The Provision and Use of Active Transportation Networks in the Suburbs
- Author(s): Amos, David
- Advisor(s): Macdonald, Elizabeth
- et al.
Suburbs in the United States consist primarily of low-density, single-use residential subdivisions. These subdivisions also contain transportation networks that provide access to all of the homes. Throughout the past 70 years, these transportation networks have increasingly been designed to serve the automobile, at the expense of pedestrians and cyclists. The street networks are dendritic, sprouting cul-de-sacs from collector street branches (Southworth and Owens, 1993). This single-minded focus on auto-mobility has serious negative consequences for health, safety, sustainability, and equity. Countries with high levels of driving and low active transportation use are more obese than people in countries where the opposite is true, broadly speaking (Bassett et al., 2008). Car crashes kill tens of thousands of people each year in the United States. The transportation sector, particularly private vehicle use, is responsible for a quarter of global carbon dioxide emissions, and carbon dioxide is one of the primary contributors to global climate change (Howey, 2012). Cars generate air pollution that doesn’t just wreak havoc on our climate, but causes negative health effects that are disproportionately affecting low-income households, households least equipped to handle the associated costs, such as asthma treatment (Havard et al, 2009).
The alternative to suburbs designed for auto-mobility is one designed for a wider variety of transportation modes, including active transportation. Active transportation is a healthy and sustainable form of mobility that is only made better by a cohesive network of sidewalks, bike lanes, cycle tracks, off-street paths, and trails that provide a safe and comfortable place to walk and ride. These facilities are often not present in low-density suburban areas. There are several reasons for this, but one often overlooked reason is the role land use plans such as comprehensive plans, subdivision ordinances, and zoning codes play in the provision of active transportation infrastructure. This dissertation reflects on the history of off-street active transportation infrastructure in the suburbs, analyzes suburban street network design, and reveals how suburban shared-use path systems are designed and used. The conclusion provides recommendations for the design and regulation of suburban transportation networks that could result in more trips being made on foot or on a bike.
Chapter one provides a general overview of the literature common to each of the chapters. It begins by providing definitions to terms used throughout the dissertation but have contested meanings, including suburbs, active transportation, and walkability. The chapter continues by discussing the demographics of the suburbs and provides an overview of the literature on the transportation-land use connection. This connection is at the center of each subsequent chapter. Active transportation research is often siloed into different subtopics, such as health, sustainability, traffic safety, and equity. A brief overview of each of these literatures is provided. This section also serves as an introduction to the rest of the chapter, which explains why this research is impactful and relevant to planning practitioners today.
Chapter two traces the history of shared-use paths in suburban neighborhoods from the first appearance in Olmstead and Vaux’s Central Park through the interwar period, a significant time in the codification of suburban development patterns. The chapter ends with a discussion of Village Homes and its use of shared-use path design characteristics pioneered by earlier precedents. This history is told through the master plans, comprehensive plans, zoning codes, and subdivision regulations that enabled the construction of those paths, or did not enable them. The chapter points out that off-street paths appeared in influential garden city and garden suburb plans in the first part of the 20th century. They allowed for internal circulation within superblocks, large residential areas with cars pushed to the outside of the block. Off-street paths did not gain traction as developers rapidly constructed neighborhoods in the post-war era. The neighborhood unit concept, model subdivision ordinances, model zoning codes, and the institutionalization of street design engineering standards did not include recommendations to construct off-street paths. These plans all aimed to redesign urban form to accommodate the car. Off-street paths began to make a comeback at the end of the 20th century, as communities began to understand the negative externalities associated with designing cities exclusively for the car. This chapter contributes to the literature by providing a history of residential shared-use paths, something that has not been done before.
Chapter three continues the examination of neighborhood shared-use path systems, but with an eye to how they are designed and used in the present day. Three neighborhoods in the Sacramento area were selected for case study research on shared-use paths. These neighborhoods each have a local path system, but are not a part of a regional system. This chapter uses a pedestrian audit and survey of neighborhood residents to understand how people use neighborhood-scale shared-use path networks and how the design of such systems may affect use patterns. The results indicate that the paths are primarily used for recreation and not for making utility trips, such as commutes and shopping trips. Despite differences in the design of the path systems in the three neighborhoods, residents in each neighborhood reported the same general use patterns.
Chapter four considers the configuration of subdivision street patterns and their contribution to walkability and bikeability in the surburban context. Have suburban street patterns changed over time? Are they more walkable and bikeable now than they were in the 1950s? These questions are important to answer, and yet, have not been answered since the 1990s, and have not been answered on the scale of the subdivision. This chapter uses computational GIS methods to evaluate the change in subdivision street patterns over the course of decades, and at subdivisions of different sizes. This effort is greatly helped by the use of OSMnx, a tool for extracting and analyzing street patterns at any scale, including the subdivision. The chapter finds that while intersections and block sizes have trended toward increased connectivity over time, cul-de-sacs have increased in the 2000s and 2010s. Access points to the subdivision have stayed stubbornly low over several decades, despite their importance to creating a more regional active transportation network.
The conclusion chapter provides synthesis between the chapters and discusses the question: how can planners and real estate developers plan and design for suburban subdivisions that prioritize active transportation, given what we now know from this research? The chapter discusses how cohesive active transportation networks can be challenging to create when private communities limit access, the role subdivision ordinances and unified development ordinances can play in regulating the design of networks, and the potentially synergistic relationship between shared-use paths and public parks.
The conclusion ends with a list of best practices in the design of shared-use path systems and street networks. Those for shared-use path systems are based on the design characteristics identified in chapter two, but enriched by conclusions drawn from chapter three about resident behavior. The three key recommendations from this section are:
Design paths to be functional for commuters as well as recreational users. This can be achieved with wider paved surfaces, lines delineating traffic direction, and straighter paths.
Don’t design the park space to be overly wide, increasing trip length. The spaces should be wide enough to include shade-providing trees and a pleasant experience for those looking for a relaxing walk or bike ride.
Connect path systems to other land uses or path systems when possible. When no other uses or nearby paths exist, coordinate with the municipality to determine the best place for stub paths for future connections.
Those related to street network design concludes that access points to the subdivision is the most important metric to consider, as most people have to leave the single-use subdivision to reach another destination. Cul-de-sacs can be useful in subdivisions, but they are made better by connecting their ends to a shared-use path network that effectively creates a grid pattern for pedestrians and cyclists.