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Commuting, energy consumption, and the challenge of sustainable urban development
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ScienceDirect Commuting, energy consumption, and the challenge of sustainable urban development Ali Modarres This paper will provide an overview of the current state of knowledge regarding commute-related energy consumption patterns. Drawing from urban transportation and built environment literature, I will suggest the degree to which the job-housing imbalance, the geography of housing affordability, and the transportation infrastructure investment have produced heightened levels of energy consumption and inequitable urban environments.
Address Urban Studies, University of Washington Tacoma, United States Corresponding author: Modarres, Ali ([email protected])
Current Opinion in Environmental Sustainability 2017, 25:1–7 This review comes from a themed issue on Sustainability challenges Edited by Chiho Watanabe, Steffen Loft, Pengjun Zhao and Tony Capon Received: 04 October 2016; Revised: 17 January 2017; Accepted: 20 January 2017
http://dx.doi.org/10.1016/j.cosust.2017.01.011 1877-3435/ã 2017 Elsevier B.V. All rights reserved.
Introduction The relationship between transportation and energy consumption has been investigated extensively. Over the last few decades, particularly after the 1973 oil embargo, a significant body of literature has engaged with this topic to either advocate for reduction in oil dependency and air pollution [1,2,3–6] or argue for further implementation of transportation demand management [7] and sustainable mobility policies [8] that reduce vehicle miles travelled, and by default, reduce auto and fossil fuel dependencies. Regardless of their perspectives, research on commute-related energy consumption patterns has largely concerned itself with the urban form, job-housing balance, and overall urban mobility patterns (e.g., [9–19], which are the main topics of the larger transportation planning literature. While the relationship between density and planning has been more regularly explored (e.g., [20–22], a growing literature is paying closer attention to the nuanced relationship between density, energy consumption and affordable housing (e.g., [23]. This literature www.sciencedirect.com
points to the trade-offs that occur when multiple public goods are simultaneously considered, suggesting that sustainable development may demand more rigorous attention to equity issues, particularly when central cities become successful hubs for economic and real estate development. In this paper, a summary of this research will be presented, arguing that a more comprehensive debate may be needed to fully consider some of the driving factors that extend the residential geography of our cities. This includes housing affordability in highly dense but unaffordable cities, such as San Francisco or Seattle, where a significant number of low to middle income employees must commute long distances to access relatively affordable housing markets. Within this research arena, the role of transportation infrastructure and the geography of major job centers cannot be ignored.
Energy consumption, urban form, and equity While transportation planning gradually shifted its attention from mobility to accessibility, promoting higher urban densities, transit, and non-motorized modes of commuting to work, there does not appear to be a universal agreement about whether the promoted strategies produce the expected results or affect different sectors of society equally. As early as the 1980s, scholars had connected the urban form to energy consumption (e. g., [6]. A few years later, Newman and Kenworthy [24] provided the foundation for comprehensively connecting commuting-related energy consumption patterns with the urban form and land use planning. This was followed by an international comparative study [25] which, among other things, recommended increasing the cost of auto ownership and use. This was due to the fact that “as density increases, both car ownership and use decline” (p. 712). This line of argument, backed by empirical evidence, albeit measured at different spatial scales and localities, has been strengthened by additional research (e.g., [26,27,28,18,29,30]. In response to the emerging debates, Burgalassi and Luzzati [31] illustrated that while there is a relationship between CO2 emission and density, “polycentriciy alone does not reduce emissions” (p. 144). Contrary to this finding, research by Yin et al. [32] suggests that a polycentric urban structure may be a better choice for compact development, and Zhang et al. [33] found that as a metropolitan area goes through various stages of development, including the appearance of new employment centers, commuting patterns and the experience of some suburbs positively Current Opinion in Environmental Sustainability 2017, 25:1–7
2 Sustainability challenges
improves, resulting in less energy consumption. Wang et al. [34] go further by illustrating how land use intensity and higher population densities contribute to higher local production of CO2 emissions. This study expanded the scope of research beyond transportation to highlight the dilemma of focusing entirely on one aspect of urban planning to proscribe or advocate for a specific urban form. However, by focusing just on transportation, Mindali et al. [35] challenged the notion that there is a simple relationship between urban form and energy consumption. Feng et al. [36], Aguilera and Voisin [2], Lo [37], Larson and Yezer [38], Lin and Du [39], Yang et al. [40], Brand et al. [3], Clark [23], Lovelace and Philips [41], Modarres [16], Liu and Shen [42], Brand and Preston [4], and Boussauw and Witlox [48] have also challenged the primacy of density in determining commuting patterns and energy consumption by addressing the nuances of who actually benefits from density, as well as commuters’ socioeconomic characteristics, gender, and patterns of automobile ownership. The findings of this body of work highlight the importance of equity and the uneven nature of most metropolitan regions. While normative assumptions about how and where we should live abound, our collective realities point to more limited choices in housing and job locations. Land value structures affect our urban social geography [43] and cannot be ignored when discussing transportation and equitable approaches to improving either mobility or accessibility. Litman [44] offers an alternative approach for mitigating auto-dependency and energy consumption by evaluating various market intervention techniques, for example, increasing fuel excise taxes, and applying new technologies, such as more efficient fuel consumption, against mobility management strategies. Through a comprehensive analysis, he concludes that the latter produce a more positive result without creating social inequities. Litman’s attention to the issue of equity is somewhat rare in earlier debates regarding the importance of the urban form in transportation planning, particularly as it relates to energy consumption. The sustainability framework that included an equity dimension to environmental and economic considerations elevated attention to this concept further. For example, Dujardin et al. [11] argue that the density solution should be viewed as a part of the picture, allowing us to consider issues of equity in urban, peri-urban and rural conditions. Their research suggests that “better-than-average performance” can be found in all types of settlements, suggesting that the way forward may be to redirect economic development and job creation in places with limited access to them. Through examining socioeconomic status and transportation behavior, Kotval and Vojnovic [45] point to the importance of class as it relates to mode choice, distance travelled, and level of energy consumption. Their findings suggest that “the highest-income grouping consumes 3.4 times the annual fuel . . . and emits 3.8 times the Current Opinion in Environmental Sustainability 2017, 25:1–7
carbon monoxide . . . than the lowest-income grouping” (p. 93) in urban Detroit neighborhoods (which excludes compact and dispersed suburbs).
Urban form, commuting and housing affordability An important aspect of commuting patterns in larger metropolitan areas is housing affordability [43], which appears to be highly correlated with population density [23]. In other words, as urban core density increases, housing affordability is diminished, pushing middle and lower income populations further away. As such, a portion of the workforce pays more for transportation in order to afford housing. Cities such as New York, San Francisco, and Seattle are highly dense and unaffordable at their cores, while relying on a large number of workers who cannot compete for housing close to work. While jobhousing indicators may illustrate a reasonable ratio, it is important to realize how many people, particularly office staff, public sector employers, and service industry workers who cater to the higher income population, must commute long distances to work. As such, these cities create a spatially-extensive commuter-shed, largely shaped by housing consumers’ attempts to achieve an optimal combination of housing and transportation costs. Under such scenarios, reliance on cars and transportation infrastructure becomes necessary. It is for that reason that Mattingly and Morrissey [46] ask that we combine the cost of housing and transportation to understand the geography of affordability in a metropolitan region. Islao et al. [47] used this Housing and Transportation Affordability Index in a city in Iran, showing that some suburban residents pay 57% of their income for transportation and housing, whereas the ideal figure is 45%. Given the importance of equity in sustainable urban development, it is crucial to acknowledge the impact of housing affordability when promoting even higher densities in urban cores. A metropolitan area cannot be sustainable if a significant portion of its blue and white collar workers must commute long distances to work in highly concentrated workplaces in central cities. In the remainder of this paper, I will explore the more recent data on four counties in the Pacific Northwest of the U.S., where Seattle is located, to illustrate the complexity of the transportation environment and its associated housing affordability dynamics. The counties of Snohomish, Pierce, Kitsap, and King, where Seattle is located, house nearly 3.9 million residents. Over the last two decades, Seattle and its neighboring cities of Bellevue and Renton have become magnets for technology companies, online services, and other employers in finance, real estate, and insurance sectors. This agglomeration, within a small geography, has generated a significant presence of service sector jobs, as well as competition for housing, which in turn has increased the cost of housing (see Figure 1) and generated a www.sciencedirect.com
Commuting, energy consumption, and sustainable urban development Modarres
3
Figure 1
Median home value.
significant worsening of congestion in the region (i.e., particularly to and from Seattle). According to the U.S. Department of Transportation’s Federal Highway Administration (FHWA), by April 2015, congested hours in Seattle reached 6:38 hours, which was slightly higher than the previous year.1 Seattle was, in fact, among the seven major cities whose congestion indexes worsened in all three measurements calculated by FHWA. In other words, as Seattle’s central core has densified (as have portions of Bellevue, Renton, and Kirkland, all located along the eastern shores of Washington Lake), the cost of 1
Urban Congestion report, retrieved October 2, 2016 http://www.ops. fhwa.dot.gov/perf_measurement/ucr/reports/fy2015_q3.htm. www.sciencedirect.com
housing in these regions has moved out of the reach of many employees, and average travel times have increased. Comparing Figure 2 with Figure 1 suggests the ironic outcome. Where housing is at its highest value, average travel times are lower. These are places where high-paying jobs have matched the housing density and values. However, along the I-5 corridor and other areas where incomes are lower and housing more affordable, average travel times are larger. Table 1 reports average travel times by median home value. While census tracts in the lowest category (i.e., below $20 000) report an average travel time of 26.7 min, the second lowest category ($200 000–$299 999), which occurs in 303 tracts or 41% of all tracts in the four counties, has the largest reported Current Opinion in Environmental Sustainability 2017, 25:1–7
4 Sustainability challenges
Figure 2
Average travel time.
Table 1 Relationship between average travel time and median home values Home values
Average travel time (min)
No. of census tracts
Std. deviation
Less than $200,000 $200 000–$299 999 $300 000–$399 999 $400 000–$499 999 $500 000 or higher Total
26.7 29.8 29.0 27.0 26.0 28.4
113 303 173 97 87 773
6.5 4.7 4.6 4.7 5.4 5.3
Note: ANOVA test results suggest that there is a significant effect on ‘average travel time’ by ‘median home values’ at the p < 0.05 level for the five categories [F(4, 768) = 16.3, p = 0.000].
Current Opinion in Environmental Sustainability 2017, 25:1–7
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Commuting, energy consumption, and sustainable urban development Modarres
average travel time. Those who live in the lowest housing value category are typically located in the southern section of the Puget Sound Region. While many work in locally available employment in service and construction sectors, some do travel north for related jobs. The observed large standard deviation for their commuting time is indicative of the diversity of employment destinations for this population. This is equally true for higher priced and slightly higher density cities/suburbs east of Seattle, where higher incomes can still result in elevated commute times, which explains the increase in standard deviation for the highest housing value category. However, for all other categories, as median home value increases, average travel time declines, suggesting that lowering one’s commute time is a privilege acquired through paying for higher home values. While density is negatively correlated with average travel time (Pearson correlation of 0.223), it is important to realize who can afford this lifestyle and enjoy its benefit and who cannot. If we are to take sustainability seriously, we need to pay attention to the equity dimensions of transportation planning, moving beyond an obsession with density alone.
multiple forms of successful cities and suburbs [16]. Paying close attention to agglomeration patterns of major employers in metro regions is fundamentally important. After all, congestion is mostly produced by the uneven distribution of jobs and employees. More importantly, it is not just the number of jobs, but how salaries from those jobs match housing costs within close proximity of the employment places that matters. Having a diversity of earning potentials, matched with housing that fits those salary profiles, could produce the best possible job-housing balance for all cities, regardless of their current or aspired densities. This requires providing a range of housing options (e.g., mixed-income housing), matching the diversity of employment profiles. In other words, keeping equity at the center of land use and economic development policies could result in a more sustainable future for our cities and their residents.
References and recommended reading Papers of particular interest, published within the period of review, have been highlighted as: of special interest of outstanding interest
Conclusion In this paper, I have tried to highlight the ongoing debate around the relationship between urban transportation, energy consumption, and the urban form. While researchers are divided on the role of density, some arguing for a more nuanced discussion of density, others, starting with Newman and Kenworthy [24], have systematically highlighted its value in reducing vehicle miles traveled and energy consumption. However, one cannot ignore the question of who benefits from such an urban form under the current housing market, which puts a premium on housing value in highly dense areas, where particular sectors of the economy congregate (e.g., technology, online services, finance, entertainment, etc.). This pattern of development has created uneven socioeconomic landscapes, where those with lower incomes are subjected to longer commutes, living in lower density affordable areas outside the urban core. The fact that poverty and diversity have grown more rapidly in the suburbs, particularly the older inner suburbs of American cities, than in the central cities is a reminder of the emerging geographic divide, with its planning and sustainable development challenges.
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Following Kotval and Vojnovic [45 ], Dujardin et al. [11] and Litman [44], it is important for us to consider the issue of equity as we contemplate the future of sustainable urban development in all forms of cities and neighborhoods. While polycentricity may work well for some (e. g., [22], it may not for others. Equally, as indicated earlier, density does not always result in positive outcomes. However, a balanced approach may provide a more sustainable result, especially in North American cities. Local context matters, as does the realization that there are
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14. Futcher J, Milsm G: The role of urban form as an energy management parameter. Energy Policy 2013, 53:218-228. 15. Marique A, Dujardin S, Teller J, Reiter S: School commuting: the relationship between energy consumption and urban for. J Transp Geogr 2013, 26:1-11.
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37. Lo A: Small is green? Urban form and sustainable consumption in selected OECD metropolitan areas. Land Use Policy 2016, 54:212-220. This study utilizes various datasets to examine the relationship between urban form and sustainable consumption practices across selected OECD metropolitan areas. This research suggests that socioeconomic characteristics provide a better explanation of everyday sustainable practices than urban form, whose role aears to be modest 38. Larson W, Yezer A: The energy implications of city size and density. J Urban Econ 2015, 90:35-49. 39. Lin B, Du Z: How China’s urbanization impacts transport energy consumption in the face of income disparity. Renew Sustain Energy Rev 2015, 52:1693-1701. By focusing on 30 Chinese provinces from 1997 to 2011, this article examines the relationship between urbanization and energy consumption, while considering the role of income. 40. Yang W, Li T, Cao X: Examining the impacts of socio-economic factors, urban form and transportation development on CO2 emissions from transportation in China: A panel data analysis of China’s provinces. Habitat Int 2015, 49:212-220. 41. Lovelace R, Philips I: The ‘oil vulnerability’ of commuter patterns: a case study from Yorkshire and the Humber, UK. Geoforum 2014, 51:169-182. 42. Liu C, Shen Q: An empirical analysis of the influence of urban form on household travel and energy consumption and urban form. Comput Environ Urban Syst 2012, 35:347-357. This article explores the role of urban form in energy consumption suggesting that accessibility is more important than density and design. Furthermore, the authors suggest that urban form does not have a direct effect on vehicle miles traveled or travel energy consumption. 43. Modarres A, Dierwechter Y: Infrastructure and the shaping of American urban geography. Cities 2015, 47:81-94. 44. Litman T: Efficient vehicles versus efficient transportation: comparing transportation energy conservation strategies. Transport Policy 2005, 12:121-129. 45. Kotval Z, Vojnovic I: A socio-ecological exploration into urban form: the environmental costs of travel. Ecol Econ 2016, 128:87-98. This study focuses on Detroit and provides a detailed analysis of various dimensions of urban transportation. The authors highlight the importance of class as it relates to mode choice, distance travelled, and level of energy consumption. Their findings suggest that the highest-income grouping consumes significantly more fuel carbon monoxide than the lowest-income grouping, indicating that more equitable transportation www.sciencedirect.com
Commuting, energy consumption, and sustainable urban development Modarres
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policies, including infrastructure financing, are needed than the typical flat tax approach.
nuances that could be of special interest to transportation and land use planners
46. Mattingly K, Morrissey J: Housing and transport expenditure: socio-spatial indicators of affordability in Auckland. Cities 2014, 38:69-83. This study highlights the importance of and the need for combining housing and transportation costs to create a better understanding of affordability, especially with large and sprawling metropolitan areas. The authors apply this approach to an intra-metropolitan area of Auckland, discuss the emerging patterns, and describe some of the informative
47. Islao A, Litman T, Shahmoradi B: Testing the housing and transportation affordability index in a developing world context: A sustainability comparison of central and suburban districts in Qom, Iran. Transport Policy 2014, 33:33-39.
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48. Boussauw K, Witlox F: Introducing a commute-energy performance index in Flanders. Transp Res Part A 2009, 43:580-591.
Current Opinion in Environmental Sustainability 2017, 25:1–7
ScienceDirect Commuting, energy consumption, and the challenge of sustainable urban development Ali Modarres This paper will provide an overview of the current state of knowledge regarding commute-related energy consumption patterns. Drawing from urban transportation and built environment literature, I will suggest the degree to which the job-housing imbalance, the geography of housing affordability, and the transportation infrastructure investment have produced heightened levels of energy consumption and inequitable urban environments.
Address Urban Studies, University of Washington Tacoma, United States Corresponding author: Modarres, Ali ([email protected])
Current Opinion in Environmental Sustainability 2017, 25:1–7 This review comes from a themed issue on Sustainability challenges Edited by Chiho Watanabe, Steffen Loft, Pengjun Zhao and Tony Capon Received: 04 October 2016; Revised: 17 January 2017; Accepted: 20 January 2017
http://dx.doi.org/10.1016/j.cosust.2017.01.011 1877-3435/ã 2017 Elsevier B.V. All rights reserved.
Introduction The relationship between transportation and energy consumption has been investigated extensively. Over the last few decades, particularly after the 1973 oil embargo, a significant body of literature has engaged with this topic to either advocate for reduction in oil dependency and air pollution [1,2,3–6] or argue for further implementation of transportation demand management [7] and sustainable mobility policies [8] that reduce vehicle miles travelled, and by default, reduce auto and fossil fuel dependencies. Regardless of their perspectives, research on commute-related energy consumption patterns has largely concerned itself with the urban form, job-housing balance, and overall urban mobility patterns (e.g., [9–19], which are the main topics of the larger transportation planning literature. While the relationship between density and planning has been more regularly explored (e.g., [20–22], a growing literature is paying closer attention to the nuanced relationship between density, energy consumption and affordable housing (e.g., [23]. This literature www.sciencedirect.com
points to the trade-offs that occur when multiple public goods are simultaneously considered, suggesting that sustainable development may demand more rigorous attention to equity issues, particularly when central cities become successful hubs for economic and real estate development. In this paper, a summary of this research will be presented, arguing that a more comprehensive debate may be needed to fully consider some of the driving factors that extend the residential geography of our cities. This includes housing affordability in highly dense but unaffordable cities, such as San Francisco or Seattle, where a significant number of low to middle income employees must commute long distances to access relatively affordable housing markets. Within this research arena, the role of transportation infrastructure and the geography of major job centers cannot be ignored.
Energy consumption, urban form, and equity While transportation planning gradually shifted its attention from mobility to accessibility, promoting higher urban densities, transit, and non-motorized modes of commuting to work, there does not appear to be a universal agreement about whether the promoted strategies produce the expected results or affect different sectors of society equally. As early as the 1980s, scholars had connected the urban form to energy consumption (e. g., [6]. A few years later, Newman and Kenworthy [24] provided the foundation for comprehensively connecting commuting-related energy consumption patterns with the urban form and land use planning. This was followed by an international comparative study [25] which, among other things, recommended increasing the cost of auto ownership and use. This was due to the fact that “as density increases, both car ownership and use decline” (p. 712). This line of argument, backed by empirical evidence, albeit measured at different spatial scales and localities, has been strengthened by additional research (e.g., [26,27,28,18,29,30]. In response to the emerging debates, Burgalassi and Luzzati [31] illustrated that while there is a relationship between CO2 emission and density, “polycentriciy alone does not reduce emissions” (p. 144). Contrary to this finding, research by Yin et al. [32] suggests that a polycentric urban structure may be a better choice for compact development, and Zhang et al. [33] found that as a metropolitan area goes through various stages of development, including the appearance of new employment centers, commuting patterns and the experience of some suburbs positively Current Opinion in Environmental Sustainability 2017, 25:1–7
2 Sustainability challenges
improves, resulting in less energy consumption. Wang et al. [34] go further by illustrating how land use intensity and higher population densities contribute to higher local production of CO2 emissions. This study expanded the scope of research beyond transportation to highlight the dilemma of focusing entirely on one aspect of urban planning to proscribe or advocate for a specific urban form. However, by focusing just on transportation, Mindali et al. [35] challenged the notion that there is a simple relationship between urban form and energy consumption. Feng et al. [36], Aguilera and Voisin [2], Lo [37], Larson and Yezer [38], Lin and Du [39], Yang et al. [40], Brand et al. [3], Clark [23], Lovelace and Philips [41], Modarres [16], Liu and Shen [42], Brand and Preston [4], and Boussauw and Witlox [48] have also challenged the primacy of density in determining commuting patterns and energy consumption by addressing the nuances of who actually benefits from density, as well as commuters’ socioeconomic characteristics, gender, and patterns of automobile ownership. The findings of this body of work highlight the importance of equity and the uneven nature of most metropolitan regions. While normative assumptions about how and where we should live abound, our collective realities point to more limited choices in housing and job locations. Land value structures affect our urban social geography [43] and cannot be ignored when discussing transportation and equitable approaches to improving either mobility or accessibility. Litman [44] offers an alternative approach for mitigating auto-dependency and energy consumption by evaluating various market intervention techniques, for example, increasing fuel excise taxes, and applying new technologies, such as more efficient fuel consumption, against mobility management strategies. Through a comprehensive analysis, he concludes that the latter produce a more positive result without creating social inequities. Litman’s attention to the issue of equity is somewhat rare in earlier debates regarding the importance of the urban form in transportation planning, particularly as it relates to energy consumption. The sustainability framework that included an equity dimension to environmental and economic considerations elevated attention to this concept further. For example, Dujardin et al. [11] argue that the density solution should be viewed as a part of the picture, allowing us to consider issues of equity in urban, peri-urban and rural conditions. Their research suggests that “better-than-average performance” can be found in all types of settlements, suggesting that the way forward may be to redirect economic development and job creation in places with limited access to them. Through examining socioeconomic status and transportation behavior, Kotval and Vojnovic [45] point to the importance of class as it relates to mode choice, distance travelled, and level of energy consumption. Their findings suggest that “the highest-income grouping consumes 3.4 times the annual fuel . . . and emits 3.8 times the Current Opinion in Environmental Sustainability 2017, 25:1–7
carbon monoxide . . . than the lowest-income grouping” (p. 93) in urban Detroit neighborhoods (which excludes compact and dispersed suburbs).
Urban form, commuting and housing affordability An important aspect of commuting patterns in larger metropolitan areas is housing affordability [43], which appears to be highly correlated with population density [23]. In other words, as urban core density increases, housing affordability is diminished, pushing middle and lower income populations further away. As such, a portion of the workforce pays more for transportation in order to afford housing. Cities such as New York, San Francisco, and Seattle are highly dense and unaffordable at their cores, while relying on a large number of workers who cannot compete for housing close to work. While jobhousing indicators may illustrate a reasonable ratio, it is important to realize how many people, particularly office staff, public sector employers, and service industry workers who cater to the higher income population, must commute long distances to work. As such, these cities create a spatially-extensive commuter-shed, largely shaped by housing consumers’ attempts to achieve an optimal combination of housing and transportation costs. Under such scenarios, reliance on cars and transportation infrastructure becomes necessary. It is for that reason that Mattingly and Morrissey [46] ask that we combine the cost of housing and transportation to understand the geography of affordability in a metropolitan region. Islao et al. [47] used this Housing and Transportation Affordability Index in a city in Iran, showing that some suburban residents pay 57% of their income for transportation and housing, whereas the ideal figure is 45%. Given the importance of equity in sustainable urban development, it is crucial to acknowledge the impact of housing affordability when promoting even higher densities in urban cores. A metropolitan area cannot be sustainable if a significant portion of its blue and white collar workers must commute long distances to work in highly concentrated workplaces in central cities. In the remainder of this paper, I will explore the more recent data on four counties in the Pacific Northwest of the U.S., where Seattle is located, to illustrate the complexity of the transportation environment and its associated housing affordability dynamics. The counties of Snohomish, Pierce, Kitsap, and King, where Seattle is located, house nearly 3.9 million residents. Over the last two decades, Seattle and its neighboring cities of Bellevue and Renton have become magnets for technology companies, online services, and other employers in finance, real estate, and insurance sectors. This agglomeration, within a small geography, has generated a significant presence of service sector jobs, as well as competition for housing, which in turn has increased the cost of housing (see Figure 1) and generated a www.sciencedirect.com
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Figure 1
Median home value.
significant worsening of congestion in the region (i.e., particularly to and from Seattle). According to the U.S. Department of Transportation’s Federal Highway Administration (FHWA), by April 2015, congested hours in Seattle reached 6:38 hours, which was slightly higher than the previous year.1 Seattle was, in fact, among the seven major cities whose congestion indexes worsened in all three measurements calculated by FHWA. In other words, as Seattle’s central core has densified (as have portions of Bellevue, Renton, and Kirkland, all located along the eastern shores of Washington Lake), the cost of 1
Urban Congestion report, retrieved October 2, 2016 http://www.ops. fhwa.dot.gov/perf_measurement/ucr/reports/fy2015_q3.htm. www.sciencedirect.com
housing in these regions has moved out of the reach of many employees, and average travel times have increased. Comparing Figure 2 with Figure 1 suggests the ironic outcome. Where housing is at its highest value, average travel times are lower. These are places where high-paying jobs have matched the housing density and values. However, along the I-5 corridor and other areas where incomes are lower and housing more affordable, average travel times are larger. Table 1 reports average travel times by median home value. While census tracts in the lowest category (i.e., below $20 000) report an average travel time of 26.7 min, the second lowest category ($200 000–$299 999), which occurs in 303 tracts or 41% of all tracts in the four counties, has the largest reported Current Opinion in Environmental Sustainability 2017, 25:1–7
4 Sustainability challenges
Figure 2
Average travel time.
Table 1 Relationship between average travel time and median home values Home values
Average travel time (min)
No. of census tracts
Std. deviation
Less than $200,000 $200 000–$299 999 $300 000–$399 999 $400 000–$499 999 $500 000 or higher Total
26.7 29.8 29.0 27.0 26.0 28.4
113 303 173 97 87 773
6.5 4.7 4.6 4.7 5.4 5.3
Note: ANOVA test results suggest that there is a significant effect on ‘average travel time’ by ‘median home values’ at the p < 0.05 level for the five categories [F(4, 768) = 16.3, p = 0.000].
Current Opinion in Environmental Sustainability 2017, 25:1–7
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average travel time. Those who live in the lowest housing value category are typically located in the southern section of the Puget Sound Region. While many work in locally available employment in service and construction sectors, some do travel north for related jobs. The observed large standard deviation for their commuting time is indicative of the diversity of employment destinations for this population. This is equally true for higher priced and slightly higher density cities/suburbs east of Seattle, where higher incomes can still result in elevated commute times, which explains the increase in standard deviation for the highest housing value category. However, for all other categories, as median home value increases, average travel time declines, suggesting that lowering one’s commute time is a privilege acquired through paying for higher home values. While density is negatively correlated with average travel time (Pearson correlation of 0.223), it is important to realize who can afford this lifestyle and enjoy its benefit and who cannot. If we are to take sustainability seriously, we need to pay attention to the equity dimensions of transportation planning, moving beyond an obsession with density alone.
multiple forms of successful cities and suburbs [16]. Paying close attention to agglomeration patterns of major employers in metro regions is fundamentally important. After all, congestion is mostly produced by the uneven distribution of jobs and employees. More importantly, it is not just the number of jobs, but how salaries from those jobs match housing costs within close proximity of the employment places that matters. Having a diversity of earning potentials, matched with housing that fits those salary profiles, could produce the best possible job-housing balance for all cities, regardless of their current or aspired densities. This requires providing a range of housing options (e.g., mixed-income housing), matching the diversity of employment profiles. In other words, keeping equity at the center of land use and economic development policies could result in a more sustainable future for our cities and their residents.
References and recommended reading Papers of particular interest, published within the period of review, have been highlighted as: of special interest of outstanding interest
Conclusion In this paper, I have tried to highlight the ongoing debate around the relationship between urban transportation, energy consumption, and the urban form. While researchers are divided on the role of density, some arguing for a more nuanced discussion of density, others, starting with Newman and Kenworthy [24], have systematically highlighted its value in reducing vehicle miles traveled and energy consumption. However, one cannot ignore the question of who benefits from such an urban form under the current housing market, which puts a premium on housing value in highly dense areas, where particular sectors of the economy congregate (e.g., technology, online services, finance, entertainment, etc.). This pattern of development has created uneven socioeconomic landscapes, where those with lower incomes are subjected to longer commutes, living in lower density affordable areas outside the urban core. The fact that poverty and diversity have grown more rapidly in the suburbs, particularly the older inner suburbs of American cities, than in the central cities is a reminder of the emerging geographic divide, with its planning and sustainable development challenges.
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policies, including infrastructure financing, are needed than the typical flat tax approach.
nuances that could be of special interest to transportation and land use planners
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