The Transect

The rural-to-urban Transect is based on the idea that there is a place for everything in the human habitat. Where elements of the built environment are in their proper place, the whole is greater than the sum of its parts.

How does the Transect work?

Naturalists use a concept called the transect to describe the characteristics of ecosystems and the transition from one ecosystem to another. Andres Duany has applied this concept to human settlements, and since about 2000 this idea has permeated the thinking of new urbanists. The rural-to-urban Transect is divided into six zones: core (T6), center (T5), general urban (T4), sub-urban (T3), rural (T2), and natural (T1). The remaining category, Special District, applies to parts of the built environmental with specialty uses that do not fit into neighborhoods. Examples include power plants, airports, college campuses, and big-box power centers. The Transect is useful for designing and developing what Duany calls “immersive environments”: urban places in which the whole is greater than the sum of its parts.

Duany Plater-Zyberk & Company describes the concept thus: “The Transect arranges in useful order the elements of urbanism by classifying them from rural to urban. Every urban element finds a place within its continuum. For example, a street is more urban than a road, a curb more urban than a swale, a brick wall more urban than a wooden one, and an allee of trees more urban than a cluster. Even the character of streetlights can be assigned in the Transect according to the fabrication from cast iron (most urban), extruded pipe, or wood posts (most rural).”

Duany notes that every settlement has its own Transect, which can be studied and mastered. Each differs, to a degree, from all other Transects. For example, all downtowns have unique characteristics. Yet all downtowns have commonalities as well. The Transect concept flows from new urbanists’ observation of urban places, and a penchant for systematizing those observations. Transect zones form a patchwork across most communities. A common misconception is that the Transect implies a fried egg pattern from city center to edge. That’s only the case in small towns and villages, generally.

The Transect is a powerful tool new urbanists can use to analyze and understand urban places — and ultimately to design new settlements that will possess qualities associated with the best old urbanism. Because Transect zones can be described and defined, they are beginning to form the basis for a new generation of zoning codes responsive to human-scale needs and desires.

According to version 8.0 of the SmartCode & Manual (primary authors Duany, Sandy Sorlien, William Wright), the Transect “is evident in two ways: 1) it exists as place and 2) it evolves over time. As place, the six T-zones display more-or-less fixed identifiable characteristics. Yet the evolution of communities over time is the unseen element in urbanism. A hamlet may evolve into a village and then into a town, its T-zones increasing in density and intensity over a period of many years.”

The following section explains the Transect in some detail.

Urban core
The core (T6) is the densest and most urban part of the human environment. Many cities have only one core, often known as the downtown, although a large city like New York may have many cores. “It is the brightest, noisiest, most exciting part of the city,” notes the urban design firm PlaceMakers, in its pattern book for the TND called The Waters. “ ... with the city’s tallest buildings, busiest streets, and most variety.”

Many buildings in the core rise higher than four stories and typically include large office and workplace components. Buildings in the core are highly flexible in their uses — commonly mixing uses with shops and businesses on the first floor, and offices or residential units above. Most buildings are attached, with their fronts aligned. Full four-way intersections with rectilinear trajectories (i.e., streets at right angles to each other) are common.

The core is a focal point of activity and energy, benefiting from substantial traffic — both pedestrian and automotive. Good design allows pedestrians and automobiles to share the streets in a human-scale environment.

Setbacks in the core are generally zero to 10 feet. (Mixed-use buildings with retail on the first floor are built right up to the sidewalk.) Sidewalks are wide, generally 6 to 20 feet (the more urban the environment, the wider the sidewalk). Lot sizes vary, from a width of about 18 feet for some townhouses, to many times that for a large office or mixed-use building. The percentage of the lot coverage is generally high in the core.

Open space frequently takes the form of plazas. Transit service is the most frequent in the T6 zone. Housing mostly consists of apartments above retail, apartment and condominium buildings, townhouses, and lofts.

In the core, structured parking is the norm. On-street parking is also used widely. Thoroughfares are typically major commercial streets. Net residential densities typically range from 25 to more than 100 units per acre.

The center (T5) is like the core in many ways — buildings typically mix uses, with shops on the first floor and offices and residential units above, and are usually built to the sidewalk — but the character has more of a "main street" feel.

PlaceMakers describes the historical center thus: “The main street neighborhood was as diverse as any, including merchants living over their shops and old folks who didn’t want to have to saddle up to get to all the necessities. You could see lights on in the windows over the square every evening, and could hear mothers calling their kids to come in and do their homework ... .”

Most buildings are attached, with their fronts aligned. Full four-way intersections with rectilinear trajectories (i.e., streets at right angles to each other) are common. Buildings top out at two to four stories.

Setbacks are short and sidewalks are wide. Open space often takes the form of squares. Transit is often available. Housing consists of apartments above retail, stand-alone apartment buildings, townhouses, and live/work units (townhouses designed so that one or more floors can accommodate business activities). Unlike the core, the density allows for surface parking in the center of blocks. Thoroughfares generally consist of main streets and boulevards. Net residential densities generally range from 15 to 40 units/acre.

General urban

T4, general urban, is primarily residential, but still relatively urban in character. The streets have sidewalks on both sides, and they have raised curbs. Housing mostly consists of single homes, duplexes, townhouses, and accessory units. Small apartment buildings (up to about eight units) can be accommodated in the general urban zone if care is taken to design them to blend in with single homes.

Some businesses may locate in this zone — corner stores and cafes, for instance. Churches, schools, and other civic buildings also may appear here. Buildings in the general zone are not as large as those in the center. Open space takes the form of parks and greens.

Setbacks generally range from 5 to 25 feet. Many houses have porches, and the porches should be allowed to encroach into the setback zone. Lot widths for townhouses generally range from 18 to 30 feet, and for single homes from 30 to 70 feet. Lot lengths generally range from 80 to 130 feet. Rear lanes with garages and/or accessory units are common. Sidewalks should be 5 feet wide, ideally, to allow two people to walk side by side. Thoroughfares consist mostly of residential streets. Net residential densities generally range from 6 to 20 units/acre in this zone.

The sub-urban zone (T3) differs from conventional suburban development of the past 50 years. It hews closer to the character of early 20th-century US suburbs. Here’s how PlaceMakers describes it: “The sub-urban zone isn’t exactly the ‘burbs. It’s close, to be sure, but it doesn’t include some things like the big box retail you might instead find in a highway business district. The sub-urban zone is most similar to the areas on the outskirts of town where the town grid begins to give way to nature.”

Although sub-urban is the most residential zone, it can have some mix of uses — examples include civic buildings such as churches, schools, and community centers, and occasional stand-alone stores. The lots are larger, the streets crooked, and the curbs few. Plantings are informal. Setbacks from the street are larger than in the more urban zones, generally ranging from 20 to 40 feet. Porches are plentiful, and should be allowed to encroach on the setback. Lot widths usually range from 50 to 80 feet. Lots are often fairly deep in the sub-urban zone — ranging from 110 to 140 feet — to accommodate a larger backyard. Lots can range from 5,000 feet to a half-acre.

The sub-urban zone accommodates rear lanes, but it is also common to find front-loaded houses. (If the house is front-loaded, the garage should still be de-emphasized — set back from the front facade.) Thoroughfares consist mostly of residential streets that have a rural character. Of all the neighborhood areas, density is least in the sub-urban zone, ranging from 2 to 8 units per acre net.

Rural and natural zones
Beyond the neighborhood lie the rural (T2) and natural (T1) zones. The rural zone is countryside — where development may occur but where it may not be encouraged. “This is the quietest place you can find (except in a thunderstorm or a buffalo stampede), and it’s the place where the stars shine the brightest,” according to PlaceMakers.

Public infrastructure is sparse or nonexistent in the rural zone. The rural zone can be protected from development through mechanisms such as transfer of development rights, land banks, and agricultural zoning.

The natural zone includes parklands, wilderness areas, and areas of high environmental value (such as wetlands) that can withstand court challenges from developers. It includes all lands that have been permanently protected from development.

Special Districts
Special Districts (SDs) are urbanized areas that specialize in a particular activity. SDs are justified only when their uses cannot be accommodated within the other Transect zones. SDs may contain major transportation facilities such as airports and truck or bus depots, industrial areas, solid waste disposal and wastewater treatment facilities, hospitals, auto-oriented businesses like auto body shops, or even college campuses. SDs should, like neighborhoods, have a clear focus in their physical form. When possible and prudent, districts should be interconnected with adjacent neighborhoods to promote pedestrian access. SDs benefit from transit systems.

Although some are pedestrian-friendly (such as college campuses), SDs are the primary means new urbanists employ to accommodate uses that are inherently hostile to pedestrians. The idea is this: you can’t eliminate uses that are incompatible with human-scale neighborhoods — but you can concentrate these uses to minimize their damage. You can also place districts adjacent to walkable neighborhoods (if possible), lay them out in a modified grid, build sidewalks, plant street trees, and bring some of the buildings out to the sidewalk. These design elements ensure that, in time, districts are able to evolve into high-quality urban environments. In the meantime, walking is safe and the barriers to pedestrian activity are minimized.

Another technique new urbanists use for dealing with a pedestrian-hostile activity is the “B” street. Certain auto-oriented activities simply cannot coexist well with pedestrian activities. Therefore it’s sometimes best to make certain streets truly pedestrian-friendly — these are designated as “A” streets — and to concentrate auto-oriented activities on so-called B streets. Even within a high-quality street network, a B street can accommodate uses such as gas stations, muffler shops, and restaurants with drive-through lanes. A pair of A streets should run parallel to the B street, on both sides of it, to maintain a walkable environment. B streets can be thought of as districts that are one street wide.

From New Urbanism: Best Practices Guide.

For more information, visit The Center for Applied Transect Studies.



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