Transect mapping system created

Transect-based codes like the SmartCode provide new opportunities for municipalities to promote New Urbanism and smart growth. But the difficulty of applying these codes to local conditions remains a hurdle to widespread implementation. One method for overcoming that barrier is a system called TransectMap, which will soon be introduced. One of the challenges to using the SmartCode or other Transect-based codes is the difficulty of doing the local mapping of the Transect zones (T-zones). Especially in new growth areas, the process involves a fairly complicated balancing of T-zones. The balancing is needed because while, on the one hand, a Transect-based code aims to create town centers, neighborhoods, villages, and hamlets, on the other hand, developers need the flexibility to meet changing market demands. What’s a local planner to do — especially since the SmartCode by Duany Plater-Zyberk & Co. was recently put into the public domain, making its use more tempting? The answer devised by Criterion Planners of Portland, Oregon, is TransectMap, which can be used to map T-zones for general plans and for implementing Transect-based codes. Criterion will unveil the system — a step-by-step procedure for calibrating and delineating a Transect on local geography — at CNU XIII in Pasadena, California, in June. The method is meant to help planners tailor T-zones (core, center, general, suburban, rural, and natural areas) to local standards and map them so that they support growth visioning, comprehensive planning, and neighborhood design objectives. A set of instructions TransectMap is fairly complicated, but it does, for the first time, give planners a set of instructions. In much the same way that DPZ is distributing the SmartCode, Criterion is allowing individuals, organizations, and governments to use and reproduce TransectMap at no charge, provided they acknowledge Criterion’s copyright. “We’re interested in promoting more consideration of Transect principles in local planning, and drawing a local Transect map will help people better understand what the theory means on the ground in their community,” says Eliot Allen, Criterion principal. The method uses the SmartCode’s system of regional sectors, transect zones, and pedestrian sheds. These elements are integrated in a continuum that begins at the regional level and works down to block-level detailing of the pedestrian environment. Applying the method requires two preparatory steps: data assembly and calibration of Transect components. Data requirements include GIS files describing land uses, travel networks, and environmental resources. Calibration to fit local circumstances and preferences is done in 15 steps. Some of the steps involve defining objectives, such as deciding which land is to remain undeveloped. Other steps involve selecting dimensions, such as setting maximum walking distances for neighborhood destinations. The drawing of geographic boundaries starts with identifying six sectors on a regional-scale map. These sectors contain open spaces, existing urban neighborhoods, and locations for new development. The method allocates growth among the six sectors by asking the planners or other participants to decide: 1) what’s off the table (open spaces that will not be developed); 2) where to undertake infill development and redevelopment; and 3) where to place greenfield growth on the developable land that remains. The planners draw two open-space sectors (the “preserved” and “reserved” sectors) by mapping protected lands and critical environmental resource areas. They place the infill and redevelopment sector where the density of the street grid and the density of structures achieve recognized urban thresholds. For instance, the street-grid density threshold might be 12 miles of street (i.e., centerline miles) per square mile. The density of structures might be a floor-area ration of 0.35. greenfield categories The planners subdivide the remaining greenfield areas into three sectors: “intended,” “controlled,” and “restricted” growth. In a new community, the first priority is the intended-growth sector, which the planners delineate on the basis of proximity to high-capacity transportation facilities and major activity or employment centers. The second priority is the controlled-growth sector, which is placed near the remaining regional thoroughfares. The lowest priority for development is the restricted-growth sector, which contains developable land with limited transportation access. Next, the TransectMap method subdivides the sectors into Transect zones by considering walkability, environmental sensitivity, and regional transportation access. The planners delineate T-zones by relating the density of development to existing conditions. For example, T-zones of greater intensity are assigned to areas with high walkability, high regional accessibility, and low environmental sensitivity. This method also includes land area allocation goals that relate the T-zone intensities to the character of each sector. The infill/redevelopment sector, for instance, should be designated predominantly T-6 and T-5; a smaller portion of it might be designated T-4. The final step involves assembling and detailing the pedestrian sheds, generally on the basis of a five-minute walk. This step begins with identifying major pedestrian barriers, which create boundaries to the walkability of large districts. Inside the districts, the land is then subdivided into pedestrian sheds centered on neighborhood destinations, such as schools, parks, shops, and transit stops. Using previously calibrated walking distances and GIS travel networks, the planners draw pedestrian-shed boundaries around clusters of these destinations. Next they detail the pedestrian sheds at the block level. This includes fine-tuning the T-zone boundaries, designating civic and specialized functions, applying streetscaping standards, and delineating environmental protection features —wetland buffers and stormwater best management practices, for example. TransectMap can be downloaded from Criterion’s website at www.crit.com/documents/transect.pdf. It is also slated to be part of the upcoming SmartCode Manual. Eliot Allen and Andres Duany will present the new method at the CNU annual conference in Pasadena. Criterion considers the method a work in progress and welcomes comments at eliot@crit.com. u