Developing Guidelines for Evaluating, Selecting, and Implementing Suburban Transit Services (2006)

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A-1 APPENDIX A: LAND USE This section defines suburban features in terms of three major themes (density, diversity, and design, plus adds a fourth, deterrents to driving) and sets the stage for a discussion of transit services that could successfully operate in environments with varying characteristics within each theme. In the context of transit service, contemporary suburbia is defined by the features that inhibit the provision of productive service. For example, previous research has identified a significant difference in productivity between bus routes in urban areas and those in suburban areas. Suburban routes frequently attract fewer than one-half as many boardings per hour as urban routes. Traditional urban transit services are characterized by fixed-route alignments and frequent all-day service. Such services are effective in areas where a sufficient number of travel markets combine, allowing one vehicle to serve the overlapping travel needs of a number of passengers and attracting sufficient ridership to justify frequent all-day service. In places where the traditional urban transit model has been applied without the presence of overlapping travel markets, most routes are far less productive or cost effective. Those qualities that contribute to high travel demand, and which suburban areas often lack, include: • Development Intensity: The more trip ends located within walking distance of a bus stop, the more potential passengers transit can draw, • Mix of Activities: The greater the variety of trip purposes that occur in the area served, the more likely that consistent, all-day ridership levels will materialize, and • Pedestrian Accessibility: The more comfortable an environment is for pedestrians, the more likely it is that potential passengers will choose to walk to a bus stop and use transit. These qualities correspond to the three main dimensions used to characterize land use, known as the “three D’s”: Density, Diversity and Design. Impediments to automobile use, such as parking costs and traffic congestion, constitute another feature that can increase the effectiveness of transit by making it more competitive with the private automobile. We will consider this a fourth “D” – Deterrents to driving. Each of these qualities, or features, has a continuum between the characteristics of the urban center and the rural countryside. For the purposes of this project, contemporary suburbia begins at the threshold that would not exhibit the qualities that support traditional urban transit service. Likewise, the threshold at which a place loses rural qualities establishes a lower bound for suburbia. While there has been a considerable amount of research on quantifying development patterns, creating an objective definition of contemporary suburbia in relation to these dimensions remains difficult due to variability from place to place. The following discussion summarizes the literature on this topic and presents some general thresholds at which communities transition from pedestrian-oriented and transit-friendly to automobile-oriented and transit challenged.

A-2 DENSITY Density is a widely used characteristic in transit planning because it is easy to compute from readily available data and it provides a broad indicator of how supportive of transit an area may be. Depending on the size of the land unit described by the source data, density can provide meaningful insight for planning at the regional, corridor, neighborhood, or station scales. Three commonly used densities are: • Residential density is frequently expressed in dwelling units per acre (gross or net). Gross residential density, typically used for regions or large parts of urban areas, expresses the number of households in an area of land that includes public uses, such as streets and open space. Net residential density is typically used for smaller areas such as neighborhoods or blocks. It is the number of households per acre of residential land, exclusive of streets and other common areas. • Employment density is frequently expressed as jobs per gross or net acre. Employment densities vary by the type of land use, with offices generally providing higher densities than retail, hotel, or industrial uses. • Floor-area ratio (FAR) is a measure of development intensity and building bulk that is computed by taking the ratio of the total building floor area and the area of the parcel on which the building sits. A two-story building that occupies one-half of its site has a FAR of 1.0. A five-story building that occupies its entire site has a FAR of 5.0. Regardless of which type of density is used it is important to remember that density is a proxy for what transportation professionals hope to capture – the number of trips that are induced by the area’s activities. DIVERSITY Many suburban areas include all of the same land-use types that urban areas include. However, decades of suburban zoning restrictions have created areas composed of larger patches of single uses than are typically seen in urban areas. The scale at which the mix of land uses occurs has an important effect on transit supportiveness. In urban areas, it is common to find residential, retail, educational, medical, and employment uses mixed in such a way that people can reach many of their daily destinations by walking a short distance. When there are so many reasons for people to walk, a high-quality pedestrian environment typically follows. This finely- grained mix of uses and pleasant walking environment encourages transit use, and accessing transit on foot, by placing many destinations within walking distance of bus stops. Researchers have developed various measures of land-use diversity, but the most common indices used in transportation planning do not yet capture the complexity of the interaction between uses. Landscape ecologists have developed techniques that show promise for urban planning in the way they evaluate the interactions between habitat areas of an ecosystem. One measure is the contagion index, which measures the total length of the edge shared by (i.e., the amount of exposure between) different uses. This index is able to measure the scale at which land-use variations occur in an area and can reflect different rates of trip generation between

A-3 adjoining uses. However, given that these techniques have only recently been introduced to the transportation-land-use field it is premature to include them in our methodology. For this study, an important criterion for rating land-use diversity is the distance one must travel to reach a reasonable balance of uses. Ewing defines a balanced mix of uses as having at least 20 percent residential development, at least 20 percent employment-related development, and at least 10 percent civic uses, such as parks, schools, and other public areas. Ideally, an area would achieve a balance between jobs and housing to maximize the amount of travel demand that can be satisfied within the neighborhood. The minimum radius of a circle that contains this balance between uses is a conceptual measure that can be used to distinguish suburban areas from urban and rural ones. DESIGN Site and building design are considerably different in areas that support traditional urban transit services than in areas where attracting riders is a greater challenge for transit. Suburban areas are characterized by sites with buildings set back farther from property lines than in urban areas. In many urban areas buildings are built to the street edge and up against each other. Large setbacks contribute to longer walking distances between bus stops and the destinations where passengers want to go. A by-product of larger setbacks is the discontinuity of the street wall, the edge created by buildings along the street. A continuous street wall is desirable in a good walking environment because it provides spatial definition for the street and provides a constant stream of changing views that enhances a pedestrian’s experience. Gaps for parking lots, vacant lots, open space, or buildings that are not oriented toward the street create greater gaps between activity and a less interesting, or even unpleasant, pedestrian environment. DETERRENTS TO DRIVING Urban areas frequently offer incentives to transit use in the form of disincentives to automobile use. Parking scarcity limits the availability of free parking, creates a market for paid parking, and thereby increases the cost of driving. These costs come in many forms: the cost of time spent searching for a space or walking from a distant location, or simply the parking fee. In addition, the concentration of activities generates traffic congestion which creates delays, reduces travel time reliability, and adds stress to the driving experience. Where these conditions exist, transit becomes an increasingly desirable alternative to the automobile for people who have a choice in how they travel. DEFINITION OF CONTEMPORARY SUBURBIA A place should exceed minimum thresholds for urban-ness on each of these dimensions – density, diversity, design, and deterrents to driving - to be appropriate for traditional urban transit services. Therefore, contemporary suburbia can be defined as places that do not meet urban standards for more than one of these dimensions. Because land-use patterns range from urban centers to rural countryside on each of these dimensions, it is necessary to define contemporary suburbia in terms of an upper threshold (above which traditional urban transit services are appropriate) and a lower threshold (below which purely demand-responsive rural services are appropriate). Because of the considerable variation from place to place and the presence of local complexities, finite thresholds are impossible to define. However, the following discussion presents insights derived from the

A-4 literature and it is reasonable to expect that localities will be able to define thresholds that reflect their unique environment. • Residential Density: Conditions in residential areas begin to discourage transit use when net densities fall below approximately 8 to 10 dwelling units per acre. Single-family detached houses on small lots, such as in the streetcar suburbs built before World War II, are commonly developed at this density. Neighborhood retail within walking distance of the majority of residents becomes infeasible below this density. The number of people within walking distance to transit stops also begins to diminish to the point that frequent service becomes infeasible. As the reasons for walking diminish, the provision of facilities for pedestrians, such as sidewalks, also begins to decline and many residential areas take the form of post-World War II subdivisions, with cul-de-sacs, parking- dominated site designs, and poorly connected street networks. Below ½ dwelling unit per acre (2-acre lots), residential areas take on a more rural character with large open spaces between buildings. • Employment Density: Below approximately 100 jobs per net acre, employment centers begin to exhibit features that discourage transit use, including large setbacks and surface parking. • Floor-Area Ratio: Below a FAR of 0.8 to 1.0, the incidence of suburban design features, such as low-rise buildings surrounded by open space, increases. Below a FAR of 0.1, places have very low densities common to rural areas. • Scale of Land-Use Mix: In typical urban areas, a reasonable mix of uses can be reached within a 0.H-mile radius of any point. In suburban areas, the need to travel a mile or more from one’s house to a reasonable selection of retail, school, or employment opportunities contributes to the automobile dependence that undermines transit use. A range between 1 and 4 miles for this measure is typical in contemporary suburbia. Rural residents must travel even greater distances, generally 5 or more miles, to reach typical destinations. • Building Setbacks: Most urban areas have setback lengths of less than 10 feet while suburban areas typically have setbacks greater than 20 feet. Many suburban retail strips have a setback of at least one row of parking (approximately 70 feet) between the street and the building. Rural setbacks are generally at least 50 feet from the highway. • Street wall Continuity: Urban street walls typically have no more than 40 percent gaps. Suburban areas typically fall in the range of 50 percent to 90 percent street wall porosity. Rural street walls rarely have any spatial definition, with gaps between uses generally exceeding 95 percent. When lower densities, larger setbacks, and large areas of free surface parking combine with high speed arterial streets and poor quality or non-existent sidewalks and crosswalks, suburban areas become much less walkable than urban areas. Since at least one end of a transit trip is usually made on foot, walkability is a key factor in the ability of transit services to attract riders. This characterization of suburbia moves beyond a jurisdictional definition. Older neighborhoods within the boundaries of traditional cities are gaining suburban qualities, such as auto-oriented retail development and lower density housing, while some suburban areas become more “city-like.” Wherever urban features exist, guidelines for designing urban transit services apply. However, if the combination of urban features are lacking, the guidelines from this

A-5 research, published separately as TCRP Report 116 (available online at http://trb.org/news/blurb_detail.asp?id=6525), can be used to identify which suburban transit services are most appropriate to provide service. TCRP Report 55 (available online at http://trb.org/news/blurb_detail.asp?id=2563) identified six types of suburban land-use environments based on their diversity of uses and how the intensity of their development (density) relates to that of the surrounding area. These environments included residential suburbs, balanced mixed-use suburbs, suburban campuses, edge cities, suburban corridors, and exurban corporate enclaves. Thinking back to the discussion of the activity surface, each topographical feature of the activity surface corresponds to one or more of these suburban environments: • Peaks represent the major activity centers, such as downtowns, shopping centers, edge cities, and community business districts. In a polycentric city, peaks have various heights based on their relative share of the region’s total residential, employment, commercial, medical, and recreational activity. Edge cities and downtowns of balanced mixed-use suburbs are examples of peaks. Peaks generally have urban characteristics – a diversity of uses, higher densities, and perhaps deterrents to driving. • Ridges represent the major travel corridors in a region. These corridors frequently connect peaks and are often lined with higher density residential, employment, or commercial uses. Suburban corridors are examples of ridges. Ridges have more suburban qualities – less diversity and design conditions where there are large gaps in the street wall, although there may well be deterrents to driving in the form of traffic congestion. • Points represent places in the region that are destinations for trips, but that do not necessarily fall on peaks or ridges. Suburban areas are characterized by a relatively high share of destinations that are not located within walking distance of other major activity centers or on major transportation corridors. Suburban campuses and exurban corporate enclaves are examples of points. Points are largely characteristic of suburbs, without the qualities of urban areas. • Plains represent the large areas of relatively low density residential, office or industrial development that frequently serve as one end of a trip. Residential suburbs are examples of plains. Again, plains are largely a phenomena of suburbia and do not have high diversity, density, design, or deterrents to driving. Although there are a number of ways in which to characterize suburbia, using the dimensions of diversity, density, design, and deterrents to driving can help communities place themselves in the spectrum of development patterns.