9 Sustainable Transportation

CHAPTER OVERVIEW

This chapter delves into the relationship between transportation and sustainability. It starts with an overview of what we mean by sustainability and its three interrelated pillars often referred to as the triple bottom line of environmental, economic, and social wellbeing and its relationship to sustainable transportation. It explores U.S. progress and challenges in achieving sustainable transportation from the perspective of transportation stakeholders at State DOTs, transportation’s impacts, and sustainable transportation indicators (STIs) as a key planning tool in sustainable transportation planning. It ends with sustainable mobility as an emerging technology-driven perspective redefining the policy discourse on sustainable transportation in the U.S. and abroad.

For a more comprehensive exploration of sustainable transportation, please refer to this textbook’s OERTransport companion: “Green Cities and Transportation,” available at https://uta.pressbooks.pub/oertgreentransport/, and “Sustainable Mobility,” available at https://uta.pressbooks.pub/sustainablemobility/.

CHAPTER TOPICS

1. What is Sustainability?
2. Progress Toward Sustainable Transportation in The U.S.
3. Impacts of Transportation
4. U.S. Sustainable Transportation Planning
5. Sustainable Mobility, Energy, and the Built Environment
6. Conclusion
7. Quiz
8. Glossary
9. Acronyms

LEARNING OBJECTIVES

Learning Objectives

• Summarize the three pillars of sustainability (social, environmental, economic) and their relevance to transportation.
• Identify, with examples, the environmental, social, and economic impacts of different transportation systems.
• Elaborate on the role of sustainable transportation indicators and challenges in gauging progress toward achieving sustainable transportation.
• Evaluate the role of public policies in promoting or hindering social equity within transportation systems.
• Summarize the policy phases of sustainable transportation in the U.S., up to this day.

INTRODUCTION

Transportation plays a crucial role in supporting a sustainable future for city residents. Sustainable transportation is an idea derived from sustainable development, a concept that was internationally shaped by the Brundtland Commission’s (1987) definition: “meeting the needs of the present without compromising the ability of future generations to meet their own needs” and the three-legged stool of sustainable development—economy, environment (or ecology), and social (equity). Although there is no universal definition of sustainable transportation, many have been offered, primarily in countries that have formulated national sustainable development policies. In the U.S., no such national framework exists. Still, initiatives by federal agencies such as the 2009-2016 partnership for Sustainable Communities between the US Department of Transportation (USDOT), the US Department of Housing and Urban Development (HUD), and the US Environmental Protection Agency (EPA) have represented significant federal coordination efforts for sustainable development.

Additionally, the National Cooperative Highway Research Program (NCHRP, 2014) published Report 750, “Sustainability as an Organizing Principle for Transportation Agencies,” and the Federal Highway Administration (FHWA) developed a “Transportation Planning for Sustainability Guidebook” (Amekudzi et al., 2011). The NCHRP report examined how transportation agencies could best support a sustainable society, while the FHWA guidebook defined sustainable transportation as “transportation that supports the sustainable development of the community that owns and uses the system.” (Amekudzi et al., 2011, p. 2), and emphasized that although sustainable development is the process for achieving sustainability, the two terms are typically used interchangeably. More recently, recognizing that transportation activities generate significant CO₂, air pollution, and greenhouse gas emissions, in the Fifth National Climate Assessment, the United States Department of Transportation (USDOT) highlighted investments and plans aimed at mitigating climate risks and reducing carbon emissions (USDOT, 2023), while it partnered with the U.S. Departments of Energy (DOE), Housing and Urban Development (HUD) and the Environmental Protection Agency (EPA) in launching a national initiative to decarbonize U.S. transportation in 2050.

This chapter first highlights sustainability and sustainable development concepts and then discusses how they relate to transportation sustainability policy and planning. It explores the challenges facing U.S. efforts to move beyond a “green transportation” stage, along with the emerging technology-driven sustainable mobility vision that redefines the current and future sustainable transportation policy and planning spheres.

WHAT IS SUSTAINABILITY?

Sustainable development is characterized by “growth that meets current needs without compromising the ability of future generations to meet their own needs” (Brundtland, 1987). This definition encompasses various complex frameworks, such as the triple bottom line (TBL), which considers people, planet, and profit, or equity, ecology, and economy, again following the three key pillars of social, environmental, and economic domains. These frameworks highlight the necessity of balancing conflicting objectives for genuine sustainability and can be represented in various ways (Figure 9.1). They emphasize that maintaining a stable society and a robust economy are essential for achieving ecological objectives such as carbon neutrality (Brundtland, G. H., 1987).

Following significant milestones such as the Brundtland Commission report and subsequent global efforts like the 1992 Earth Summit in Rio de Janeiro, Brazil, and the 2012 United Nations Conference on Sustainable Development (Rio+20), the United Nations adopted the Sustainable Development Goals (SDGs) through a resolution by the General Assembly in September 2015. These 17 goals acknowledge the interconnectedness of factors influencing sustainability (see Figure 9.2).

Media 9.1 The seventeen Sustainable Development Goals (SDGs). From United Nations. (2018, April 20). Do you know all 17 SDGs? [Video]. https://www.youtube.com/watch?v=0XTBYMfZyrM&t=3s In the public domain.

More recent efforts by cities, nations, and entities such as the European Union have tracked progress toward meeting the SDGs, as seen in Figure 9.2. According to this analysis, in the EU, there has been only moderate progress towards SDG 11, sustainable cities and communities, which includes target 11.2, affordable and sustainable transport systems. Out of 193 United Nations member countries, the U.S. ranks # 46 (score: 74.43), below Thailand at # 45 (score: 74.67) and above Argentina at #47 (score: 74.40). Finland ranks # 1 (score: 86.35) and South Sudan # 167 (score: 40.14), the lowest. A score of 100 indicates that all SDGs have been achieved in the Sustainable Development Report  (Sachs, et al., 2024).

Environmental Sustainability

Environmental sustainability entails the responsibility to preserve natural resources and manage global ecosystems to promote present and future health and well-being (Sustainability, 2022). Many principles relevant to transportation can be found in ecological science. For instance, nature operates on the principle that there is no waste – debris accumulates faster than biological systems can break it down, leading to pollution of air, water, and soil. Thus, systems that seem productive in the short term by meeting immediate human needs can ultimately harm broader natural systems and reduce future productivity.

Addressing limits in transportation requires various approaches:

• Energy inputs: Ensuring transportation energy comes from renewable sources.
• Street capacity: Adopting more space-efficient transportation methods when resources are limited.
• Finance: Ensuring adequate funding for creating and maintaining transportation infrastructure.
• Politics: Garnering widespread support for transportation initiatives (Brundtland, 1987).

The most influential cities worldwide offer diverse transportation options. While cities relying solely on human-powered transportation may possess charm, they may encounter economic challenges and isolation due to handling freight and long-distance travel limitations. Conversely, cities solely reliant on automotive mobility may experience short-term economic gains but are vulnerable to oil price fluctuations and resource constraints. Cities providing a range of transportation choices are more adaptable, enabling them to capitalize on economic trends while mitigating risks associated with overdependence on a single transportation mode.

Social Sustainability

Social sustainability entails actively promoting the ability of current and future generations to develop healthy and livable communities through both formal and informal processes, institutions, structures, and connections. Socially sustainable communities offer a decent standard of living and are characterized by democracy, egalitarianism, diversity, and inclusivity (Innovations, 2021). One way to represent the social sustainability framework is to consider the cultural, political, and economic domains, which can be conceptualized as recognition, representation, and distribution, respectively. (See Figure 9.4; Blue, Rosol, & Fast, 2019).

The direct impact of transportation systems and policies on social sustainability are not as easily measured as environmental and economic factors. Generally, initiatives towards social sustainability address some components of social progress, equity, or justice, and these may be measured through disaggregation for specific populations or indicators of the direction of change, such as poverty, accessibility, safety, quality of life, and housing. However, the quantification of social impacts across locations and populations is greatly constrained by the availability of appropriate data and the inclusion of these factors in models of transportation interventions. Ultimately, to more completely and accurately understand the transportation experiences may require qualitative analysis that directly engages with the people most socially impacted by transportation projects and policies (Lucas, et al., 2007).

Economic Sustainability

Economic sustainability involves developing strategies that ensure long-term financial prosperity for companies, countries, or communities while also considering environmental, social, and cultural factors. At the same time, a general awareness of business practices that contribute to climate change—such as burning fossil fuels or generating food waste—achieving true economic sustainability remains a significant challenge for many firms (Bish, 2021), communities, local governments, and transportation agencies today. Economic growth and efficiency have traditionally been prioritized over environmental protection and social equity. However, within a sustainability framework, economic sustainability factors must simultaneously account for economic systems’ external environmental and social equity costs.

In the realm of economic sustainability, the USDOT launched the “Ladders of Opportunity” initiative in 2014, which aimed to improve economic opportunities for underserved populations by connecting communities to economic opportunities through transportation infrastructure projects. This initiative sought to empower transportation leaders, grantees, and communities to enhance and expand workforce opportunities, helping lift Americans into the middle class (USDOT, 2016). While not explicitly framed in sustainability terms, the initiative was focused on addressing the equity and environmental externalities of past transportation decisions driven by economic growth imperatives, effectively seeking to “right” past “wrongs” (Coles, 2016).

Media 9.2 Bridging the divide: Connecting people to opportunity (USDOT 2016). https://www.youtube.com/watch?v=wh7I-j9MTpo

PROGRESS TOWARD SUSTAINABLE TRANSPORTATION IN THE U.S.

As previously noted, progress toward achieving the Sustainable Development Goals for transportation (SDG 11) has been moderate. This aligns with the Transportation Research Board’s (TRB, 2014) evaluation of U.S. transportation agencies’ efforts. TRB’s National Cooperative Highway Research Program (NCHRP) Report 750 endorsed the European Union Council of Ministers for Transport and Telecommunications’ definition of a sustainable transportation system shown in Box 9.1 (EUCMTT, 200).

Box 9.1 Sustainable transportation system.

A sustainable transportation system is one that (EUCMTT, 2001):

• Allows the basic access needs of individuals and societies to be met safely and in a manner consistent with human and ecosystem health, and with equity within and between generations.
• Is affordable, operates efficiently, offers choice of transport mode, and supports a vibrant economy.
• Limits emissions and waste within the planet’s ability to absorb them, minimizes consumption of non-renewable resources, limits consumption of renewable resources to the sustainable yield level, reuses and recycles its components, and minimizes the use of land and the production of noise.

This definition underscores sustainability as a goal of transportation policy systems.

The NCHRP report examined U.S. transportation agencies’ strategic challenges in advancing toward a sustainable transportation policy system that aligns with the triple bottom line (TBL) of environmental, economic, and social well-being. Recognizing that U.S. policy was beginning to address nonrenewable resources and climate change (albeit with varying government support), the report categorized the sustainability evolution of U.S. transportation systems into four models representing past, present, and future levels of transportation policy and agency actions (Table 9.1).

According to the analysis, most transportation agencies are positioned between Compliant Transportation (Level 1) and Green Transportation (Level 2). Many leading state agencies have moved beyond mere compliance with federal environmental mandates, implementing green initiatives such as advanced sustainability indicators, planning, and more inclusive policymaking. However, none have fully developed a Sustainable Transportation or TBL-focused policy system (Level 3). While some cities and international examples are pioneering Sustainable Transportation (Level 3), this is primarily in countries and cities with more direct control over land use.

Table 9.1 Transportation policy systems evolving toward sustainability.

Sustainability level	Period	Policy organizing focus	Transportation agencies
0	1950 – 1960	Safe Mobility: expand and support the mobility of people and goods. Economic growth and infrastructure expansion, no regard for environmental and social impacts. Focus on highways, mobility and suburban automobility	Develop mobility standards and performance measures
1	1970 – 1980	Compliant Transportation: balancing mobility with environment and economic development as required by law. Growing concern about air pollution, energy efficiency and environmental impacts. Clean Air Act (1970) and EPA established—transportation policy & regulations.	Comply with legal requirements.
2	1900 –2000	Green Transportation: more conscious incorporation of sustainable transportation (e.g., reducing transportation’s ecological footprint); reducing emission, expanding public transit and acceptance of social benefits but largely biased toward environmental “greening” and balancing environment vs. economic growth. Social equity and broader sustainability concerns not addressed.	Environmental considerations in planning processes; define “green” transportation planning, metrics, and delivery emphasizing environment over the other two TBL elements.
3	2010 –present	Sustainable Transportation: *increasingly supports sustainability’s TBL principle but reframed in terms of technology (smart mobility solutions) and decarbonization, US National Blueprint for Transportation Decarbonization.	*Agencies act on sustainable mobility solutions beyond “greening”, within funding constraints. Increased support for regional and local land-use & transportation planning
4	2050 –	Sustainable Society? *supports overall societal sustainability in terms of climate action: reducing GHG emissions to pre-2000 levels	*Delivers optimal mobility and accessibility resulting from balancing the TBL
Note: Table by authors based on TRB (2014), NCHRP Report 750. * Added by authors based on current trends; not in orginal report.

Insights from this TRB study highlight nine barriers for U.S. policy to move beyond “Level 2.” Currently, “greening transportation” dominates policy, planning, and practice in the U.S.

1. A strong pressure for economic growth and job creation at a time of declining federal transportation budgets.
2. Free markets and limited government views make it a difficult sale to the public and decision makers.
3. “Stewardship” rather than “sustainability” is more palatable to decision makers and planners.
4. Sustainability is taken to mean support for green or environmental programs.
5. The triple bottom line framework is narrow, neglects technology as a critical driver in achieving sustainability.
6. Climate change has been the driver behind state involvement in sustainability-related programs. The programs and plans are important because they energize planning at the intersection of environment and transportation requiring a multiagency and multijurisdictional planning approach.
7. Financial sustainability of transportation assets is a leading concern that trumps social sustainability concerns. Most DOTs focus on environmental justice (EJ) and context-sensitive solutions (CSS) in dealing with social concerns.
8. Sustainable transportation requires a more integrative and cooperative budgetary system, accounting for full social costs, and greater flexibility in resource allocation.
9. The evaluation of intergenerational and environmental justice, a big challenge in full social cost accounting.

As we shall see in the next sections, points 4, 5, and 6 are central to emerging directions in sustainable mobility, a technical and engineering perspective redefining the current vision of sustainable transportation.

IMPACTS OF TRANSPORTATION

Transportation is vital for cities and essential to people’s quality of life, yet it is also the largest source of greenhouse gas emissions, contributing significantly to global warming and climate change. Therefore, reducing transportation’s negative environmental, social, and economic impacts is critical for achieving sustainability. By applying a sustainability lens, we can better understand the broader impacts of transportation across the three pillars of sustainability—environmental, social, and economic (the triple bottom line or TBL)—and how they interact. Figure 9.6 illustrates the sustainable transportation goals within each domain, but true sustainable transportation considers the integrated impact of all three domains on each other.

Economic, social, and environmental domain interactions

First, consider the economic domain. Transportation is essential for economic growth, enhancing land value by increasing accessibility and mobility. Efficient transportation systems enable the smooth movement of goods, services, and people, fostering trade, commerce, and investment in urban areas. However, transportation efficiency is not just about these benefits; it also encompasses “the economic value and impact of transportation systems relative to the costs imposed on society and the environment” (Zheng et al., 2011, p. 21). Conventional economic analyses often overlook the environmental and social costs of transportation’s externalities. Without accounting for these, the true overall costs of transportation remain inaccurate, effectively subsidizing the system and distorting market signals. This inefficiency can harm both the economy and society, as seen in the case of prioritizing automobility, which imposes affordability burdens on lower-income households and increases greenhouse gas emissions, contributing to global warming (Zheng et al., 2011).

Transportation also significantly impacts social equity, which concerns the fair distribution of transportation benefits, as discussed in Chapter Four. Policies that prioritize private vehicle mobility can unintentionally disadvantage lower-income, carless populations. Similarly, transportation investments often benefit one community at the expense of another, such as when a new highway or bridge displaces a neighborhood. On the other hand, projects that enhance mobility and accessibility for older adults and individuals with disabilities can improve social equity by reducing barriers and expanding opportunities for these groups. From a sustainability perspective, the economic efficiency of transportation projects and policies must consider benefits and costs across all three economic, social, and environmental domains. This means evaluating not only the economic development benefits for households and businesses but also accounting for social equity and environmental impacts.

Next, consider the quality of life. Transportation profoundly influences residents’ quality of life through accessibility as highlighted in Chapter Six. It enables access to essential services and amenities, such as job centers, education, and healthcare facilities. Moreover, transportation infrastructure directly affects factors like traffic congestion, noise, and air pollution, all of which can significantly impact the well-being and satisfaction of city dwellers (Tessum et al., 2019).

Transportation policies can have a direct impact on public health, especially when they promote active transportation by funding walking and cycling infrastructure. Alternatively, focusing solely on motorized transportation can have negative effects. These policies not only influence public health but also affect quality of life and social equity, either positively or negatively. Moreover, new infrastructure projects can harm water quality in rivers and creeks, as well as biodiversity in natural areas due to runoff, necessitating environmental mitigation strategies like low-impact development (LID) (EPA, 2021), which also influences the economic domain.

Media 9.4 Disproportionate burden from air pollution. From Muijen, A. (2019, March 11). Black and Hispanic minorities in the U.S. bear a disproportionate burden from air pollution [Video]. (CC_BY). https://youtu.be/7S8CXEVjIh4?si=wwtCZZDQpb2g3vYi

In terms of environmental sustainability, the transportation sector is the largest contributor of US greenhouse gas (GHG) emissions. In 2022, according to the Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990–2022 (EPA 2024) (the national inventory that the U.S. prepares annually under the United Nations Framework Convention on Climate Change), transportation accounted for 37.4 % of total U.S. CO₂ emissions from fossil fuel combustion, and 28.4% of GHG emissions (Figures 9.6 and 9.7).

Transportation activities accounted for 37.4 percent of U.S. CO₂ emissions from fossil fuel combustion in 2022, with the largest contributors being light-duty trucks (36.8 percent), followed by medium- and heavy-duty trucks (23.0 percent) and passenger vehicles (20.6 percent). In terms of the overall trend from 1990 to 2022, total transportation CO₂ emissions increased due largely to increased demand for travel, which was a result of a confluence of factors including population growth, economic growth, urban sprawl, and low fuel prices during the beginning of this period. While an increased demand for travel has led to generally increasing CO₂ emissions since 1990, improvements in average new vehicle fuel economy since 2005 have slowed the rate of increase of CO₂ emissions. In 2022, petroleum-based products supplied 94.3 percent of the energy consumed for transportation, primarily from gasoline consumption in automobiles and other highway vehicles (51.9 percent) EPA, 2024, p. 46.

The carbon footprint of the transportation sector (Figures 9.8 and 9.9) is another indicator based on vehicle miles traveled (VMT) and passenger miles traveled (PMT) for the passenger transportation sector and per Ton-Mile for the freight sector, along with multiple transportation sustainability indicators proposed during the past two decades, for benchmarking and measuring the transportation system’s impacts on sustainability.

Consequently, transportation exerts a critical influence on the environmental domain of sustainability with well-known economic and social repercussions tied to climate change. Greening and decarbonizing the transportation sector has become a key strategy for many U.S. cities and states. For example, California has set a statutory goal to reduce greenhouse gas (GHG) emissions by at least 85% of 1990 levels and achieve carbon neutrality by 2045. With transportation accounting for about 50% of statewide GHG emissions—of which passenger vehicles contribute 71.5% (PCAP 224)—this sector is central to achieving these targets.

In summary, the economic, social, and environmental dimensions of transportation sustainability are deeply interconnected. The interplay among these domains highlights the complex interrelated nature of sustainability. Depending on the sustainability goals set by transportation agencies, and how they are defined, these interrelations are reflected in transportation sustainability objectives and measured through economic, environmental, and social indicators. These indicators gauge the system’s progress toward attaining the specified goals—a topic that will be explored in the next section.

U.S. SUSTAINABLE TRANSPORTATION PLANNING

At the beginning of this chapter, we referenced the USDOT’s Transportation Planning for Sustainability Guidebook definition of sustainable transportation as “transportation that supports the sustainable development of the community that owns and uses the system.” We also referred to a broader definition, provided by the European Union (Box 9.2). This definition is widely recognized as a comprehensive summary of the three domains of sustainability by institutions like the Centre for Sustainable Transportation at the University of Winnipeg (CST 2005), The Victoria Transport Policy Institute, Litman (2024), and other transportation experts and academics.

As mentioned earlier, this definition was adopted by the research team behind the TCHRP Report 750 as a framework of sustainable transportation. It was used in interviews with stakeholders from state and local transportation agencies to assess the U.S.’s progress toward achieving sustainable transportation.

Findings from TCHRP Report 750 address a frequently asked question: Is the current U.S. transportation system sustainable? Both academics and professional planners largely agree that it is not (Theis & Tomkin, 2015; Ramani et al., 2018; Ross, et al., 2020). This conclusion is supported by data, such as the billions of passenger miles traveled across various transportation modes, including local commutes and long-distance trips. As shown in Figure 9.10, automobile travel overwhelmingly dominates all other modes in the U.S.

Progress and challenges in sustainable transportation

TCHRP Report 750’s stakeholder interviews provided valuable insights into U.S. progress and challenges, particularly regarding policies, planning and programs for sustainable transportation from the practitioners’ perspective. Key findings include:

• Growing support for sustainability: Understanding and incorporating sustainability concepts in transportation policy is increasing, though some resistance remains.
• Complexity of sustainability: While awareness of sustainability is increasing, the concept’s complexity is often a barrier for decision-makers, and stakeholders may be hesitant to fully embrace it.
• Need for fiscal sustainability: In addition to economic, social, and environmental sustainability, a fourth domain—fiscal sustainability—is essential to ensure long-term funding for transportation systems.
• Challenges with social indicators: Developing comprehensive social indicators for sustainable transportation remains difficult, as economic and environmental indicators tend to be more robust than social ones. Agencies also face high costs and data challenges in creating in-house metrics.
• Organizational change: Transportation agencies must evolve their processes and culture to support the shift from green initiatives to true sustainability.
• One size will not fit all. Unique conditions of each state and locality require unique solutions, though tools and methods like indicators and scenario planning can provide useful assistance.
• Localities are the leaders in sustainability. TBL sustainability beyond “greening” initiatives can be best pursued at the local level. Significant progress has been achieved by a number of cities (Boston, Chicago, New York, San Francisco and Portland, OR). Localities have control over land use and revenue sources (user fees, local taxes) to support sustainability programs. In contrast, federal, state, and regional agencies face greater challenges at consensus-building for sustainability.
• Sustainability requires public and stakeholder engagement. Successful sustainability programs require stakeholder buy-in and meaningful public involvement.

These insights suggest that, apart from a few U.S. cities, persistent barriers related to fiscal constraints, organizational challenges, measurement difficulties, and limited public and stakeholder acceptance continue to hinder progress toward sustainable transportation policies at the state level.

Cities and sustainable transportation indicators (STI)

As mentioned earlier, because cities have more control of land use than transportation agencies, they are at the forefront of developing sustainable transportation indicators (STIs), which are widely supported for tracking progress toward specific sustainability goals. However, the success of these efforts has been mixed. Zhou (2012) reviewed STIs from eight authors and found that, while these indicators measured various impacts, most only partially captured the broader interrelated goals of sustainable transportation.

A more recent comprehensive review of 99 STI studies from North American (U.S. and Canada) European, Asian, and South American cities published by researchers between 2002 and 2019 (Karjalainen and Juhola, 2021) highlights significant variation in focus (e.g., travel modes, policies, plans, built environment, infrastructure, service and system performance), scale (project, neighborhood, city), methodology (quantitative, qualitative), and metrics. These differences, according to the authors, limit the ability to build cumulative knowledge and compare or widely implement these indicators in practice. However, their analysis shows that the most commonly used set of indicators are thematically related to GHG emissions, air pollutants, noise pollution, physical accessibility, land use, and accidents/fatalities (Table 9.2).

The studies analyzed reveal that many produced by academic researchers synthesize existing knowledge on STI, but few develop novel sustainable transportation frameworks with stakeholders as collaborators in indicator construction. Most focus on public transit and automobiles, with less attention to walking or biking. Methodologically, multiple-criteria decision analysis (MCDA) and modeling (as discussed in Chapter Three), Geographical Information Systems (GIS), participatory data collection and documentary analysis are commonly employed. The STI studies serve four main purposes:

• Identifying the most suitable indicators. These studies focus on the overall city’s transportation system and sustainable transportation associated with multidimensional concepts like livability, quality of life, and social vulnerability. They emphasize local context involving local planners and experts in the indicator identification and selection process.
• Assessing infrastructure and the built environment. These studies evaluate system performance across all modes at the city level, sometimes incorporating local planners, transportation experts, and Indigenous knowledge. Innovative sustainability scoring assessment frameworks are also applied from time to time.
• Evaluating policies and plans. Most studies focus on mobility modes at the city level, as well as at the district and project levels. MDCA is the preferred method of evaluation.
• Assessing citizen perceptions, satisfaction, and behavior. These studies typically evaluate city transportation modes, with some focusing on low-income neighborhoods. They all assess citizen perceptions, satisfaction or behavior using participatory data collection methods like surveys, focus groups, workshops, and social media, along with data mining and sentiment-analysis techniques.

There are significant shortcomings in STI research that highlight ongoing challenges in measuring and achieving progress (Karjalainen and Juhola, 202). These include:

• A persistent gap between the comprehensive conceptualization of sustainable transportation and its practical implementation, reflecting a mismatch between academic research and practice.
• Easy-to-measure aspects of sustainability, especially in quantitative indicators of social and socioeconomic conditions. For example, pollution exposure is often measured, while the benefits of physical activity are overlooked. Walking and cycling modes are rarely included, with automobiles and public transit dominating STIs.
• Cities often select indicators that present their performance in a favorable light, citing data availability as a reason for excluding more diverse or accurate measures. This distorts assessments and can mislead policy and planning decisions.
• Stakeholder involvement remains limited, and little progress has been made to address data availability challenges.

These challenges with sustainable transportation indicators (STI) align with studies examining the regulatory, technological, financial, organizational, and social barriers facing the transportation sector in its transition to sustainability (Jelti et al., 2023; Ross et al., 2020). However, a technology-driven sustainable transportation perspective, which emphasizes the climate crisis and the sector’s significant CO2 and other GHG emissions contribution to it, has been gaining prominence.

SUSTAINABLE MOBILITY, ENERGY, AND THE BUILT ENVIRONMENT

As noted earlier, for technologists and some transportation stakeholders, technology is often seen as the missing dimension in the traditional triple bottom line (TBL) of sustainable transportation. The concept of Sustainable Mobility has gained prominence, shifting the focus from simply vehicles and roads to a broader network of travelers, services, and environments. This approach leverages connectivity and automation to optimize mobility and improve energy efficiency (NREL, 2024), with the U.S. Department of Energy leading efforts to advance this vision.

Media 9.3 National Renewable Energy Laboratory (NREL) Sustainable Mobility: The transportation world beyond tomorrow is here today! https://www.youtube.com/watch?v=P_TH9ZuxX4o

This whole-system sustainable mobility approach uses the existing road infrastructure and focuses on maximizing energy savings by integrating electric vehicles, infrastructure, and automation to enhance both mobility and energy efficiency. It achieves this through:

Built environment connectivity and interaction: Connecting travelers, vehicles, the grid, and buildings to support trip choices, provide energy storage, and integrate transportation with the built environment. Electric vehicles (EVs) are used to balance electricity loads for buildings and utilities, supporting renewable energy. Learn more about vehicle-to-grid technology.

Vehicle automation controls: Enhancing energy efficiency, safety, and convenience through technologies like adaptive cruise control and truck platooning, which reduce drag, energy consumption, and traffic congestion. Explore platooning strategies from the National Renewable Energy Labratory.

Decision science: Understanding travel behavior and consumer choices to promote the adoption of fuel-efficient vehicles and energy-efficient travel choices.

Systems and modeling: Advanced research in smart mobility uses modeling tools and data resources, including webinars on decision science, connectivity, automation, multimodal travel, transportation electrification, and freight. Find more information about data tools from the National Renewable Energy Labratory.

By now, the reader may notice a strong convergence and similarities between this model and Smart City mobility solutions discussed in Chapter Seven. However, a key difference is that Smart City models are typically driven by IT companies, while this model is a federal government initiative intended to facilitate the former.

Sustainable mobility and environmental justice

The NREL’s technology and energy-driven approach anticipates rapid growth in electric vehicle (EV) adoption, necessitating a complete overhaul of charging infrastructures. To address environmental justice, their EVI-Equity Infrastructure Model focuses on improving accessibility for low-income, urban and rural, underserved, and underrepresented communities (Figure 9.11). This model employs high-resolution, comprehensive spatial analysis based on individual households in every U.S. census block group and incorporates a range of factors, including technological, behavioral, social, economic, environmental, and structural elements.

EVI-Equity assesses EV infrastructure at neighborhood, city, state, and national levels. It evaluates the historical development of justice and equity in existing EV and charging station networks and provides predictions and recommendations for more equitable future EV adoption and infrastructure deployment. Learn more about how EVI-Equity addresses accessibility and equity biases for underserved communities from the National Renewable Energy Laboratory.

Clean Cities: A collaborative for technology innovation

The USDOE’s sustainable mobility vision leverages a national technology collaborative that taps into local expertise, enabling the rapid diffusion, adoption, and deployment of mobility innovations. For over 30 years, the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) has sponsored the Clean Cities Coalition Network, which according to their mission, focuses on advancing technology to enhance the nation’s energy security, economic vitality, and quality of life.

This network operates under a loosely structured collaborative governance model that extends beyond the government’s formal structure. It engages private sector and civil society stakeholders, along with local, state, and federal government entities, in a range of ongoing collaborative projects and cooperative agreements. These efforts are supported by semi-autonomous local coalitions, covering areas that include about 90% of the U.S. population. (Figure 9.12) (Romero Lankao et al., 2023). Through these networks, USDOE labs crowdsource stakeholders’ ideas and civil society’s input into projects.

The U.S. Department of Energy’s laboratories, such as NREL, and its technology-driven sustainable mobility model—focused on sustainable fuels, clean-energy technologies and building the elements of a clean transportation infrastructure—have been collaborating with other federal departments and redefining sustainable transportation in terms of decarbonizing the transportation system.

Sustainable mobility and decarbonization

As introduced in Chapter 2, the United States has developed a blueprint for transportation decarbonization which is a joint effort of the Department of Energy (DOE), Department of Transportation (DOT), Environmental Protection Agency (EPA), and Department of Housing and Urban Development (HUD) to encourage strategies to reduce greenhouse emissions from the transportation sector by 2050 (2024). As shown in Figure 9.13, these strategies are designed to ensure that transportation is convenient (improving land use planning and community design for accessibility and walkability), efficient (expanding affordable, efficient, and reliable public transportation, ridesharing, MaaS, and rail), and clean (deploying zero-emission vehicles and fuels). The Blueprint will serve as the comprehensive plan for future policymaking, research, development, and deployment of the envisioned sustainable and equitable future of transportation in the United States. And will be followed with decarbonization action plans by the four departments in cooperation with state, regional, local and tribal entities, along with the private and nonprofit sectors. Learn more about the National Blueprint by reading the fact sheet, the full document, and the brief video from the U.S. Department of Energy.

Media 9.5 The U.S. National Blueprint for Transportation Decarbonization, U.S. Department of Energy (2023). https://www.youtube.com/watch?v=RKplZwqFwVk In the public domain.

While the U.S. National Blueprint does not explicitly mention Green New Deals (GNDs), it shares many similarities with them. GNDs are broad policy proposals aimed at addressing the climate crisis and economic inequality by investing in renewable energy, modernizing the energy grid, expanding public transportation, improving energy efficiency of the built environment, creating new jobs in clean energy industries, and addressing environmental justice (Figure 9.14). These GND proposals have been made both in the U.S. and internationally (Barbier 2009), with goals aligned to the Millennium Development Goals and aimed at spurring economic recovery after the 2009 Recession and the COVID-19 pandemic. In a broader sense, the Blueprint for decarbonizing the transportation sector could be seen as a GND for transportation.

A technology and engineering-driven approach to sustainable transportation may encounter fewer obstacles in today’s politically fractured and contentious environment. However, the social equity dimension of sustainability remains the most fragile and politically contested aspect of Green New Deals (GNDs) and public policy in both the U.S. and other countries (Green and Healy, 2022). As new climate policies evolve, mobility solutions that integrate technology with social justice goals are likely to gain broader public support (Bergquist et al., 2022). This approach has the potential to improve the U.S.’s performance in achieving Sustainable Development Goal (SDG) 13: Climate Action, where the U.S. currently lags behind many countries.

CONCLUSION

Transportation and sustainability are intertwined through the recognition of the need to address transportation’s negative environmental, economic, and social impacts. Ranked 46th among 167 UN member countries, the U.S. has much room for improvement in meeting the Sustainable Development Goals (SDGs). In terms of transportation, state Departments of Transportation (DOTs) have made progress since the 1950s and 1960s, moving from a stage of little concern for environmental and social impacts to the current “green transportation” phase, which emphasizes environmental and economic sustainability. However, they have not yet fully achieved the triple bottom line of sustainable transportation.

Several obstacles—financial, organizational, political, technological, and the lack of authority over land use (unlike cities)—have hindered further state-level progress beyond this “greening” phase. On the other hand, cities, apart from a few well-known leaders, often rely on sustainable transportation indicators (STIs) to measure progress. However, STIs face their own challenges, particularly in the social sustainability domain and the inclusion of active transportation modes, where data limitations are prevalent. Additionally, cities may sometimes select indicators that cast their performance in a more favorable light.

In response to the climate crisis, a technology and engineering vision of sustainable mobility and decarbonization is emerging, reshaping the U.S. sustainable transportation policy discourse—along the lines of New Green Deal proposals for post-pandemic economic recovery—focusing on a comprehensive transition to electric vehicles, renewable energy, zero-emission fuels, and increased automation. The U.S. National Blueprint for Transportation Decarbonization outlines a policy framework for modernizing and integrating the current road and electric grid networks creating opportunities for Smart City mobility solutions to integrate into this evolving landscape.

QUIZ

GLOSSARY

Acronyms

The Brundtland Commission, formally known as the World Commission on Environment and Development, and headed by Gro Harlem Brundtland, Norway’s prime minister, was convened by the United Nations in 1983. Its primary goal was to address the growing concern about the environmental and developmental challenges facing the world. In 1987, the commission dissolved and published “Our Common Future” or Brundtland Report, which defined and popularized the concept of sustainable development.

Carbon footprint: A carbon footprint (or greenhouse gas footprint) is a calculated value or index that makes it possible to compare the total amount of greenhouse gases that an activity, product, company or country adds to the atmosphere. Carbon footprints are usually reported in tonnes of emissions (CO2-equivalent) per unit of comparison (“Carbon footprint,” 2024).

Decarbonization: reduction or elimination of carbon dioxide emissions. Greenhouse gas (GHG) emissions due to human activity have been the dominant cause of observed climate change since the mid-20th century. There are many proven approaches for moving to a low-carbon economy, such as encouraging renewable energy transition, energy conservation, electrification of transportation (e.g. electric vehicles), and carbon capture and storage (“Low-carbon economy,” 2024).

Documentary Analysis:  a type of qualitative research in which documents are reviewed by the analyst to assess and code content into subjects, similar to interviews or focus groups (Documentary analysis, 2024).

Greening: Greening is the process of transforming living environments, and also artifacts such as a space, a lifestyle or a brand image, into a more environmentally friendly version (i.e. ‘greening your home’ or ‘greening your office’). The act of greening generally involves incorporating more environmentally friendly systems into one’s environment, such as the home, workplace, and general lifestyle. In a transportation context greening emphasizes biodiversity, reduction of land degradation, and climate change mitigation benefits (“Greening,” 2024).

Low Impact Development (LID) “refers to systems and practices that use or mimic natural processes that result in the infiltration, evapotranspiration or use of stormwater in order to protect water quality and associated aquatic habitat. EPA currently uses the term green infrastructure to refer to the management of wet weather flows that use these processes, and to refer to the patchwork of natural areas that provide habitat, flood protection, cleaner air and cleaner water. At both the site and regional scale, LID/GI practices aim to preserve, restore and create green space using soils, vegetation, and rainwater harvest techniques” EPA (2024) https://www.epa.gov/nps/nonpoint-source-urban-areas

Social Equity: justice and fairness in treating persons or creating and implementing governmental policy. (Ocean Science Trust, 2022)

Sustainability: a social goal for people to co-exist on Earth over a long time. Definitions of this term are disputed and have varied with literature, context, and time. Sustainability usually has three dimensions (or pillars): environmental, economic, and social.

Participatory Data Collection: a way for the population being studied and served to participate in research through the data collection process.

Public Health: the science and practice of avoiding illness, extending life, and promoting health through the coordinated efforts and conscious decisions of public and private organizations, communities, and people.

Sustainability indicators: Sustainability indicators and measurement are a set of frameworks or indicators used to measure how sustainable something is. This includes processes, products, services and businesses. Sustainability is difficult to quantify. To measure sustainability, frameworks and indicators consider environmental, social and economic domains (“Sustainability measurement,” 2024).

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