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Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium (2007)

Chapter: New Mobility: The Next Generation of Sustainable Urban Transportation

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Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
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New Mobility: The Next Generation of Sustainable Urban Transportation

SUSAN ZIELINSKI

University of Michigan

Ann Arbor, Michigan


In a classic 1950s photograph, a scientific-looking man in a light suit is dwarfed by a mammoth mainframe computer he’s programming. It is unlikely that the idea of a “nanopod” would have entered his mind, let alone mesh net-working, GIS, or “Googling.” He wouldn’t have conceived of the connectivity that a mere half-century later has brought these elements together, transformed the world, and evolved into one of the fastest growing, most pervasive global industries.

Today, we are on the cusp of a comparable transformation for cities called New Mobility. Accelerated by the emergence of new fuel and vehicle technologies; new information technologies; flexible and differentiated transportation modes, services, and products; innovative land use and urban design; and new business models, collaborative partnerships are being initiated in a variety of ways to address the growing challenges of urban transportation and to provide a basis for a vital New Mobility industry (MTE and ICF, 2002).

CONNECTIVITY

An early and very successful example of integrated innovation in New Mobility is the Hong Kong Octopus system, which links multiple transit services, ferries, parking, service stations, access control, and retail outlets and rewards via an affordable, contactless, stored-value smart card. The entire system is de-

Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
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FIGURE 1 The New Mobility hub concept. Source: MTE, 2004.

signed and engineered to support seamless, sustainable door-to-door trips (Octopus, 2006).

A more recent innovation, referred to as New Mobility hub networks, began in Bremen, Germany, and is evolving and spreading to a number of other European cities, as well as to Toronto, Canada (Figure 1). New Mobility hubs connect a variety of sustainable modes of transportation and services through a network of physical locations or “mobile points” throughout a city or region, physically and electronically linking the elements necessary for a seamless, integrated, sustainable door-to-door urban trip (MTE, 2004). Hubs are practical for cities in the developed or developing world because they can be customized to fit local needs, resources, and aspirations. Hubs can link and support a variety of diverse elements:

Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×
  • multiple transportation operators, modes, and services

  • taxis and car-sharing of a variety of vehicle types and sizes

  • “slugging” (Slug-Lines.com, 2006)

  • free or fee-for-use bicycle sharing (Bikeshare/CBN, 2006)

  • walkable, bikable, and transit-oriented spatial design and development (Kelbaugh, 1997)

  • cafes and meeting places

  • wi-fi amenities

  • electronic fare-payment options and pricing mechanisms for all transportation modes and services

  • satellite-enhanced, real-time, urban traveler information for all modes of transportation provided at on-street kiosks and by PDA.

FACTORS DRIVING THE DEVELOPMENT OF NEW MOBILITY

The evolution of New Mobility is inspired by emerging innovations and propelled by pressing needs, not the least of which is rapid urbanization. Although a few cities are shrinking, especially in the developed world, by 2030 more than 60 percent of the world population and more than 80 percent of the North American population will live in urban regions (UN, 1996). With increasing motorization, traffic volume and congestion are already resulting in lost productivity and competitiveness, as well as health and other costs related to smog, poor air quality, traffic accidents, noise, and, more recently, climate change (WBCSD, 2001).

At the same time, sprawling, car-based, urban-development patterns can mean either isolation or chauffeur dependence for rapidly aging populations, as well as for children, youths, and the disabled (AARP, 2005; Hillman and Adams, 1995; O’Brien, 2001; WBCSD, 2001). In developing nations, aspirations toward progress and status often translate into car ownership, even as the risks and costs of securing the energy to fuel these aspirations rise (Gakenheimer, 1999; Sperling and Clausen, 2002; WBCSD, 2001).

ENGINEERING FOR NEW MOBILITY

The factors described above have created not only compelling challenges for engineering, but also opportunities for social and business innovation. New Mobility solution building is supported by new ways of thinking about sustainable urban transportation, as well as emerging tools and approaches for understanding, implementation, and commercialization. In this article, I focus on three frontiers of thinking and practice for New Mobility: complexity, accessibility, and new business models.

Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×

COMPLEXITY

Tools for Understanding

A variety of tools and approaches have been developed to support the analysis and modeling of complex urban transportation systems. At least three types of complementary systems analysis (top-down, bottom-up, and simulations) can be applied to transportation and accessibility. Top-down analyses generally start with self-generated variables or hypotheses and develop a causal-loop diagram using software that highlights patterns, dynamics, and possible intervention points. Once a basic analysis is complete, more in-depth data gathering and modeling can be done. Some of the most extensive transportation-related work of this kind has been undertaken by Professor Joseph Sussman at MIT (Dodder et al., 2002; Sussman, 2002; Sussman and Hall, 2004). Figure 2 shows a passenger-transportation subsystem for Mexico City.

Bottom-up, or agent-based, models are computer-based models that use empirical and theoretical data to represent interactions among a range of components, environments, and processes in a system, revealing their influence on the overall behavior of the system (Axelrod and Cohen, 2000; Miller and Roorda, 2006; Miller and Salvini, 2005; Zellner et al., 2003). Ethnographic research can also be applied to transportation as a bottom-up research tool. By giving subjects documentation tools (e.g., cameras) over a fixed period of time, patterns of behavior can be observed without interference by researchers.

Simulations and scenario-building software can draw from and build upon both top-down and bottom-up analyses. Simulations graphically depict and manipulate transportation and other urban dynamics to inform decision making and identify opportunities for innovation. MetroQuest (2006) is a good example of an effective urban-transportation simulation tool.

Sophisticated Solution Building

Complex transportation challenges call for sophisticated solutions. “Single-fix” approaches (e.g., alternative fuels alone, pricing mechanisms alone, or policy changes alone) cannot address the serious urban challenges and conditions noted above. Informed by complex systems analysis, systems-based solution building involves “connecting the dots,” that is, enhancing or transforming existing conditions with customized, integrated innovations in products, services, technologies, financing, social conditions, marketing, and policies and regulations (ECMT, 2006; MTE and ICF, 2002; Newman and Kenworthy, 1999). Sophisticated solution building usually involves multisector interdisciplinary collaboration.

A good example of systems-based solution building is the New Mobility hub network described above. Hub networks can catalyze engineering and busi-

Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×

FIGURE 2 Part of a larger analysis showing a passenger-transportation subsystem for Mexico City. Source: Dodder et al., 2002.

Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×

ness opportunities related not only to the design and implementation of individual product and service innovations, but also to the engineering of physical and digital connections between them.

ACCESSIBILITY

Over the past 50 years, measures of regional and economic success have become increasingly linked to (motorized) mobility and speed of travel (TTI, 2005). This association originated in the West and has been widely adopted in cities of the developing world. However, transportation is only a means to an end, or a derived demand, so measures and applications of accessibility do not focus on how fast or how far one can travel in a certain period of time. Instead, they focus on how much can be accomplished in a given time frame and budget or how well needs can be met with available resources. For example, on a typical day in Los Angeles, you may drive long distances at high speeds to fit in three meetings. In Bremen, Germany, a more accessible place, you may be able to fit in five meetings and a leisurely lunch, covering only half the distance at half the speed and for half the price (Levine and Garb, 2002; Thomson, 1977; Zielinski, 1995).

Accessibility can be achieved in at least three ways: wise land use and design, telecommunication technologies that reduce the need for travel, and seamless multimodal transportation. Among other benefits, connected accessibility options can help address the demographic, equity, and affordability needs of seniors, children, the poor, and the disabled. At the same time, integrated accessibility can help build more adaptable and resilient networks to meet the challenges of climate change and emergency situations in cities. Dynamic and flexible accessibility and communications systems can support quick responses to unforeseen urban events.

The University of Michigan’s SMART/CARSS project (2006) is currently developing an accessibility index to compare and rate accessibility in metropolitan regions as a basis for urban policy reform and innovation (see Box 1).

NEW BUSINESS MODELS

In a 2002 study by Moving the Economy, the current value and future potential of New Mobility markets were measured in billions of dollars (MTE and ICF, 2002). New Mobility innovations and opportunities go beyond the sectoral bounds of the traditional transportation industry. They encompass aspects of telecommunications; wireless technologies; geomatics; e-business and new media; tourism and retail; the movement of goods; supply chain management (Zielinski and Miller, 2004); the design of products, services, and technologies; real estate development; financial services; and more.

New Mobility innovations not only improve local competitiveness and qual-

Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×

BOX 1

University of Michigan SMART/CARSS Project

SMART (Sustainable Mobility and Accessibility Research and Transformation), an interdisciplinary initiative at the University of Michigan in Ann Arbor, is grounded in complexity theory and practice. The goal of the project is to move beyond purely technical and mobility-based approaches to urban transportation to address challenges and opportunities raised by the complex interactions of social, economic, environmental, and policy factors. A project of CARRS (Center for Advancing Research and Solutions for Society), SMART brings together experts on issues, theoretical approaches, and practical and policy applications to tackle the complexity, sophistication, impacts, and opportunities related to urban transportation and accessibility, particularly for growing urban populations worldwide. SMART works collaboratively across disciplines and sectors to:

  • catalyze systemic and fundamental transformations of urban mobility/accessibility systems that are consistent with a sustainable human future

  • harness emerging science on complex adaptive systems to meet future mobility and accessibility needs in an ecologically and socially sustainable way and identify “tipping points” to guide the evolution of such systems

  • inform and develop integrated New Mobility innovation and business models

  • provide diverse academic opportunities related to sustainable urban mobility and accessibility

  • contribute to a growing multidisciplinary, multistakeholder, global network of applied learning in sustainable mobility and accessibility.

ity of life (Litman and Laube, 2002; Newman and Kenworthy, 1999), they also provide promising export and economic development opportunities for both mature and “base-of-the-pyramid” markets (Hart, 2005; Prahalad, 2004). Because urban transportation represents an increasingly urgent challenge worldwide, and because urban mobility and accessibility solutions can, in most cases, be adapted and transferred, regions, nations, and enterprises that support New Mobility (supply-side) innovation, as well as industry clustering and the development of new business models, stand to gain significantly from transportation export markets in the coming years (MTE and ICF, 2002).

ENGINEERING AND BEYOND

New Mobility has the potential to revitalize cities and economies worldwide and can open up a wealth of engineering and business opportunities. But obstacles will have to be overcome, not all of them related to engineering. For example, increased motorization and the high social status it represents in devel-

Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×

oping countries, along with seemingly unstoppable urban sprawl in the West, are challenges that must be addressed on psychological and cultural levels, as well as infrastructural and economic levels. Progress toward a positive, integrated, and sustainable future for urban transportation will require more than moving people and goods. It will also involve the complex task of moving hearts and minds.

ACKNOWLEDGMENTS

Thomas Gladwin and Jonathan Levine, University of Michigan, and Moira Zellner, University of Illinois, Chicago (all members of SMART/CARSS), made helpful contributions to this paper. Background research was provided by Sathyanarayanan Jayagopi, a student in the master’s program, University of Michigan Institute for Global Sustainable Enterprise.

REFERENCES

AARP (Association for the Advancement of Retired People). 2005. Universal Village: Livable Communities in the 21st Century. Available online at: http://www.aarp.org/globalaging.

Axelrod, R., and R. Cohen. 2000. Harnessing Complexity: Organizational Implications of a Scientific Frontier. New York: Basic Books.

Bikeshare/CBN (Community Bicycle Network). 2006. Available online at: http://communitybicyclenetwork.org/index.php?q=bikeshare.

Dodder, R., J. Sussman, and J. McConnell. 2002. The Concept of CLIOS Analysis: Illustrated by the Mexico City Case. Working Paper Series. Cambridge, Mass.: Engineering Systems Division, MIT. Available online at: http://www.google.com/search?hl=en&q=sussman+%26+ Dodder+The+Concept+of+CLIOS+analysis&btnG=Google+Search.

ECMT (European Conference of Transport Ministers). 2006. Implementing Sustainable Urban Travel Policies: Applying the 2001 Key Messages. Council of Ministers of Transport, Dublin, May 17–18. Available online at: http://www.cemt.org/council/2006/cm200603fe.pdf.

Gakenheimer, R. 1999. Urban mobility in the developing world. Transportation Research Part A (33): 671–689.

Hart, S. 2005. Capitalism at the Crossroads: The Unlimited Business Opportunities in Solving the World’s Most Difficult Problems. Philadelphia, Pa.: Wharton School Publishing.

Hillman, M., and J. Adams. 1995. Children’s Freedom and Safety. Pp. 141–151 in Beyond the Car: Essays in Auto Culture, edited by S. Zielinski and G. Laird. Toronto: Steel Rail Publishing.

Kelbaugh, D. 1997. Common Place: Toward Neighbourhood and Regional Design. Seattle: University of Washington Press.

Levine, J., and Y. Garb. 2002. Congestion pricing’s conditional promise: promotion of accessibility or mobility. Transportation Policy 9(3): 179–188.

Litman, T., and Laube, F. 2002. Automobile Dependency and Economic Development. Available online at: http://www.vtpi.org/ecodev.pdf.

MetroQuest. 2006. Available online at: http://www.envisiontools.com.

Miller, E.J., and M.J. Roorda. 2006. Prototype Model of Household Activity Travel Scheduling. Transportation Research Record 1831, Paper 03.3272. Washington, D.C.: Transportation Research Board of the National Academies.

Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×

Miller, E.J., and P. Salvini. 2005. ILUTE: An Operational Prototype of a Comprehensive Microsimulation Model of Urban Systems. Pp. 217–234 in Networks and Spatial Economics 5. The Netherlands: Springer Science and Business Media, Inc.

MTE (Moving the Economy). 2004. Bremen and Toronto New Mobility Hub Case Studies and Day in the Life Scenario. Available online at: http://www.movingtheeconomy.ca/content/csPDF/BremenVideoSummaryAug2.pdf and http://www.movingtheeconomy.ca/content/mte_hubAbout.html and http://www.movingtheeconomy.ca/content/ditl.html.

MTE and ICF (ICF Consulting). 2002. Building a New Mobility Industry Cluster in the Toronto Region. Available online at: http://www.movingtheeconomy.ca.

Newman, P., and P. Kenworthy. 1999. Sustainability and Cities. Washington, D.C.: Island Press.

O’Brien, C. 2001. Trips to School: Children’s Experiences and Aspirations. York Centre for Applied Sustainability. Available online at: http://plasma.ycas.yorku.ca/documents/ontario_walkability_study_rep.pdf.

Octopus. 2006. Available online at: http://lnweb18.worldbank.org/External/lac/lac.nsf/Sectors/Transport/D5A576A039A802C0852568B2007988AD?OpenDocument and http://en.wikipedia.org/wiki/Octopus_card.

Prahalad, C.K. 2004. Fortune at the Bottom of the Pyramid. Philadelphia, Pa.: Wharton School Publishing.

Slug-Lines.com. 2006. Available online at: http: //www.slug-lines.com/slugging/About-slugging.asp.

SMART/CARSS. 2006. Available online at: http://www.isr.umich.edu/carss.

Sperling, D., and E. Clausen. 2002. The Developing World’s Motorization Challenge. Available online at: http://www.issues.org/19.1/sperling.htm.

Sussman, J.M. 2002. Collected Views on Complexity in Systems. Pp. 1–25 in Proceedings of the Engineering Systems Division Internal Symposium. Cambridge, Mass.: Engineering Systems Division, MIT.

Sussman, J.M., and R.P. Hall. 2004. Sustainable Transportation: A Strategy for Systems Change. Working Paper Series. Cambridge, Mass.: Engineering Systems Division, MIT.

Thomson, J.M. 1977. Great Cities and Their Traffic. London: Peregrine.

TTI (Texas Transportation Institute). 2005. Urban Mobility Report: 2005. Available online at: http://tti.tamu.edu/documents/mobility_report_2005_wappx.pdf.

UN (United Nations). 1996. Urban and Rural Areas. Department of Economic and Social Affairs, Population Division. Available online at: http://www.un.org/esa/population/pubsarchive/ura/uracht1.htm.

WBCSD (World Business Council on Sustainable Development). 2001. Mobility 2001: World Mobility at the End of the Twentieth Century and Its Sustainability. Available online at: http://www.wbcsd.org/web/projects/mobility/english_full_report.pdf.

Zellner, M., R. Riolo, W. Rand, S.E. Page, D.G. Brown, and L.E. Fernandez. 2003. Interaction Between Zoning Regulations and Residential Preferences as a Driver of Urban Form. Available online at: http://www.caup.umich.edu/acadpgm/urp/utesymposium/publication/zellner.pdf.

Zielinski, S. 1995. Access over Excess. Pp. 131–155 in Change of Plans, edited by M. Eichler. Toronto: Garamond Press.

Zielinski, S., and G. Miller. 2004. Integration Technologies for Sustainable Urban Goods Movement. Moving the Economy and Canadian Urban Institute. Available online at: http://www.tc.gc.ca/pol/en/Report/UrbanGoods/Report.htm.

BIBLIOGRAPHY

Burwell, D., and T. Litman. 2003. Issues in Sustainable Transportation. Available online at: http:// vtpi.org/sus_iss.pdf.

Jacobs, J. 1985. Cities and the Wealth of Nations: Principles of Economic Life. New York: Random House.

Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
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Kennedy, C., E.J. Miller, A. Shalaby, H. Maclean, and J. Coleman. 2005. The four pillars of sustainable urban transportation. Transport Reviews 25(4): 393–414.

Levine, J. 1998. Rethinking accessibility and jobs-housing balance. Journal of the American Planning Association 64: 133–150.

Levine, J. 2005. Zoned Out: Regulation, Markets, and Choices in Transportation and Metropolitan Land Use. Washington, D.C.: Resources for the Future Press.

Sterman, J. 2000. Business Dynamics: Systems Thinking and Modeling for a Complex World. New York: Irwin/McGraw Hill.

Sussman, J. 2000. Introduction to Transportation Studies. Boston: Artech House.

Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×
Page 107
Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×
Page 108
Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×
Page 109
Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×
Page 110
Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×
Page 111
Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×
Page 112
Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×
Page 113
Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×
Page 114
Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×
Page 115
Suggested Citation:"New Mobility: The Next Generation of Sustainable Urban Transportation." National Academy of Engineering. 2007. Frontiers of Engineering: Reports on Leading-Edge Engineering from the 2006 Symposium. Washington, DC: The National Academies Press. doi: 10.17226/11827.
×
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This volume includes 15 papers from the National Academy of Engineering's 2006 U.S. Frontiers of Engineering (USFOE) Symposium held in September 2006. USFOE meetings bring together 100 outstanding engineers (ages 30 to 45) to exchange information about leading-edge technologies in a range of engineering fields. The 2006 symposium covered four topic areas: intelligent software systems and machines, the nano/bio interface, engineering personal mobility for the 21st century, and supply chain management. A paper by dinner speaker Dr. W. Dale Compton, Lillian M. Gilbreth Distinguished Professor of Industrial Engineering, Emeritus, is also included. The papers describe leading-edge research on commercializing auditory neuroscience, future developments in bionanotechnology, sustainable urban transportation, and managing disruptions to supply chains, among other topics. Appendixes include information about contributors, the symposium program, and a list of meeting participants. This is the twelfth volume in the USFOE series.

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