Urban Engineering for Sustainability

I Urban Contexts and Sustainability

1 Introduction

We cannot solve problems by using the same kind of thinking we used when we created them.

—Albert Einstein

This quote from Einstein is one of my favorites, and it embodies many of the challenges that our society faces at the moment. Simply put, it is time to change the way we plan, design, engineer, and operate cities.

Going all the way back to the Neolithic era (about 10,000 BCE), the general fields of planning, engineering, and science have evolved tremendously, leading to the generation of knowledge, methods, and processes that have had significant impacts on the world. Over time they have allowed us to construct, operate, and monitor buildings in real time, to bring water to and from these buildings, to treat the solid waste generated in these buildings, and to travel from building to building via a large interconnected network of roads and rails.

Along with great progress, however, this development has also created quite a few problems, which should not be surprising. A solution to something almost indubitably creates some problems as well. Many engineering solutions developed during the Renaissance, for instance, allowed us to build larger cities and create bigger economies, which then offered the perfect venue for germs and disease to spread widely. As an example, in 1854 an outbreak of cholera killed 600 to 700 people in London (Johnson 2006). It was not until a man by the name of Dr. John Snow collected data about the people who had contracted the disease that the source of the outbreak, a contaminated public water well, was discovered.¹ Ways to treat water before it is distributed and to treat wastewater before it is rereleased into the environment had to be invented to keep the problem from reoccurring. As a more contemporary example, within the world of software engineering, fixing a bug in a code is known to easily create more bugs. Therefore, all these advances that have helped us progress so much have naturally brought their own problems. Following the words of Einstein, we therefore need to think differently and come up with new sciences and practices that can solve the problems that we face, which we will broadly fit within the term sustainability—knowing that the solutions we come up with may very well create new problems that will need solving in the future.

1.1 On the Path to Scenario B

One great way to look at this evolution of problems is from the point of view of Joseph Tainter (1988) in his seminal book The Collapse of Complex Societies. In figure 1.1 the x-axis represents the addition of new things in a society that tend to make it more complex, like the addition of new infrastructure. Staying with our water illustration, we first get water from the most accessible source, such as a nearby river or a lake. To collect, treat, and distribute this water, we need to build the necessary infrastructure, and the complexity of our system goes from x0 to x1. Thanks to this new system, we get some benefits that we can measure as y1 − y0. Now, say our city grows and we need to get water from a new source. This new source will not be as accessible as the first one, and the infrastructure needed will be more costly. We may therefore have to add the same amount of complexity to our city as we did the first time around—going from x1 to x2—but the benefits y2 − y1 will be smaller. If we go on planning the same way, the third time, the benefits will be even smaller. This is what we call diminishing marginal returns—that is, the returns for every addition decrease (we will use this concept again in chapter 2). The lower marginal returns may be acceptable for a while, but at some point we will need to figure out whether we want to take Scenario A or Scenario B. Scenario A is very common and has happened many times in the past; Tainter (1988) documents a number of examples, including the Roman Empire and the Mayan civilization. Scenario B is a lot tougher since we need to come up with new solutions, therefore echoing the quote from Einstein.

Figure 1.1

The marginal returns of increasing complexity.

The Industrial Revolution is a good example of Scenario B. Indeed, with the advances from the Renaissance and the eighteenth century, cities had grown and new technologies were needed to cope with this growth. For example, it was not before the end of the 1800s that drinking water could be pumped by large steam engines in large pipe networks. Similarly, the Industrial Revolution has created new challenges that must be faced. The difference, however, may be the scale of the problem, which has become global, and for the first time in the history of humanity, all societies in the world must work together to tackle these problems. Moreover, we cannot simply solve our problems by seeking new energy sources and consuming more resources. This is why it is called sustainability. As engineers, planners, and scientists, our goal is to create new solutions to make sure we follow Scenario B once again. This is a very challenging endeavor, and we need to revisit some of our current practices. Otherwise, we are bound for Scenario A.

1.2 Objective: Integrate Infrastructure Networks

Throughout this book we will go over many concepts, frameworks, methods, tools, and techniques that can help us toward our goal. We will, notably, see that defining and measuring sustainability is often not possible in practice, and in the absence of a systematic way to measure whether a design is sustainable or not, we will need to follow sustainability principles and hope for the best. By far the main message of this book is the need to view infrastructure systems as integrated networks. Indeed, as the scale of the problem is global, using more energy to fix our problem is not an option. We therefore need to improve the way infrastructure systems work, and we will see that they can certainly work much better if they are better integrated. Despite the fact that the issue is known, the state of the practice has too often been to view infrastructure as independent silos. At the time of this writing, this was why the various municipal, regional, and even national departments / ministries of transport, water, buildings, and energy rarely communicated and coordinated with one another. This practice must change, and we need to start by learning about each individual system ourselves, becoming demographers, urban planners, electrical engineers, water resources engineers, transport engineers, building engineers and sanitary engineers to determine how we can better integrate these systems.²

This point is particularly important because infrastructure systems are highly interdependent. Dupuy (1988) noted this point: Although only one network is capable of having an effect on urbanization, it is the totality, the combination of several different networks, that corresponds to the new forms of spatial development, redefining the territory and bringing about the transformation of local society (p. 295). This point was obvious for me when growing up in Saint Pierre and Miquelon. With roughly 6,000 inhabitants,³ Saint Pierre and Miquelon is a small overseas collectivity of France located thirteen kilometers south of the Canadian shores of Newfoundland.⁴ Despite being close to the North American continent, it is administratively entirely French and follows European regulations. This means that people on the island work in the metric system and use the 220-volt electrical standard. The archipelago needs to treat and distribute its own water (that is entirely gravity fed), generate its own electricity (using six diesel motors at the time of this writing), and manage its own solid waste (although a lot of it is recycled in France and in Canada). Growing up in Saint Pierre and Miquelon, I was quickly reminded of how everything is interrelated. Figure 1.2 shows a street that was opened up in summer 2017 to install a district heating system and to change a water main. The figure shows at least eight different types of infrastructure systems: buildings, transport (roads), electricity (both medium voltage and low voltage), water, wastewater, telecommunications, and the district heating system (that recuperates the heat being generated by the diesel motors that produce electricity). Most of these infrastructure systems need one another to function, and they are also amazingly collocated. So why were these infrastructure systems not planned together? Does it not seem obvious that they should have been planned together?

Figure 1.2

Infrastructure networks in Saint Pierre and Miquelon.

Moreover, most interdependencies that exist between infrastructure systems were not designed for in the first place. Instead, as individual infrastructure systems became more complex, they also became more interdependent. For example, early water distribution systems did not depend on telecommunications infrastructure, but starting in the 1960s, Supervisory Control and Data Acquisition (SCADA) systems have been installed to monitor and control water distribution systems remotely. What we need is to control for these interdependencies and design them in the ways we want infrastructure systems to be connected. In this book, we will learn many strategies to do so.

Essentially, we need to become urban engineers. Another term for infrastructure integration is infrastructure ecology. Figure 1.3 shows how the various infrastructure systems are interrelated. Instead of land use, we will focus on buildings, but otherwise, we will learn about the systems shown in the figure as well as about solid waste management. In addition to understanding how each system functions, we will also learn and sometimes quantify these flows (that capture the interdependencies just mentioned). One good example is that streets are often designed to accommodate a certain traffic flow. But as we experience each time it rains heavily, streets also need to accommodate flows of stormwater runoff.

Figure 1.3

Diagram of infrastructure ecology. Adapted from Pandit et al. (2011).

To partially address flooding concerns, the government of metropolitan Seoul in South Korea was quite creative. In 1968, the Cheonggyecheon River was covered with a double-story elevated expressway that was constantly congested and extremely polluting (figure 1.4a). After much debate, the river was restored in 2005, along with a scenic river walk (figure 1.4b), and the traffic was diverted to other areas of the city. The best part is that the river is also a stormwater channel that can be flooded during heavy rains. In this case, a transport problem became a water solution, and the interdependencies that came with the project were specifically designed for and therefore desirable. Put differently, the interdependencies are no longer constraining but enabling.

Figure 1.4

Cheonggyecheon River, Seoul, South Korea.

1.3 Why Cities?

Now that we have identified our ultimate goal—that we need to create new solutions to better integrate infrastructure systems—why are cities important? Cities are certainly not new; people have lived in cities for millennia. In fact, people lived in cities before they became farmers (i.e., before the agricultural revolution).⁵ Yet cities are critical to our argument for two main reasons. First, since 2008, more people in the world live in cities than in rural areas for the first time in the history of humanity. This may not seem important to people who have lived in cities their whole lives, but it is actually quite radical. Since we consume energy and resources, the way people are distributed in space has important impacts. If we see this consumption as demand, then this demand for energy and resources is shifting from being distributed over large areas to being highly concentrated in small areas. At the same time, where we get the supply to meet this demand does not change much; for example, water resources are not getting more concentrated. This therefore means that we need to revisit the way energy and resources are supplied to cities as the cities themselves get larger and larger. Moreover, this supply is also being stretched since more people are populating the planet, therefore requiring more land and more resources. We will use this supply and demand framework extensively in chapter 2 and learn about concepts of planetary boundaries as well.

The second reason, although not definite at the time of this writing (2018), is that city residents may actually consume less than people living in rural areas. This is especially true in cities and neighborhoods where a lot of people live in a small area (i.e., high population densities). In these cities, people tend to live in smaller houses that require less heating, cooling, and lighting. Moreover, people in these cities tend to either live closer to their workplace, to grocery stores, or to restaurants or can travel to these places using less energy (i.e., walking, cycling, public transport). We will go through all these points quite exhaustively in this book. There are also more people now living on Earth than ever before, surpassing the 7 billion mark in 2011 (for which National Geographic magazine [2011] dedicated a full and insightful issue, including a powerful video⁶). Most of these people live in cities, and this trend will continue in the foreseeable future to 10 or 12 billion people.

Our goal is therefore to create new solutions to provide people with the infrastructure services that they need, avoiding these diminishing marginal returns while knowing that the way people are consuming things has changed. This goal cannot be achieved without numbers, and we will need to become energy and carbon numerate to compare patterns and assess different planning and design strategies.

Engineers must also change their mentalities. The engineering practice has become overly conservative in the second half of the twentieth century. Sometimes because of fear of litigation (i.e., being sued), engineers often resign themselves to following standards, codes, and their traditional tool kit of equations as opposed to coming up with better and more creative solutions. The designer Don Norman (2013) captured it well in his seminal book The Design of Everyday Things when he wrote: Engineers and businesspeople are trained to solve problems. Designers are trained to discover problems. A brilliant solution to the wrong problem can be worse than no solution at all: solve the correct problem (p. 218).⁷ Engineers must first discover the fundamental problem they are trying to solve instead of providing a standard solution to an apparent problem that may not be the real issue. This is partly why we will spend an entire chapter on urban planning in order to understand how it used to be and how we got here. The most famous historian of cities is probably Lewis Mumford (1961), who wrote an amazing historical account of cities in The City in History: Its Origins, Its Transformations, and Its Prospects. One great quote from this book is a critique of baroque town planning: The city was sacrificed to the traffic in the new plan: the street, not the neighborhood or quarter, became the unit of planning (p. 391). Engineers therefore need to go back to the fundamentals of why we build cities in the first place: for people. The two basic questions therefore become: What kind of services do people require from infrastructure? And how can we best design infrastructure systems to provide them?

1.4 Civitas

Some of the concepts that we will see are quite easy to understand, while others will be a little trickier. To facilitate the process, we will systematically take the example of the city of Civitas. Civitas is a fictional city that we will use to illustrate some of the main concepts covered in each chapter. The word civitas comes from ancient Rome, and it represents the entity formed by all Roman citizens. It can be loosely translated to city-state, but for us it really encapsulates the residents of a city, who make a city what it is, as opposed to the infrastructure systems that are really there to service the residents. In Democracy in the Politics, Aristotle wrote, The city-state comes into being for the sake of living, but it exists for the sake of living well. This quote is particularly relevant since as human beings we form societies because we tend to live better together than alone. We should therefore make sure we plan, design, engineer, and operate cities for everyone as well. Jane Jacobs has a perfect quote on this particular aspect, which we will see in chapter 4.

In the 2010 census, our fictional city of Civitas was home to 60,000 people, Civitians, who went about their daily routines just as any resident of a city. Out of 60,000 people there were a total of 24,000 households, placing the average number of people per household at 2.5. The workforce of Civitas was composed of 40,000 people, who were all employed. Figure 1.5 shows a sketch of Civitas with its main river, Vita, which translates as life from Latin.⁸

Figure 1.5

Civitas divided into five zones.

Civitas is divided into five zones, akin to census tracts or traffic analysis zones. These zones will be our statistical units, and we will use them quite heavily throughout the chapters, as is done in practice. In particular, we will see that this is especially relevant in chapter 7 because we will calculate travel demand and transport emissions.

As is fairly common around the world, we will assume that zone 1 is the Central Business District (CBD), where most of the jobs are. Therefore, many people commute from zones 2 to 5 to zone 1 every day to go to work. This does not mean that zones 2–5 are suburbs. Instead, they contain a good mix of houses, schools, offices, restaurants, and any other types of buildings necessary for a livable community. We will see why having a mixture of building uses is important in chapter 4.

1.5 Book Outline

The book is divided into three main parts. In part I, Urban Contexts and Sustainability, we will define sustainability in urban engineering (chapter 2), and we will learn how to forecast population (chapter 3). After all, people represent our main consumers of energy, goods, and resources, and forecasting future population is paramount. We will use Civitas as an example of a typical city. We will then learn about urban planning (chapter 4), going all the way back to the Neolithic era. Importantly, in chapter 4 we will learn about our limits as people and how we perceive cities as opposed to how they actually are.

In part II, Urban Engineering and Infrastructure Systems, we will look at each individual urban infrastructure system one by one: electricity (chapter 5), water (chapter 6), transport (chapter 7), buildings (chapter 8), and solid waste (chapter 9), becoming almost experts in each. We will describe the practice at the time of this writing, study techniques to estimate energy use, and go over ways to apply the sustainability principles defined in chapter 2. This is where we will become energy and carbon numerate and where we will be able to understand electricity use in megawatt-hours [MWh], water consumption in liters per day [L/day], transport emission in grams of carbon dioxide equivalent per kilometer [g CO2e/km], building energy use in watts per square meter [W/m²], and solid waste in tons [t]. Here again, Civitas will constantly be used to illustrate the concepts and methods that we cover.

In part III, Urban Metabolism and Novel Approaches, we will learn about urban metabolism (chapter 10), which integrates the various urban systems and determines the total energy and carbon footprint of cities. We will discuss to what extent infrastructure systems are interdependent and detail some of the flows shown in figures 1.2 and 1.3. In our effort to be more creative, we will then discover the Science of Cities (chapter 11), also sometimes known as Urban Science. This field emerged primarily in the 2000s, thanks to the current profusion of data and advances in Complexity Theory. Moreover, processing new data sets and data streams needed for the Science of Cities can be cumbersome, thus we will turn our attention to Machine Learning that can be incredibly useful for processing large and complex data sets. Although the application of the Science of Cities and Machine Learning to the design of infrastructure systems was uncommon at the time of this writing, they have the potential to transform urban engineering. In particular, they can help us change our way of thinking.

Finally, we will conclude by going through two important exercises. The first will determine some of the most important changes that may completely shift the current paradigm on how cities are planned, designed, engineered, and operated. Specifically, we will identify three of these changes, two of which are purely technological, while one is organizational. Then we will elaborate a simple and short four-point urban infrastructure design (UID) process that can be used for any infrastructure project, regardless of the infrastructure type. All urban engineers can use this process as a simple guideline, and as we might expect, a higher integration of infrastructure systems is part of this process.

The appendix contains important tables, diagrams, and conversion factors that can be referred to quickly. Notably, it contains a copy of the Moody diagram and the level-of-service diagram, as well as an equation list. Moreover, by U.S. state, it contains a list of the latest power grid emission factors and the per capita consumption values of electricity, natural gas, and water available at the time of this writing.

Throughout this book, we will learn, analyze, and try to develop new and more sustainable designs for the various infrastructure systems that populate our cities, focusing on five major systems: electricity, water, transport, buildings, and solid waste. For this, we will look at the people of Civitas, the Civitians, to see how they live and how their choices affect their energy and carbon footprints. By the end, everyone should be able to understand and identify the issues that need to be solved when planning and designing urban infrastructure. More importantly, everyone should be able to come up with solutions to these issues by taking an integrated and systems-thinking approach.

1.6 Measures and Units

As we learn about the various infrastructure systems, we will be using different units, which we will generally put in square brackets [], as is conventional. Some of these units are quite easy to understand, like liters of water per day [L/day], while others may be more difficult, like watts per meter kelvin [W/(m · K)]. From personal experience, I have found that many students have a hard time understanding power in watts [W] and energy in watt-hours [Wh]. After all, in physics classes, we typically learn that energy is in joules [J]. Power is a rate of energy production or consumption, expressed in joules per second [J/s], but it was given the unit [W] (i.e., 1 W = 1 J/s) after the Scottish engineer James Watt.⁹ Then, instead of multiplying back the number of seconds produced or consumed to get energy, we like to multiply it by the number of hours. We now have watt times hours [Wh] for energy instead of [J], and 1 Wh is simply 3,600 J (i.e., 1 Wh = 1 J/s × 1 h = 1 J/s × 3,600 seconds = 3,600 J). Too often, the unit [W/h] (as in watts per hour) appears, although it does not exist. Many sources still use [J], however, and it may be easier to understand. Here, we prefer to use [Wh] consistently for energy since it is more common in practice.

Table 1.1 shows a list of units we will use in this book. By far, the use of the metric system is recommended since it is much easier to use and widely adopted around the globe. Although we may see gallons here and there in chapter 6, British imperial units will not be used. Another common unit that we will not use is the Btu, which stands for British thermal unit. Because we often find data in British units, however, some helpful conversion factors are shown in table 1.2. These two tables are also available in the appendix.

Moreover, we note that similar units do not necessarily have the same timescale. In water, for instance, we tend to use the day as the unit of time. In transport, we use the number of trips per day, but we also use total kilometers traveled per year. In electricity, we tend to use either monthly or yearly values in [MWh] since our electricity consumption can vary considerably depending on the season. In solid waste, we use metric tons per day, month, or year in general. For GHG emissions, we tend to prefer yearly values as well since our energy and resource consumption varies by season.

GHG emissions tend to be expressed as a mass, whether pounds or grams. But since we prefer the metric system, we will express GHG emissions in grams of CO2 equivalent, or simply [g CO2e]. The term equivalent is needed here because there are many GHGs. The most important are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Because they do not have the same global warming potential (GWP), the Intergovernmental Panel on Climate Change (IPCC) has come up with factors to estimate the equivalent impact of the various GHGs relative to CO2 over time. The IPCC typically uses the 100-year factors 28 for CH4 and 265 for N2O. This means that CH4 and N2O have 28 and 265 times more GWP than CO2, which is obviously significant.¹⁰

Finally, we also need to discuss conversion factors. From nano (10−9) to tera (10¹²), we often prefer to add a prefix to the unit we are using as opposed to adding a power of ten. Most of us know these conversion factors already, but here is a list:

nano: 10−9

micro: 10−6

milli: 10−3

kilo: 10³

mega: 10⁶ (or simply ton for mass)

giga: 10⁹ (or simply kt for mass)

tera: 10¹² (or simply Mt for mass)

Moreover, remember than one metric ton is 1,000 kilograms [kg] and not one megagram [Mg].¹¹ This is actually quite important. Although GHG emissions are usually expressed as a mass in grams, values of GHG emissions tend to be large and are expressed in [kg], [t], or even in kilotons [kt] or megatons [Mt]. So 1 kt is the same as 1 billion grams, but we do not write gigagram. Although it may appear a little confusing at the moment, it should be natural when we get to it.

1.7 Missing Topics

Finally, one of the personal objectives for this book was that it not be too long. This means that several important topics that fit well with urban engineering were purposely omitted.

The first missing topic is life-cycle assessment (LCA). LCA is about taking into account all emissions related to the life of a product, from the extraction of the elements to make the product to the disposal of the product itself. LCA is typically used in sustainability, and in fact it is included in most books on the topic. Moreover, it requires a lot of data and a good knowledge of all the processes involved in the life of a product. Many amazing researchers spend their entire careers computing the LCA of products and adding new energy and emissions values of certain processes. Despite the relevance, we will only briefly discuss it in chapters 5 and 10. More information on LCA can easily be found on the web, and to compute LCA, the open-source open LCA platform is recommended.¹²

In terms of infrastructure, this book does not include chapters on natural gas and on telecommunications, although both are discussed a little in chapter 10. Natural gas is also discussed in chapter 8 because it is often used to heat buildings. Telecommunications will become increasingly important because it is often used to monitor the performance of the other infrastructure systems, and it has a predominant role in the emergence of Smart Cities (which we will discuss briefly throughout the book and specifically in the conclusion). Future editions of this book might therefore have a chapter dedicated to it.

Food production and consumption is also absent from this book. In particular, emissions related to food production are substantial (especially meat products), and there is a great deal of research going on to better understand the relationships between food, energy, and water. Food may take a larger role in future editions of the book, but at the same time, it is not an engineering system as we have defined them here.

In addition, one important concept that is gaining significant momentum and that is often associated with sustainability is resilience. One of the goals is, notably, to move away from fail-safe designs and instead focus on designing systems that are safe to fail (Ahern 2011), which is absolutely relevant to infrastructure design and can be done by adopting a framework of sensing, anticipating, adapting, and learning, for example (Park et al. 2013). Although we will not define or cover resilience in an independent chapter, we will refer to it at times. The omission of resilience is chiefly due to the fact that at the time of this writing (2018), the concept was still relatively new in urban planning and engineering, and the community had yet to reach a consensus about how it could best be applied. Most often, matters of resilience are handled with optimization and operations research, often missing the central point of resilience thinking—that is, by optimizing for one aspect, a design is automatically more vulnerable to other aspects that are sometimes colloquially called unknown unknowns. A full chapter on resilience will surely be included in the future, or resilience will be better integrated in each individual chapter, but for now the reader is referred to two insightful readings: the scientific article by Woods (2015) that discusses four aspects of resilience and the critical book Antifragile by Taleb (2012).

1.8 Conclusion

In this short introduction, we were able to acquire a conceptual understanding of the main problem we face. In particular, Tainter’s diminishing marginal returns concept provides a simple and illustrative framework around which we can work. Put simply, we should focus not on efficiency but instead on providing completely new solutions to be on the path to Scenario B. As we quickly covered here, and as we will see repeatedly throughout the book, integrating urban infrastructure systems offers such a solution (think of the Cheonggyecheon River in Seoul). After all, infrastructure systems are naturally interdependent. It therefore seems logical to want to control these interdependencies, and this will be part of our role as urban engineers.

In the introduction we also covered why cities are the right places to integrate infrastructure. If we must remember one reason why this is so, we should remind ourselves that the world is increasingly urban. This does not mean we should focus only on large cities—in fact, we may or may not want to focus on small cities first since it may be relatively easier to get things done at smaller scales—but it means that we should focus on urban infrastructure (as opposed to rural infrastructure or even intercity infrastructure).

We also became acquainted with Civitas, the fictional city that we will follow throughout the book. Civitas has a population of 60,000 people, and we will soon learn more about Civitas’s infrastructure and about the habits of Civitians. From sustainability, population, and transport to electricity, water, building energy, and solid waste and even to urban metabolism, by the end of the book, we will have studied Civitas from all angles of urban engineering.

Additionally, we covered some of the measures and units that will be used in this book, and we learned about the concept of GWP used by the IPCC. Moreover, although British imperial units are still widely used in the United States, we will solely use the metric system in this book.

Unfortunately, a few topics are missing from this book. Where possible, relevant resources are recommended to learn more about a topic. We must also recognize that we still have a lot to learn when it comes to urban engineering. In particular, concepts of resilience elude most of us, and this will have to change.

After this brief introduction, it is time to start diving into the main content of the book and define what we mean by sustainability.

Problem Set

1.1 Select an online calculator of your choice to estimate your own personal year carbon footprint (i.e., personal GHG emissions). Make sure to select a calculator that accounts and reports multiple sectors—for example, transport, building energy use, electricity use, water consumption,a and more, but do not include air travel in your total. Results must be reported for an entire year and in kilograms [kg] of CO2e.b

1.2 Based on the results from problem 1.1, determine three ways that you can reduce your environmental footprint and estimate the savings with the calculator used.

1.3 In your own words, describe the concept of diminishing marginal returns by Joseph Tainter as applied to urban engineering.

1.4 In a fashion similar to figure 1.3 (infrastructure ecology), illustrate and report examples of how electricity, water, transport, and building systems depend on one another.

1.5 Similar to the Cheonggyecheon River project in Seoul, describe how one piece of infrastructure in a city of your choice could be replaced by a different type of infrastructure.

1.6 Based on your own knowledge, describe why cities play an important role in the global effort to become more sustainable.

1.7 Using the web, describe what LCA is and how it can help lower the energy used to make a product.

1.8 By searching the web, report the GHG emission factors of various food types. These types may include beef, lamb, poultry, pork, seafood, milk, yogurt, eggs, cheese, fruits, vegetables, grains, and starches. Document the sources used.

1.9 Using the GHG emission factors from problem 1.8, calculate the GHG emissions of three different meals and discuss the results.

1.10 By searching the web, find four ways to dispose of waste and discuss their respective environmental impacts.

1.11 In your own words, describe the concept of resilience and why it is important to take into account for most engineering projects.

a. If your calculator does not include water consumption, use the values given in section 2.4 (The IPAT Equation and the Kaya Identity) in chapter 2.

b. These values can be compared with your emissions calculated for individual infrastructure sectors in chapters 5–9.

Notes

1. Removing the handle of the well then prevented people from collecting water, which stopped the spread of the disease.

2. To learn about the history and how all these systems operate in New York City, The Works: Anatomy of a City by Ascher and Marech (2007) is highly recommended.

3. The surface area of the entire archipelago is 242 km² (93 mi²), but most people live in Saint Pierre, which has a surface area of 25 km² (10 mi²).

4. Newfoundland is a large island located on the east coast of Canada. Saint Pierre and Miquelon is south of it.

5. Jane Jacobs (1970) discusses this quite thoroughly in her book The Economy of Cities. We will learn a lot from Jacobs in chapter 4. Although he is not an urban planner, Yuval Noah Harari (2015) also discusses this fact quite extensively in his excellent book Sapiens: A Brief History of Humankind.

6. Available at http://video.nationalgeographic.com/video/news/7-billion/ngm-7billion (accessed August 13, 2018).

7. The same book has another great quote: We have to accept human behavior the way it is, not the way we wish it should be (Norman 2013, p. 6). Designing the perfect system is often futile if we do not take into account how people will use the system, which is often what we do in engineering.

8. I like the following quote about water from Antoine de Saint-Exupéry (1939, p. 182): You are not necessary to life; you are life. He said this upon getting to drink water after being stranded in the Sahara desert for several days.

9. Anecdotally, when I mention power to my students—say, a ten-watt lightbulb—many ask me, Watts per what? We are too used to rates being per something, like kilometers per hour, liters per day. This is simply not the case for power expressed in watts.

10. We should mention that these factors do not take into account possible feedback linked with the amount of water vapor in the atmosphere (which is actually the primary GHG). To learn more about this feedback and for a full list of factors and GHGs, see Myhre et al. (2013, table 8.A.1, chap. 8); and Intergovernmental Panel on Climate Change (2013).

11. As I have seen too many times.

12. OpenLCA, http://www.openlca.org/ (accessed March 14, 2019).

References

Ahern, J. 2011. From Fail-Safe to Safe-to-Fail: Sustainability and Resilience in the New Urban World. Landscape and Urban Planning 100(4): 341–343.

Ascher, K., and W. Marech. 2007. The Works: Anatomy of a City. New York: Penguin.

Dupuy, Gabriel. 1988. Utility Networks and Territory in the Paris Region: The Case of Andresy. In Technology and the Rise of the Networked City in Europe and America, edited by Joel A. Tarr and Gabriel Dupuy, 295–306. Philadelphia: Temple University Press.

Harari, Yuval N. 2015. Sapiens: A Brief History of Humankind. New York: HarperCollins.

Intergovernmental Panel on Climate Change. 2013. Climate Change 2013: The Physical Science Basis; Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Edited by T. F. Stocker, D. Qin, G.-K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex, and P. M. Midgley. Cambridge: Cambridge University Press.

Jacobs, Jane. 1970. The Economy of Cities. New York: Vintage Books.

Johnson, Steven. 2006. The Ghost Map: The Story of London’s Most Terrifying Epidemic—and How It Changed Science, Cities, and the Modern World. New York: Riverhead Books.

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2 Sustainability

Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.

—World Commission on Environment and Development 1987

What is sustainability? Whenever I pose this question to high schoolers or freshmen, many have not even heard the term before. If you have seen or heard the term before, chances are you have some understanding of what it means, but you might be unable to define it properly. If you have actively worked on sustainability problems or read books on the topic, then you probably have a good conceptual understanding of what it is, but can you really define it in a way that everyone understands perfectly? In reality, the term has become mainstream, and if you pay close attention, you will hear it constantly in the media in one form or another. For many people it is linked to climate change, although it really is not, or at least not directly. Many people also associate sustainability with the term green or with the environment, but again, this is only partly true (as we will see in section 2.3). We also often hear about extreme weather events, like massive floods, droughts, typhoons, and hurricanes, that are linked with climate change and that we should be greener or more sustainable. What do all of these things have in common and how do they relate to sustainability?

Starting with the 1969 National Environmental Policy Act, in this chapter we will learn about one formal and well-adopted definition of sustainability. After all, sustainability is at the core of this book, and we should really all be on the same page. The definition is in fact so clear that we will even be able to get an equation out of it that will be illustrated through an example; for those who have heard the term peak oil already, the equation will perfectly explain what it is and why we should be concerned about it. Unfortunately, we will also see that using this equation is not always possible for practical applications. To remediate this problem, we will have to define and use two sustainability principles that can be systematically applied to achieve greater sustainability. Note the use of the term greater, even though in theory it really does not make sense; either something is sustainable or it is not. That being said, at times, by fixing some problems, we may be less unsustainable.¹ At other times we may simply not be able to tell whether we are being sustainable, so we just try to aim in the right direction. We will also discuss some limitations of the principles and introduce concepts of rebound effect and interdependencies. Some of the content for this section was also published in my 2019 article An Approach to Designing Sustainable Urban Infrastructure, which also includes elements of chapter 10 and the conclusion (chapter 12) (Derrible 2019) and which can be referred to for a short conceptual summary of some of the elements of the book.

Furthermore, we will learn about the triple bottom line of sustainability, also called the Three Pillars of Sustainability, that is commonly used and that consists of people, planet, and prosperity. In particular, we will learn that no project can be sustainable if it does not contribute to the Three Pillars, and we will illustrate this point through several examples.

Subsequently, we will learn about the IPAT equation and the Kaya identity that enable us to fairly easily quantify energy consumption and greenhouse gas (GHG) emissions from just about any activity. They will also provide an excellent conceptual support to understand what can be done to lower our consumption of energy and resources.

Finally, we will learn about the concept of planetary boundaries and nonlinearities that Rockström and Steffen initially defined in 2009 and that is sometimes used in sustainability. Although not directly related to urban engineering, it offers an excellent conceptual framework to understand how the impact of a linear increase in one thing does not necessarily lead to a linear increase in something else. For example, a linear increase in carbon emissions does not have a linear impact on the climate.

Overall, by the end of the chapter, we will have acquired a solid grasp of what sustainability means and why it is relevant for urban engineering, and we will be well equipped to use the lessons from this chapter throughout the book.

Naturally, we first need to start with a definition of sustainability.

2.1 Defining Sustainability

2.1.1 Formal Definition of Sustainability

The concept of sustainability is relatively well established, and the main concept was already captured in the National Environmental Policy Act of 1969. In fact, the following paragraph taken directly from the law offers a great insight into what sustainability is:

The Congress, recognizing the profound impact of man’s activity on the interrelations of all components of the natural environment, particularly the profound influences of population growth, high-density urbanization, industrial expansion, resource exploitation, and new expanding technological advances and recognizing further the critical importance of restoring and maintaining environmental quality to the overall welfare and development of man, declares that it is the continuing policy of the Federal Government, in cooperation with State and local governments, and other concerned public and private organizations, to use all practicable means and measures, including financial and technical assistance, in a manner calculated to foster and promote the general welfare, to create and maintain conditions under which man and nature can exist in productive harmony, and fulfill the social, economic, and other requirements of present and future generations of Americans. (Jackson 1969, p. 1)

Notably, from this paragraph we can read elements of people as a society along with the environment and the economy, but we will discuss those later. We can also see that our activities can have an impact on the environment, which in turn might affect ourselves in the future. Therefore, we (collectively) need to do something about it.

To take a broader perspective, we will adopt the definition given in the quote from the beginning of the chapter: Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs. This definition comes from the World Commission on Environment and Development, more commonly called the Brundtland Report, from the chairman of the commission, G. H. Brundtland.² In fact, this definition has become one of the preferred definitions of sustainability and sustainable development. It highlights the fact that we have needs in order to survive, such as food, shelter, water, and energy, and that these needs have to be met, often by collecting energy and resources from the environment. From an engineering and economic perspective, these needs can be seen as a demand for something, and meeting these needs can be seen as the supply of something, similar to what we discussed briefly in chapter 1.

The definition therefore tells us that we should be able to produce the supply to meet our demand. We can thus assimilate the supply to a production P and the demand to a consumption C. The equation that we are then looking for is:

We are missing something, however, the second part of the definition: Without compromising the ability of future generations to meet their own needs. Future generations inevitably include an element of time. We are therefore not dealing with P and C but with P(t) and C(t). Yet, this is still not enough because P − C ≥ 0 needs to apply to all times t. As a result, instead of considering production and consumption, we need to focus on the rates of production and consumption—as the great global health and statistician expert Hans Rosling wrote: Rates are often more meaningful [than amounts] (Rosling, Rönnlund, and Rosling 2018, p. 138). Therefore, as long as the rate at which we can produce something is larger than the rate at which we consume it, we are fine. Equation 1 therefore becomes:

This is it. If we can respect equation (2) indefinitely, we should be sustainable, as in we can sustain our activity in the future. The term indefinitely is important here. It means we need to take the limit when t → ∞, and this is far from obvious. Specifically, our current society is based on growth (i.e., growth in consumption to drive economic growth), which means that C(t) is supposed to increase indefinitely, which is simply impractical; in fact, C(t) has remained constant through most of human history. Equation (2) is therefore extremely simple mathematically, but it represents an important conundrum in practice.

Moreover, we see that the equation is not directly related to the environment, although the environment is often the main component of the supply, and it is therefore an important limiting factor because P(t) cannot increase indefinitely either.³ In fact, many resources that we consume—like water, for example—cannot grow. Equation (2) therefore has limits, which we will discuss a little later, but it offers a good initial conceptual framework.

To illustrate equation (2), let us consider a simple example. Say we can harvest a fixed 10 km² cornfield that can yield 835 kg of corn per year for every 1 km²; therefore P(t) = 10 × 835 = 8,350 kg per year. At the same time, we have a population of 835 people. In the first scenario, the population eats 10 kg of corn per year per person, but the population never increases, thus C1(t) = 10 × 835 = 8,350. In the second scenario, the population only eats 5 kg of corn per year per person but grows by 10 people every year, thus C2(t) = 5 × 10t + 5 × 835 = 50t + 4,175. How do we determine which scenario is more sustainable? Following equation (2), let us differentiate the two equations and then investigate when t → ∞. In the first scenario, the population requires a lot more initially, but it is fixed, in contrast with the second scenario. Looking at the derivatives, dP/dt = 0, dC1/dt = 0, dC2/dt = 50, and therefore:

Although the population consumes more initially in the first instance, it is sustainable because the consumption does not grow in contrast with the second scenario. Figure 2.1 shows this information graphically. As we can see, the lines for P and C1 are overlapping. We therefore see that although C2 is initially much lower than C1, it catches up at one point (t = 85), and the current production simply cannot meet the demand. According to our definition, as long as we can supply future generations we are being sustainable, and therefore the second instance is not sustainable.

Figure 2.1

An example of production and consumption over time.

While this example is simple, demand is rarely constant in real life, and the second instance (i.e., C2) is quite common. While it is not sustainable, it is tolerable until a solution is found to avoid becoming unsustainable. To better illustrate this last point, figure 2.2 shows a sketch of the three scenarios that we can encounter. On the left, consumption is systematically lower than production, so it is sustainable. In the middle, consumption is currently lower than production (looking at the curves, we can see that dC/dt > dP/dt), but it will soon be higher than production. The situation is therefore not sustainable, but it is tolerable in the short to medium term. Finally, on the right, consumption is already higher than production, and thus the situation is unsustainable.

Figure 2.2

Three scenarios of production and consumption.

Instances of the three scenarios exist in real life, and we will discuss more on the topic when we learn about planetary boundaries in section 2.5, but we can list some examples in urban engineering. For instance, getting access to enough water is not a problem in many cities around the world,⁴ and water consumption is therefore generally sustainable. In contrast, most cities depend on power plants that run on fossil fuels to generate their electricity, which may be tolerable (for now) but not sustainable. Finally, one of the best examples of an unsustainable urban engineering system is transport since many cities must deal with serious traffic congestion, exhibiting signs that the system is over capacity (although this does not mean we need to build more roads—more on this later in this chapter and in chapter 7).

Despite the simplicity of equation (2) and figure 2.2, determining whether something is sustainable or not is often much more complicated. First, we simply cannot quantify everything that we produce and consume with a simple equation. In our example we assumed constant consumption in scenario 1 and constant growth in scenario 2, but this does not happen in practice. Sometimes consumption increases and other times it decreases. The general field of forecasting that tries to predict whether something is likely to increase or decrease in the future, and in which fashion, is far from trivial, and we are nowhere near to solving this problem to be able to come up with equations for every single good being produced.

Second, the consumption of a good often has an impact on the consumption of other goods. This is perhaps best illustrated by looking at figure 2.3, which shows data from the U.S. Energy Information Administration (2018). Specifically, the figure shows the evolution of total energy consumption by source in the United States from 1775 to 2017. We can see that the share of energy from biomass—that is, mostly wood burning—initially increased until the 1850s and then stayed relatively constant. This does not mean that total energy consumption remained constant—it actually increased exponentially after 1850—but it means that biomass was replaced as the main source of energy. The addition of new technologies, which cannot be imagined before they happen, can therefore have significant impacts on how much of a good is supplied. As another example, many people also have much hope for the potential of nuclear energy, but we can see that its share has stayed fairly small even though it has been used since the 1970s. We can also see that renewable sources of energy make up a small portion of the energy consumed—we cannot even see geothermal at all—but this may change substantially. We will talk more on the topic of energy consumption in chapter 5.

Figure 2.3

U.S. energy consumption from 1775 to 2017, by source.

Moreover, on the other side we need to be able to predict the demand to prepare the supply, which on figure 2.3 is the total energy consumed. In the case of energy, the consumption has increased substantially because the population has increased, but our way of life has also changed, which has had tremendous impacts on how much energy we consume. If we come back to our rates, then sustainability is achieved when the forecasted rate of production is larger than or equal to the forecasted rate of consumption. Now, knowing all of this, can you try to predict how the consumption of each of these energy sources will evolve to 2050 or 2100? Can you find an equation and differentiate it? The answer is obviously no. Remember that we consume millions of goods, some of which have an impact on the consumption of one another, not even mentioning the new goods that have not been invented yet.

2.1.2 Peak Oil, and Why Fossil Fuels Are Unsustainable

Staying on this topic, petroleum, coal, and natural gas, generally called fossil fuels, are fairly problematic for two reasons. First, burning these energy sources produces a lot of GHGs, including CO2, and adding a lot of GHGs into the atmosphere actually changes our climate.⁵ Although we will not dwell on the matter long, let us quickly look at the link between sustainability and climate change. When you change the climate, you essentially change how many things currently function, which especially affects the supply of things. For instance, crops will not grow correctly, or some important animals in the food chain will not be able to survive in their environment, which will have many impacts on the global food chain. Strong evidence also suggests that the higher frequency of extreme weather events (floods, hurricanes, extreme heat/cold, ice storms, etc.) is due to climate change (Herring et al. 2015). Overall, there is a lot of uncertainty here about what the impacts of climate change will be, but they are certain to be negative (especially because of the nonlinear nature of climate change, which we will learn more about in section 2.5), and we should at least stop releasing even more GHGs into the atmosphere. More closely related to our definition of sustainability, forecasting becomes even harder, and our ability to correctly predict and supply resources will only decrease, affecting future generations.

The second reason, which is much more closely related to our definition of sustainability, is that fossil fuels come from the processing of organic matter that has taken hundreds of millions of years to produce (hence the term fossil). Reserves of fossil fuels are therefore finite, and once we run out, we cannot extract more. How do we know when we will run out? We need to look at how many new reserves we have found in the past and how much fossil fuel we have extracted. Figure 2.4 shows worldwide petroleum production and consumption trends from 1980.

Figure 2.4

World petroleum production and consumption.

Source: U.S. Energy Information Administration. There are many relevant statistics available, and the following U.S. Energy Information Administration website offers great resources: http://www.eia.gov/beta/international/ (accessed September 3, 2018).

Naturally, both curves match almost perfectly, as supply and demand curves should. We also see that both curves currently have an increasing trend; in fact, we can fit a straight line through the points, which