring the separation distances of incompatible uses along a pedestrian path of travel.
The Shortest Path Analysis reflects pedestrians’ and bicyclists access to amenities and movement through the built environment, taking into account safety, convenience, and obstructions of movement. This in turn better predicts how pedestrians are likely to move through a business corridor and better aligns buffer distances between incompatible uses.
The shortest path analysis states walking distances must be measured along infrastructure that is safe and comfortable for pedestrian travel; including, public space e.g. sidewalks, all-weather-surface footpaths, crosswalks, or equivalent pedestrian facilities. The shortest path analysis does not include paths of travel that cross private property or roads that do not have safe and highly visible sidewalks.
Rural to Urban Transect
Both the Straight Line Radius and Shortest Path Analysis are perfectly acceptable planning tools to use to separate incompatible uses, when used in the right context. New Urbanists’ often point to the Rural to Urban Transect to determine what scale and density is appropriate to determine the form of the built environment. Often associated with Form Based Code, the transect is based on a series of zones that transition from untouched nature to the dense urban core of major cities.
Planning guru Dan Zack outlines how Form Based Codes can help promote compact development patterns, mixed land use, and a range of other benefits that are both supported by forward thinking General Plans and responsive to the context of place. Above is a graphic illustrating which Transect zones are appropriate for each of these zoning tools.
Of course, conflict occurs when determining the context of the use in question. Many jurisdictions around the State of California have updated their General Plan over the last decade to include design concepts such as, create Walkable neighborhoods, promote Transit Oriented Development, and incorporate a mix of uses, to which Urbanists rejoice. As noted Urban Designer Howard Blackson explains, in his Placemakers article “mixed-use makes for three-dimensional, pedestrian-oriented places that layer compatible land uses, public amenities, and utilities together at various scales and intensities.”
Unfortunately, when real estate developers or Entrepreneurs attempt to meet the General Plan vision, they all too often run into Euclidean zoning language emphasizing the separation of uses, rather than the mixing of them. The miss match between the Straight Line Radius tool used in a general urban zone, e.g. Business Districts, Mixed-Use Neighborhoods or Similar, is the inhibition of the full and equitable integration of mixed uses within a neighborhood.
This is incredible important when thinking about future economic drivers of local economies, such as Maker Spaces that include Digital Manufacturing (3D Printing, CNC Milling, Laser Engravers, Injection Molding etc.), Robotics (Design, Build and Code) or the emerging Cannabis industry.
Each of these uses play a role in the expanding importance of the Creative Economy and creating a Home Town Advantage. The danger is these and future uses are effectively ‘Zoned Out’ of many suitable locations simply because jurisdictions are applying the incorrect zoning tool Straight-Line Radius for the context, walkable neighborhoods and districts.
To foster the types of vibrant places that promote walkable, mixed-use neighborhood development, sustainable communities, and healthier living conditions, we must ensure we create policy strategies that offer flexible land uses that can transform a site from single use commercial buildings and parking lots into mixed-use village centers. To do this, we must make sure we are including Form Based Codes that use the Shortest Path Analysis when determining the distance between uses within Walkable Neighborhoods and Districts.
The commercial and retail environment is going through rapid changes. Creating a policy framework that expedites the process for innovation and new economies by aligning zoning code with shortest path analysis, when appropriate, will help.
Scott Watkins specializes in urban design at the intersection of environmental sustainability and behavioral economics. Scott views land use and development issues from the ground up, taking time to consider the human-scale interactions of space and place. Scott is a licensed California General Contractor, an accredited New Urbanist (CNUa) and LEED-ND professional. Scott holds a Bachelor of applied Arts and Science (BAS) in Public Administration, with an emphasis in City Planning, from San Diego State University and a Masters in Public Policy (MPP) and Masters in Business Administration (MBA) from Mills College.