Book Notes: Killed by a Traffic Engineer: Shattering the Delusion that Science Underlies Our Transportation System by Wes Marshall

Killed by a Traffic Engineer: Shattering the Delusion that Science Underlies Our Transportation System by Wes Marshall

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Posted 2025-01-22

Book Notes by John December

In this book, Wes Marshall, a professional engineer (PE) and professor of Civil Engineering, looks at the practices underlying the field of traffic engineering and finds many areas of unfounded assumptions, faulty logic, poor research methods, and spurious reasoning. He describes how our present transportation system has inherent faults that harm and kill people and reduce transportation and mobility choices. To go forward, Marshall makes a plea for traffic engineers to reform their work based on a foundation of better assumptions, empirical evidence, self-correcting methodologies, sound guidelines, quality standards, and their professional judgment to reframe the purpose of transportation: to serve people.

Marshall's provocative title grabs the reader's attention and then sustains an 88-chapter exploration of the field's faults and promising future. Works by other authors confirm this re-examination of transportation. Jane Jacobs, in Dark Age Ahead (2004), described her realization that transportation planning used psychological gaslighting to devalue public comments and called out traffic engineers who refused to look at the behavior of traffic but instead held beliefs about traffic flow that had no basis in reality (Jacobs, pp. 73-76). Donald Shoup's groundbreaking book The High Cost of Free Parking (2005) set the pattern for re-examining the root assumptions of transportation and land use for parking. Charles Marohn, also a PE, in his book Confessions of a Recovering Engineer: Transportation for a Strong Town (2021), boldly called for reforming the engineering profession. Susan Handy, in Shifting Gears: Toward a New Way of Thinking about Transportation (2023), synthesized multiple threads of research, history, and practices to show the shifts happening in assumptions about core ideas about transportation engineering.

Marshall's unique contribution is his steadfast deconstruction of multiple shaky points of traffic engineering. Marshall's aim is not to condemn engineers but to improve the field of study and practice by first changing a fundamental assumption: "The problem is that we have worked under the assumption that what traffic engineers do borders on irreproachable. That assumption limits our ability to get better..." (p. 109).

It is this spirit of reform that motivates Marshall to invite non-engineers and people who are not transportation professionals to examine his case and work together for a solution: "You don't need to be a traffic engineer or transportation planner--or any kind of expert--to read this book or join the cause. That is one of the great things about the transportation discipline" (p. 6). Marshall further invites others to join the reform discussion: "....So even if you aren't a traffic engineer, this call to action means you too. Show us our blind spots. Call us out on our engineer speak. Make sure we see the bigger picture" (p. 372).

With this invitation, I read this book eagerly and can confirm the author's prediction: "When you finish reading this book, you're going to look at your city and streets much differently. Things that never bothered you before are going to drive you crazy" (p. 6). Marshall reveals crucial aspects of traffic engineering that affect all of our lives.

I have written a much longer Book Notes file than usual because I found Marshall's book to be like a puzzle piece that I had been missing--it connects to many aspects of urbanism, transportation, public transit, land use, traffic safety, parking, and conflicts in urban planning that I have been wondering about for decades. I took seriously the author's invitation to show "the bigger picture."

I now have a better understanding of Marshall's main points:

Book Notes Outline

Our present transportation system should not be considered safe and effective.
Traffic engineers base their work on some arbitrary assumptions.
Traffic engineers create faulty infrastructure because of inadequate practices.
Traffic engineering can be improved by "re-engineering the engineers."
I see a bigger picture encompassing this book's coverage.

I. Our present transportation system should not be considered safe and effective.

Our present transportation system has serious negative safety, health, environmental, economic, and livability problems.

The death rate on our roads is unacceptable, yet it is accepted.
Marshall observes that "our road safety problem seems undeniable. More than 1.35 million people die on the roads every year. An average day ends with 3,700 dead and tens of thousands more injured" (p. 362). (See: CDC, "Global Road Safety" and The World Health Organization's estimated road traffic death rate per 100,000 population). The international comparisons of fatality rates per 100,000 population in OECD (Organisation for Economic Co-operation and Development) countries show the USA as second in the world for fatality rate, behind only Columbia (pp. 7-12). Marshall observes that road deaths do not just affect drivers or even passengers--the tragedy is that "We now kill well over 7,000 pedestrians each year in the United States." (p. 18). For young people aged 15 to 24 in the United States, the leading cause of unintentional death is motor vehicle crashes. This record of death and injury represents a stark rebuke of traffic engineering. Marshall admits why this is the case: "let me put it to you straight," for traffic engineering, "safety first is a lie. Safety has never been the top priority" (p. 21).
Traffic engineering remains in a primitive stage of study and practice.
Marshall makes an extended analogy by comparing traffic engineering to the field of medicine. He observes that from the time of Hippocrates (c. 460-370 BC), "it's been a long and painful journey for modern medicine... it wouldn't be hard to make a case that doctors killed more people than they saved" in the first 1,000 years of the discipline (p. 2).
Many people may forget the primitive state of medical practice that continued into the 20th century. Marshall points out that doctors treated patients in the early 1900s with heroin and in the 1940s with radium (p. 3). Doctors were OK with smoking cigarettes well past 1964, and some practitioners used lobotomies for routine needs until 1967. Some doctors "scoffed at the benefits of exercise" until the mid-1970s, and "Even now, many doctors won't advise walking or biking for transportation as a health intervention... because they assume that the road safety and air pollution risks outweigh the physical activity benefits" (p. 3).
As for the field of traffic engineering, Marshall observes that "Civil engineers have also been around for about 5,000 years. Like doctors, they've learned a lot in this time" (p. 4). However, Marshall admits that for traffic engineers, "we spent our first 100 years killing more people than we saved. It's about time we flip the script and start contributing to better safety" (p. 372).
Ignorance kills, and a refusal to revise assumptions and methodologies in traffic engineering continues to kill and harm people needlessly. Marshall's central thesis is that we can reform the field of traffic engineering using empirical data and science. Marshall shows that this reform requires traffic engineers to profoundly change "how they think" (p. 6).
Our present transportation system, focusing primarily on automobile movement, has warped the landscape and changed human habitation and mobility patterns, harming people and the environment.
The traffic engineering flaws and assumptions that Marshall describes have contributed to changes in the landscape and geographies of human settlements. Marshall notes the functional classification system of streets and roads that rearranged the structure and layout of cities and towns and created suburbs that were "permanently oriented to automobiles" (p. 212). Traffic engineering enabled cars but then also simultaneously disabled or degraded other modes of transportation: "The best way to sell cars is to make it unsafe, inconvenient, unpleasant, and difficult to do anything but use a car in our cities" (p. 215), including oversupply parking (p. 218). Car dependency feeds on itself--leading to more car dependency and creating circular arguments to devalue public transit, active transit, and alternatives to car-oriented development and sprawl.
Marshall recognizes criticism of 20th traffic engineering results. He quotes Traffic Quarterly of 1959 for its warning: "The family car is destroying the American city as a desirable place in which to live and work and play. The struggle is an entirely unequal one... More than $6 billion of interstate money will have been spent for highways in urban areas. All this to make cities more comfortable for the family car to pass in and out of (or through)" (p. 218). Marshall makes clear that he is not engaged in a "war against cars," as he states, "This book isn't meant to imagine a world without them. I'm mostly looking for a world where a car isn't your only viable option" (p. 7).
The larger picture around Marshall's work is that the unsupported traffic engineering assumptions and practices have been the underlying power behind the automobile orientation of the world for over a century. Megan Kimble documents the collaboration among highway builders and traffic engineers to expand highways in her book City Limits: Infrastructure, Inequality, and the Future of America's Highways (2024) and describes the ideological basis of highway expansion: "If widening highways doesn't fix traffic, why were we spending billions of dollars to widen highways? ...the answer is ideological. For nearly a century, we have been sold the idea that automobiles made us freer and more prosperous" (Kimble, p. 274). The ideology of automobile orientation, bolstered by faulty traffic engineering, grew in the 20th century using rhetoric, routine, and regulation to give rise to motordom (Norton 2008) and automobile technofuturism (Norton 2021).
Today's legacy is that cars dominate transportation and inflict harm in multiple ways, as Miner et al. (2024) examined in "Car harm: A global review of automobility's harm to people and the environment." Moreover, as researchers Walker, Tapp, and Davis (2022) describe in their article, " Motonormativity: How Social Norms Hide a Major Public Health Hazard," automobile bias remains an unexamined force that introduces environmental and health hazards. Orientation towards cars as the only or preferred means of transport can obscure alternatives and make car dependency a policy goal that has warped cities (Kay, 1997; Kenworthy, 2017; Newman & Kenworthy, 2021), endangering a healthy mix of transportation options. The result has been a transportation system that has reinforced increasing car dependency, caused harm and deaths, and reduced the diversity of transportation options.

II. Traffic engineers base their work on some arbitrary assumptions.

Assumptions, like axioms in mathematics, set the stage for a system of knowledge so powerfully that flawed assumptions can lead to wasted time and resources in faulty and ineffective practices. As Marshall describes, traffic engineering and related transportation and planning fields can form assumptions based on faulty research, poor reasoning, or unsupported estimates. What is worse, traffic engineers doggedly and arrogantly defend these methods based on loyalty or the belief that their long-held use is proof of their validity and that the non-engineers who criticize the results are ignorant.

In looking at Marshall's book, I think the top flawed assumptions of traffic engineering are:

Traffic engineering borrowed concepts from structural engineering without evidence of applicability and assumed away or ignored observable human responses to built transportation infrastructure.
Marshall explains how traffic engineering took on the factor of safety assumption as "one of the underlying problems in traffic engineering" (p. 51):
"Fundamental to structural engineering is the factor of safety concept. In other words, we try to design things like bridges and buildings to handle something on the order of three times the design load..." So in traffic engineering, "we calculate that two lanes will accommodate the expected traffic but assume that four lanes would be better because they give us a bigger factor of safety. We think we need 20 parking spots but have room and money for 30, so why not? It'll give us a nice factor of safety" (p. 51).

The fundamental reason why the factor of safety assumption does not work is that it ignores the human response to the built infrastructure. In structural engineering, forces and materials react as predicted, but in traffic engineering, sentient human beings react intelligently and also emotionally to the infrastructure presented to them. Marshall explains: "At first, it makes perfect sense to build a factor of safety into our transportation system to keep people safe. But if that factor of safety tempts people to drive faster and more dangeriously, a higher design speed isn't the factor of safety we signed up for" (p. 53).
The factor of safety assumption sounds good, and engineers may earnestly have felt that it guaranteed safety, but in practice, it often does the opposite. Traffic infrastructure has been vastly over-built based on this assumption, with negative safety and usability consequences that affect (and kill) people, drag down the livability of communities, and require high costs to maintain every single hour of every day. Marshall appeals to overturn this assumption: "... transportation engineers go about our jobs with a structural engineering mentality" (p. 51).
Traffic engineers assume that adhering to standards will assure safety and shield them from liability, responsibility, or guilt for their work.
Traffic engineers assume that they work for road safety as the #1 priority while evidence proves otherwise. Marshall states:
"The tragic disconnect is that traffic engineers believe they've been trained in road safety because they believe the manuals are steeped in a century of road safety knowledge. They aren't. The reality is that much of what we learn as traffic engineers has nothing to do with actual road safety outcomes whatsoever. That is why traffic engineers don't take too kindly to suggestions about road safety. That's why traffic engineers believe in things that diverge from common sense when it comes to road safety. That's why others look at traffic engineering like a religious cult." (p. 74).

The excuse that "we were only following standards" is no longer an adequate defense for faulty traffic engineering.
1. Ignoring evidence, common sense, and disregarding compassion for human life with an appeal to "standards" may no longer shield any professional who willfully pushes a poor design. Marshall's work in this book and Charles Marohn's statements in his 2021 book Confessions of a Recovering Engineer reveal an awareness of faulty traffic engineering standards and practices. No traffic engineer can claim ignorance of this issue anymore.
  At one time, courts were only concerned if engineers followed standards (p. 254). On top of that, arbitrary laws further shielded liability for any crash with deadly results. For example, New York State's "rule of two" law held that two significant violations of traffic laws had to occur for a charge against the driver. This "rule of two" created an easy deathtrap for pedestrians so predictable that it might form the basis for "the perfect murder" (as described by Stephen Dubner, p. 255) because killing a person on the street could easily lead to the driver going "scot-free" (p. 255).
  Now, courts of law are holding engineers and the cities they work for responsible for their transportation infrastructure decisions. In 2004, a driver on Gerristen Avenue in Brooklyn seriously injured a child bicyclist. A court held the City of New York liable "because the city failed to take adequate measures to prevent the speeding motorist from breaking the law." The judgment found the city was liable for 40%, the driver 50%, and the bicyclist 10%. The basic finding was that, although Gerritsen Avenue met engineering guidelines, it was known to be an unsafe street because many people had complained about the speeding drivers and bad safety. Marshall observes, "In other words, the city lost this case because it blindly followed the guidelines and ignored the empirical evidence" (p. 259).
2. Traffic laws built on faulty engineering design do not ensure safety.
  As Marshall observes, "...emphasizing the rules of the road benefits traffic engineers but harms everyone else" (p. 273). Marshall cites a Transportation Quarterly paper stating that "the commonly held notion that lawful behavior equals safe behavior is not borne out by statistics" (p. 271). As Marshall states, the assumption that traffic law is safe is absurd because "...people respond to the transportation system we put in front of them....." (p. 272).
  Drivers also cannot make the excuse that "I was only following traffic law" to absolve blame. Marshall quotes a Transportation Quarterly paper by Pucher and Dijkstra (2000), stating, "in almost every case, the police and the courts find that motorists should anticipate unsafe and illegal walking and cycling. Having the right of way by law does not excuse motorists from hitting pedestrians and cyclists" (p. 274).
  Human response to traffic infrastructure based on faulty design criteria cannot be ignored: "... dig into many of the design criteria that we use today--like the side friction factor or perception-reaction time--and you'll see that we were flying by the seat of our pants" (p. 287). In contrast, Marshall maintains this fundamental idea: "Traffic engineering impacts human behavior, which in turn impacts road safety" (p. 53).
3. The rhetoric of crash descriptions deflects blame and implies a false belief in standards, contradicting what we observe in the real world.
  A convenient way to disperse responsibility for a crash is to, "in some cases, we blame nobody and chalk it up as a so-called unfortunate accident" (p. 258). Next, we can "blame the driver for speeding or the kid for not bicycling where he should or for wearing dark clothes" (p. 258). A passive voice in crash descriptions "habitually depersonalizes the driver..... they'll say that a pedestrian was hit by a car" (p. 267). This depersonalization leads to absurd headlines such as "Woman Dies from Injuries after Car Jumps Curb," in the NY Post (p. 268).
  Marshall advocates reworking the assumption that laws based on faulty design are, by definition, safe: "If we want to save lives, traffic engineers might want to assume that all human error is engineering error. This isn't for liability purposes. I'm strictly talking about the need for traffic engineers to reconsider their work" (p. 113).
Some traffic engineers and the public hold flawed assumptions about the fundamental definition of transportation, its purpose, and its goals.
While teaching, Marshall engages his students with a classroom exercise. He simply asks the class, "what's the point of transportation?" (p. 358). Of course, many students state the seemingly "obvious" answer: "to get from A to B." However, Marshall presses the students with questions about mobility and how it relates to gaining access to resources--and how this relates to the whole purpose of transportation, and then "I start seeing the light bulbs go off. At that point, the discussion shifts from questioning how we can improve mobility to questioning how we can improve access. The answers shift from things that we hope could maybe, possibly fix traffic congestion to issues like active transportation, transit, land use, and community design" (p. 358). Marshall's teaching point is that "... if we stop focusing on getting from A to B as quickly as possible and think more about ways to bring A and B closer together, we might get there faster as well" (p. 357). (See also Moreno 2024).
The commonly-held assumption that "transportation is about moving people and goods from point A to point B" implies that traffic congestion is the problem in cities and other areas (p. 106). However, Marshall seeks a subtler, finer understanding: "at its core, transport is about connecting people, goods, services, and activities. We want to make it easy and safe for people to access schools, jobs, shops, restaurants, hospitals, health care, concerts, social gatherings, parks, nature trails, and so on." Solutions then can involve improved transit, land use, and the location of resources around and at points A and B. We can ask, "Do you need to be in a car to get there, or did we provide a range of safe and reliable options?" (p. 106).
Traffic engineering assumes that a set of quantities—for example, cost, road capacity (including projected capacity 20-30 years in the future), vehicle speed, and level of service—are paramount in transportation infrastructure design without regard to their results, effectiveness, impacts, validity, appropriateness, or the needs of individuals or communities.
Traffic engineers are deeply set on their focus on specific quantities regardless of results or public response. At the end of his 2021 book Confessions of a Recovering Engineer: Transportation for a Strong Town, Charles Marohn gives a stunning admission of the faults of his past engineering work (he is a professional engineer):
"I allied with those who wanted wider streets, faster speeds, and greater volume because we had shared interests that I believed were enlightened... I joined with others in my profession to ridicule and marginalize those who disagreed with the standard industry approach. I was not open to criticism, reassuring myself that any truly valid critique would come from within the profession" (Marohn, pp. 231-232).

Another example involves highway expansion. With the goal of cost reduction, engineers planning highway expansion worked to find the least-cost paths through cities to destroy neighborhoods for interstate highways (Kimble 2024). They had no regard for the communities of people in these paths or the discriminatory and arbitrary destruction and long-term damage they caused (Davis 2023).
The darker history is that planners inflicted the destruction on minority communities with zeal: "we've seen that traffic engineers systematically, intentionally, and repeatedly place big arterials and freeways directly through lower-income and minority neighborhoods" (p. 226). Madison Grant created the Bronx River Parkway in NYC in 1908, and "Grant's fellow parkway commissioners... took pride in their parkways cutting through low-income, immigrant neighborhoods" (p. 228).
The quantities measuring road safety show deceptive assumptions. The conventional metrics hold that road safety = number of fatal crashes/number of miles driven. Therefore, increasing the number of miles driven (denominator) increases safety: more cars driving more miles = more safety (p. 85). However, Marshall reveals the ridiculousness of this assumption and suggests, "what if we treated road safety like any other public health issue and calculated our fatality rate using population as the exposure metric?" (p. 85). The fundamental assumption of measuring safety in terms of the number of miles driven is faulty because it rewards the expansion of massive movement of cars to improve road safety.
Other metrics used in traffic engineering are also based on traditions and "old beliefs," such as wider driving lanes are safer. The priority on capacity demands wider lanes (p. 182). The truth is that researchers found "narrower lanes meant fewer injuries and fatalities" (p. 181), and this was due mainly to the human reaction to wider widths (to drive faster) (p. 181). The assumption that driver comfort equates to safety has to be overturned (p. 284).
The assumption of automobility--the assumed belief that the automobile is the rightful prime directive of transportation--has been melded into our society, and the underpinning for this belief rests in part on the faults of traffic engineering that Marshall uncovers.
Marshall reveals the faulty traffic engineering assumptions and practices that place automobile infrastructure and movement as a priority in transportation and land use decisions. This contributes to the underpinnings of automobile bias. Peter Norton described the century-long effort, as traffic engineering developed in the 20th century, to place the automobile at the apex of transportation (Norton 2008) and and the nearly century-long and continuing campaign of technofuturism to keep it there (Norton 2021).
The key insight Wes Marshall adds is that faulty engineering underpins and warps the decision-making process for the design of streets, roads, highways, intersections, and automobile infrastructure for cities. More than two decades before Wes Marshall, Alex Marshall, in his book How Cities Work: Suburbs, Sprawl, and the Roads Not Taken (2001), showed how cities work by the confluence of people and goods moved about and concentrated by transit and how 20th-century cities have focused on just one transit mode, automobiles, to the exclusion of others. From putting together the ideas of these two Marshalls from 23 years apart, we can see that the fundamental layout of cities has been warped by faulty traffic engineering, putting cars first. This insight corresponds to other accounts of cities and their lost potential. In Dead End: Suburban Sprawl and the Rebirth of American Urbanism (2014), Benjamin Ross makes the case that the inherent strengths of cities can be unleashed if land use policies are reformed. However, the automobile bias, underpinned by faulty engineering reasoning, must be revised to do this. Wes Marshall's book identifies faulty traffic engineering assumptions as contributing to these historic changes in the landscape.

III. Traffic engineers create faulty infrastructure because of inadequate practices.

Some methods, research, and guidelines for traffic engineering are faulty because they use unfounded assumptions, lack a mechanism to self-correct, remain stuck in silos of practice, relentlessly follow a tunnel vision focused on automobiles, lack attention to the larger context of individual and community life, fail to recognize the predictable human response to built transportation infrastructure and ignore the fundamental purposes of transportation, land use, human habitation, mobility, and access.

Underlying methods of traffic engineering can produce dangerous and inadequate results.
Traditional traffic engineering uses assumptions, standards, design criteria, and methods to create transportation infrastructure. With faulty assumptions and poor standards, Marshall states:
"The reality is that when we combine the conventional traffic engineering approach to our three main street design criteria--design capacity, design speed, and the design vehicle--traffic engineers end up building every city's high-injury network.... The fundamental idea behind a high-injury network is to identify the streets where most of our serious injuries and fatalities take place" (p. 178).

Thus, traffic engineers, working earnestly according to their training, have unfortunately participated in "the creation of the deadliest streets in most every city" (p. 179). Marshall has looked at dozens of high-injury network analyses done for cities, and "Every time, the map ends up highlighting the exact big roads where state departments of transportation have emphasized the conventional, capacity-based traffic engineering design approaches described here" (p. 179).
Based on these dangerous results, Marshall appeals for traffic engineers to reassess (pp. 366-369):
- Standards, "which have been built on a rickety foundation of pseudoscientific theories."
- Design guidelines and processes that "encourage more speed, more capacity, and more driving."
- Safety metrics that "reward more driving, to the detriment of safer humans."
- Oversimplified crash data that "reassures us that the safety problems are not the fault of traffic engineers."
- Misplaced blame where "traffic engineers blame everyone but ourselves and expect enforcement, education, or technology to save the day."
- A fear of liability that serves as a "built-in excuse not to do better."
- Inadequate training of the next generation where "traffic engineers fail to teach the next generation of traffic engineers to be better."
Marshall admits better practices might mean profound change: building "safer streets instead of less congested streets" (p. 369), being "proactive about collecting data on problems and work toward fixing them" (p. 266), dropping the reliance on standards as the final word to "shut down discussion" (pp. 281-282), and reassessing "the fundamentals of... everything we do" (p. 367).
Traffic engineers sometimes work confidently with methods and assumptions they think are "obvious" but lead to faulty designs.
Marshall states, "One thing I love about transportation is how counterintuitive things can be" (p. 187). Traffic engineers make assumptions about what will lead to better safety, but unfortunately, they do not always subject their design to empirical observation. Marshall's examples in this area include:
1. Belief: Traffic will flow more quickly or more safely with additional or wider lanes.
  Reality: "time and time again, the seemingly simple solution fails. Instead of the same people doing the same thing at the same time of day, people adapt to what we've put in front of them" and induced demand fills in the additional lanes (p. 187). The general principle is that when drivers feel safer, they drive faster (p. 191). (See also: Todd Litman, "Generated Traffic and Induced Travel" and Transportation for America 2020, "The Congestion Con: How more lanes and more money equals more congestion".)
2. Belief: One-way streets are safer.
  Reality: "when we design one-way streets for high capacity and high speeds, we end up with highway-like streets that create barriers instead of bonds. Streets represent the building blocks of our cities, and any city street that 'stands as a fundamental hazard to persons on foot' doesn't seem like building block we want to start with." (p. 186). Traffic engineers "assumed that some other thing--like fewer conflict points in this case--would automatically improve safety. Unfortunately, transportation is rarely that simple" (p. 186).
3. Belief: A clear zone that removes trees and fixed objects proximate to traffic flow increases safety.
  Reality: "The clear zone mentality is one of the biggest missed opportunities in urban areas. We could be proactive and use trees or other fixed objects help slow speeds and serve as protection between cars and more vulnerable road users." (p. 195).
4. Belief: Hierarchical street networks, based on a tree-like system of roads branching off from arterials to collector roads to local roads (the patterns of the suburbs), are logically the best way to design streets.
  Reality: Grid street patterns have demonstrated safety and efficiency for centuries. Marshall points out that the origins of the hierarchical street networks were based not on rationality but on an emotional contempt for grid street patterns. As shown in the 1929 design for Raedburn, NJ, engineers touted the hierarchical streets under "the guise of patriotism and as a way to get away from immigrants." The Federal Housing Administration (FHA) said those hierarchical branching street networks were "good" and gridded street patterns were "bad" without evidence (p. 206). Marshall found that: "compact and connected street networks have between 27 and 44 percent fewer road fatalities than conventional sparse, tree-like street networks" (p. 204).
5. Belief: Engineers classify roads as being either urban or rural.
  Reality: The functional classification system that recognizes roads as being just urban or rural misses out on a "second dimension," which includes "physical setting, context, land use, ... (and) local conditions" (p. 209). The binary insistence on either urban or rural streets and roads may be convenient for design and construction (p. 210); however, "streets like that--backed by a faulty functional classification system--are killing us." (p. 211).
6. Belief: Traffic engineering should aim to move cars as fast and inexpensively as possible.
  Reality: Marshall points out that using this approach, "We ended up with problems because traffic engineers never bothered asking what the social, environmental, or long-term economic consequences might be" (p. 222).
In the end, Marshall states, "Design details matter, but it would take another whole book" to cover them (p. 192). He summarizes: "traffic engineering outcomes are often counterintuitive... traffic engineers have a history of overlooking the disconnect between what we think leads to better safety and what actually does" (p. 187).
Traffic engineers relentlessly focus on level of service (LOS), capacity, vehicles, and speed but fail to consider human factors and the design purpose of transportation.
Traffic engineers prioritize car movement and have devised a set of numbers and grades that reflect this imperative. By having these scalar measures, they can make arguments, seemingly scientific, to pave the way for automobile flow but fail to consider the big picture: the human reaction to transportation infrastructure and the purpose and context of transportation, particularly for the lives of people and communities in which these cars flow.
Level of Service (LOS) refers to a qualitative evaluation of the flow of traffic on a road or street in terms of a capacity-focused letter grade from A (free-flowing traffic) to F (traffic jam) (p. 291). Sometimes requirements for LOS are codified into law, and traffic impact analysis holds that "anything that adds to driver delay or slows car speeds could make LOS worse" and, therefore, must be mitigated--perhaps involving "increasing the capacity of the adjacent intersection or street" (p. 292). In other words, anything like a crosswalk for pedestrians, an increased number of cars on a streetcar, or narrower or fewer traffic lanes could reduce the LOS grade for cars and must be rejected unless a neighboring street is made wider.
For example, a Barnes Dance, an all-pedestrian, all-direction—even diagonal—signal phase for intersection crosswalks, worked well to reduce fatalities (p. 294). However, accommodating pedestrians with a Barnes Dance lowered the LOS for cars at the intersection, and so it was discontinued—an example of LOS driving a "policy decision based on" cars (p. 294).
The imperative to move cars--lots of them at high speed--underlies the general fear of traffic engineers have of congestion (p. 173). This fear results in a set of numbers chosen to lay out imaginary scenarios for the highest possible demand on a road now and in the future and then overbuilding aspects to guarantee that the LOS grades will be high for those rare cases of high demand. Marshall explains the implication:
"We are theoretically trying to accommodate traffic levels during the peak hour by estimating the design capacity, also called the design hourly volume. The design hourly volume typically equates to the 30th highest hourly volume... [which] means that if we take all the hours in a year and rank them in order by traffic level, there are only 29 hours over the course of a year with more traffic than the design value. It also means that there are 8,730 hours in a typical year with less traffic than the design value. For intersections, we take it a step further and estimate the traffic during the peak 15 minutes of a typical peak hour." (p. 173).

And then, the scenario is projected 20 years into the future, using estimated growth factors. This dizzying line of reasoning may seem scientific because it uses numbers. However, Marshall points out, "Instead of designing for the amount of vehicle traffic we deem appropriate, we think it's our job to accommodate whatever future traffic these growth factors predict" (p. 176). The result is, in traffic engineering, "we size our streets for a busy rush hour 20 years into the future while simultaneously designing it for the speeding we expect when the street is empty. This process isn't about safe streets. It never was" (p. 166). Marshall laments: "The traffic engineering mind-set toward speed has cost tens of thousands of people their lives. It still does" (p. 171).
Setting speed limits for roads also suffers from convoluted arguments to make way for fast cars. Marshall explains that engineers set speeds on streets based on the 85th percentile guidelines, the speed at which, in free-flowing conditions, 85% of vehicles are traveling under it. However, "In trying to be conservative, traffic engineers probably selected a design speed of 60 or 70 mph even though they want people driving 40 or 50 mph" (p. 162). The result is "we disregard common sense" and set a speed limit higher than the design speed (p. 163). Then, the excuse is that "... we like to leave speed up to 'personal responsibility.' But sadly, more than 35 percent of those who die in speeding-related road crashes are not the people who were speeding" (p. 170).
Another part of design factors is the design vehicle--considering the width, length, and height of vehicles that might travel on a road given its classification (p. 177). The method, as in other quantities, is to imagine the largest vehicle that might come along and "to design streets for the biggest and least maneuverable vehicle that may use it" and this leads to large turning radii, which lead to high speeds drivers take on turns (p. 177).
The bottom line is that by using numbers and the LOS grade, traffic engineers justify excessively-large transportation infrastructure that does not improve safety because the human element--for example, the tendency for drivers to go faster when they feel safe--nullifies the claim of safety. Marshall laments, "Where does that leave us? With big roads and low speed limits just begging us to go faster" (p. 163).
The root part of the problem of this engineering approach is "that too many of our engineering solutions treat people like inanimate carbon rods. For example, we've long treated traffic flow like water in a pipe [while] the more enlightened traffic engineers now realize that traffic is more like a gas. Why? Because people change their behavior based on the transportation system we put in front of them." (p. 53).
Traffic engineers relentlessly work to increase the Level of Service, speed, and capacity and disregard human agency and reaction to the built infrastructure. The resulting overbuilt automobile infrastructure works against safety and the effective use of active and public transit.
Traffic engineers use a clever technique to deflect responsibility from their engineering designs.
The promoted practice in traffic engineering is that engineering, education, and enforcement are sufficient for safe roads (pp. 35-36), and this is both a mantra for traffic engineers and a way to hide responsibility in a way similar to a three-card Monte con game. Marshall reveals how this works: "Once we've [traffic engineers] built the street, how fast people drive is out of our hands. If people drive too fast, they need more education. If that doesn't work, we need more enforcement... The truth is we need better engineering" (p. 50).
Marshall identifies the true nature of the situation: "enforcement--akin to education--is a crutch that traffic engineers use to keep the focus off of them. The bottom line? If we need to rely entirely on enforcement to police our streets, we've done a bad job of designing our streets." (p. 46). The deflection works by assigning 95% of crashes to "human error" and thus justify education and enforcement as the solution (p. 110). The root issue Marshall raises is that humans react in deadly ways to poor engineering: "What traffic engineers fail to realize is that their definition of human error is a symptom of conventional traffic engineering" (p. 115).
Traffic engineers frequently miss out on a powerful insight: what is predictable is preventable.
Marshall's theme of traffic engineers disregarding human behavior has another dimension: predictability. He observes:
"Most crashes are predictable. Most human error falls into recurrent patterns. We know exactly when certain types of human errors take place. We even know why certain types of human error take place. But when that human error coincides with a crash, it's easy to blame the human error. Traffic engineers--and engineering in general--are off the hook" (p. 114).

In the transportation system, active errors are specific things people do (for example, driving the wrong way up a one-way street) (p. 117). Latent errors are embedded in the transportation infrastructure design (such as a street intersection layout to allow permissive left turns across multiple lanes of traffic while pedestrians are in the crosswalk) (p. 117). What happens is that latent errors are hidden in the infrastructure itself--the engineers putting these errors into the infrastructure are long gone when a crash occurs. However, these latent errors lead to active errors (a driver taking a left turn crashing into pedestrians in a crosswalk (p. 114)), and "traffic engineers then treat active errors as random errors, never looking to the latent conditions that lead to their predictability--and to our underlying road safety issues" (p. 117).
Marshall points out that "... it's the latent errors in the transportation system that are the most insidious. It's our refusal to deal with the latent issues practively that keeps us spinning our wheels, never making any headway on real road safety improvements." (p. 118). (See also: Dangerous by Design).
Traffic engineers can miss out on insights gained from observation.
In teaching, Marshall gives his students a "charming streets" case study project: find a subjectively pleasing, charming, beautiful street, compare it to a nearby street with a poor safety record, and evaluate each street according to the traffic engineering manuals (p. 288).
Students find that the manuals are OK with the unsafe streets, but the "charming streets" are terribly out of compliance. The charming streets do not comply with "lane and shoulder widths, vertical and horizontal curve radii, lateral clearances and offsets at the street edge, and other geometric features," and the level of service is low (p. 290). Marshall's lesson is, "No wonder we still haven't wrapped our heads around the speed-and safety--implications of basic street dimensions... research has not been done properly" (p. 289).
The "charming streets" case study illustrates the most potent activity of science: observation. Observation includes looking at lessons from history:
- "It's the older cities--mostly built before traffic engineers existed--that tend to be safer" (p. 202).
- "The older cities seem more compact, with a connected network of streets. The newer cities appear sparse, with a disconnected network of streets branching out like a tree" (p. 202).
- Marshall found that: "compact and connected street neworks have between 27 and 44 percent fewer road fatalities than conventional sparse, tree-like street networks" (p. 204).
- People who lived in compact connected street networks also drove fewer miles and had better health outcomes (p. 205).
Traffic engineers can fail to gain insight from observing simple relationships from Physics 101:
- Speed matters: The basic equation is distance = rate * time. In calculating stopping sight distance or determining a road's design speed, traffic engineers must increase the rate (speed) to cover longer distances in a given time. It does not seem to dawn on them that by providing access to resources closer in distance, the rate (speed) can be vastly reduced to cover the smaller distance in the given time. Marshall describes how misconceptions about the value of speeding in cities show that higher speeds do not save much time and are unsafe: "we turned hundreds of years of common knowledge into a giant question mark. Worse yet, we shifted the conversation so that speed seems negligible in safety" (pp. 168-169). Considered in isolation, this assumption to increase automobile speeds at all costs, when pursued in the majority of transportation infrastructure designs, creates large distances for people to travel and ignores or damages the operations of other modes of travel, such as active or public transportation.
- Force matters: The basic equation is force = mass * acceleration. In the event of a crash, acceleration is negative, and the sudden decrease in velocity for a high-mass, high-speed vehicle results in tremendous force--leading to severe injury or death for pedestrians in the way. When traffic engineers ignore or downplay this, their designs contain latent faults that hide deadly safety problems posed by speeding automobiles to pedestrians.

IV. Traffic engineering can be improved by "re-engineering the engineers."

Wes Marshall, a PE himself, empathizes with engineers who seek to do their best based on what they have been taught. Marshall also repeatedly observes that engineering judgment is built into the present system, so traffic engineers can even now make better decisions. Leveraging the desire to do better and the ability to do better, Marshall calls for improved education for traffic engineers.

Traffic engineers must gain focused technical expertise but also an appreciation for how their work affects people.
Marshall provides a way forward by suggesting what traffic engineers could do immediately: gain empathy. Marshall suggests that engineers experience the streets they built by walking them and trying transit and empathize with pedestrians, their experiences, and their choices (p. 324). Similar with driving: drive along roads and through intersections not as an engineer but as a person new to the situation and note what the transportation infrastructure shows to you and tells you to do. Have empathy for users (p. 324).
Next, traffic engineers need to appreciate the bigger picture of transportation purposes. All life does not revolve around automobiles. Marshall observes that "cities with good transit have good road safety" (p. 349). Transit saves lives-- research shows that a 1% rise in transit mode share corresponds to a 3% drop in traffic deaths per population--"Fewer people tend to die on our streets when more people use transit" (p. 349). Furthermore, as Alex Marshall showed, transportation shapes the city (2001). However, a blind spot of some traffic engineers seems to be public transit. Marshall observes, "Transit is about 20 times safer--in terms of fatalities and severe injuries--than driving. Yet, for whatever reason, we never sell transit as a safety intervention" (p. 352). Marshall states, "If our streets are the bones of our cities, transit is the connective tissue" (p. 353).
Marshall identifies specific related work of traffic engineers that affects the lives of people daily, such as parking, land use, and transit-oriented development. He advocates that parking is a key category to work on in addition to transit (p. 349; see Shoup 2018). The simple observation that empty parking lots do not aid transit motivates transit-oriented development, augmented by direct walkways from housing to transit platforms (p. 350). Marshall advises making transit shelters pleasant and safe, make it easy to know how to use and get real-time information, and have good walking and biking connections (p. 351). Further, avoid big parking garages and park-and-ride projects (p. 351; see also Mepham 2024).
The larger picture of traffic engineering includes an understanding of how traffic engineering impacts how people live, work, and travel using many different transit modes and routes. Marshall advocates that traffic engineers should focus on improving travel for kids, active transportation (walking and bicycling), public transit, and a reduced parking profile (p. 354) as a good way to jump-start their education and participate in the bigger picture.
Assumptions, guidelines, and standards can be re-examined with the question "Why?" and revised based on sound methods and a mechanism to self-correct.
The simple question "Why?" is a powerful tool for traffic engineers to reform their education and methods, as Marshall encourages, "Keep asking why we do what we do. Keep asking why those using our streets do what they do. Once we start answering those why questions--and connect the dots between what we do as traffic engineers and what they do as road users--I know we can do better. We can be better." (p. 371).
Marshall illustrates how traffic engineers can use structured, sound methodologies made in good faith. He quotes a rational process applied to traffic calming (from Reid Ewing's 2003 article, "Legal status of traffic calming," in Transportation Quarterly. 57. 11-23.):
1. Document the problem;
2. Consider options and develop intervention;
3. Pilot and test the intervention;
4. Follow up and evaluate the intervention; and
5. Use engineering judgment as an option (p. 260).
Marshall again emphasizes: "The reality is that our current guidelines aren't what is stopping traffic engineers from building safer streets. There is plenty of flexibility built into the guidelines--that is, if traffic engineers are willing to use it." (p. 261). The idea is to "better integrate transportation infrastructure with the interests of the community during the design process... guidelines blindly followed will not protect against liability" (p. 261). Marshall warns: "To the risk-averse traffic engineer, it may be time to rethink your relationship with liability. The so-called standards might not save you" (p. 261).
Looking over Marshall's coverage of traffic engineering and other work, a bigger picture emerges: traffic engineers could improve their work by re-examining assumptions about transportation, understanding how people interact with transportation infrastructure and choices, and cooperating with others to work toward public goals.
Marshall's point is "that too many of our engineering solutions treat people like inanimate carbon rods" (p. 53), and this suggests that traffic engineering education should not ignore the human element. Marshall calls for continued technical excellence but better assumptions and practices. He does not call for engineering "by committee." However, he asks for the recognition that human beings inhabit a landscape outside of transportation and react to built transportation infrastructure for purposes and in ways, if understood better, could inform the work of traffic engineering and related fields.
Engineers need to move out of silos of study and practice, the tendency towards technofuturism, and the insistence on the slogan "engineering, education, and enforcement" as a way to address all problems and hide responsibility. Engineers can avoid tunnel vision fixated on automobiles only.
Susan Handy, in Shifting Gears: Toward a New Way of Thinking about Transportation (2023), describes shifts in core ideas about transportation engineering. She re-examined a prevailing superficial understanding of speed, vehicles, capacity, separation, hierarchy, separation, control, and technology to suggest rethinking basic assumptions about freedom and mobility (Handy, pp. 227-229). She asks, "Could we be at a tipping point toward a new way of thinking?" (Handy, p. 227). These dramatic shifts have emerged from a gradual recognition of the folly of "improving efficiency narrowly defined" to a rethinking of the relationship among people, destinations, and transportation modes so that "congestion [is] less relevant to people's lives." (Handy, p. 229). Handy claims that "focusing on accessibility--in place of rather than in conjunction with mobility--is a way to solve our congestion problem" (Handy, p. 229).
Charles Marohn, in Confessions of a Recovering Engineer: Transportation for a Strong Town (2021), made a stunning admission as a professional engineer: "I designed and built dangerous stroads [an unproductive amalgam of streets and roads], all while convincing myself that I was making things safer... I joined with others in my profession to ridicule and marginalize those who disagreed with the standard industry approach" (Marohn, pp. 231-232). In his book, he gives his account as a professional engineer and city planner and questions the assumptions of his profession. He calls for overturning the orthodoxy of traffic volume and speeds as the ultimate in transportation engineering. Marohn suggests that traffic engineers must get input from the public and elected officials on design decisions and priorities so that engineers, using "value-free" descriptions, can perform their technical work (Marohn, pp. 13-14). By cooperating and collaborating, traffic engineers can participate in the bigger picture of re-examining assumptions and practices of transportation.
Other authors have examined how a better understanding of human habitation and land use can inform transportation designs. In his book, The 15-Minute City: A Solution to Saving Our Time and Our Planet (2024), Carlos Moreno describes the simple concept, millennia old, of living closer to your essential needs to gain more useful time to live your life, have more personal freedom, and enjoy meaningful interactions with your family, friends, and others. Moreno draws on concepts including the field of time geography to study the "geographical, spatial, and temporal links in human behavior" (Moreno, p. 48). The recognition of distance as a factor in the simple Physics 101 equation of distance = rate * time could dramatically reverse the emphasis on high speeds for traffic movement.
Urbanists and cultural critics have long examined how people use cities (Reader 2004). Happiness plays a role (Montgomery 2013). Public transit plays a role (Marshall 2001; American Public Transportation Association, "Benefits of Public Transportation"; Litman, Todd., "Responding to Public Transit Criticism"; Litman, Todd., "Evaluating public transit benefits and costs"; American Public Transportation Association, "Economic Impact Of Public Transportation Investment"). Parking and land use play a role (Shoup 2005, 2011; Shoup 2018; Mepham 2024; Willson 2013; Knowles 2023; Grabar 2023). Zoning plays a role (Gray 2022; Ross 2014; Leinberger 2008). Economics plays a role (Florida 2004; Glaeser 2011; Florida 2017). Architecture and urban planning play a role (Talen 2013, Kunstler 1993, 2002; Leinberger 2008; Langdon 1994; and more). Marshall's accomplishment in his book has been to reveal traffic engineering faults but also a way toward correcting those faults by a broader understanding of the role of transportation in human civilization.
Marshall states, "We can't imagine a world without cars. This book isn't meant to imagine a world without them" (p. 7). Marshall never suggests eliminating cars in this book to solve transportation problems. However, I question the statement, "We can't imagine a world without cars" (p. 7). We have thousands of years of recorded human history before 1915 showing numerous human settlements with no (or much fewer) cars, including mass transit in the late 19th century and examples of co-existing modes of transportation, including with early automobiles, into the early 20th century. Also, there are multiple examples of car-free city areas, people's lives, and many imaginative concepts of car-free towns and cities. I question the assumption that our contemporary life or economy requires car use by everyone. Some people consider any discussions of options for people to live car-free as a "war on cars" or the hyperbole that "they want to ban cars." We can see that car-free sections of cities and, most importantly, car-free people (see also Zivarts 2024) have existed in our past and do exist in our present world. To gain from this knowledge, we can revisit these histories and accounts, learn from them, and consider how car-free areas and car-free people play roles in cities and regions.

V. I see a bigger picture encompassing this book's coverage.

After reflecting on this book, I better understand how faults in traffic engineering have developed from assumptions and practices. These faults have led to oversized automobile transportation infrastructure that has propped up the role of the automobile as the focus of transportation design and land use decisions. As automotive technology has advanced, traffic engineering has joined in to boost technological determinism's role in shaping transportation policies for cities and regions. Marshall's explication of traffic engineering faults provides a fuller explanation of why there has been a reduction of people-oriented places and the elimination of multiple choices for transportation modes in many areas. As Marshall outlines, a way forward is for traffic engineering to reform itself and participate in building infrastructure that helps people and communities thrive.

Based on Marshall's invitation to "Make sure we see the bigger picture" (p. 372), I offer my bigger picture points about transportation:

Marshall's examination of traffic engineering reveals a century of mistakes culminating in a landscape warped around automobility.
The biggest lesson I gained from this book is that many traffic engineers have been working on plans based on poorly made assumptions, spotty research, and ineffective methods. What is worse, they have used assertions of questionable standards and have defended their practices by gaslighting the public, secure in the knowledge that they need not fear being held responsible. With the power this engineering work has had, highways and roads have grown to be the spines that have reworked the landscape of the world to a place of car dominance, environmental and health hazards, and reduced options for living choices.
Marshall's book explains how traffic engineers work. Megan Kimble, in her book City Limits: Infrastructure, Inequality, and the Future of America's Highways (2024), documented how people have struggled in opposing freeway expansions and their frustration with feelings of not being heard or respected. Marshall's book explains, from the traffic engineer's viewpoint, why people may feel this way during the public comment period for highway projects. I have experienced this in providing my comments about highway expansion plans to our metropolitan planning organization. I heard the officials at a meeting characterize public transportation as for the "poor and uneducated," implying its use as a transportation mode should be minimized. I heard other members of the public on a comment session on a Zoom call express a feeling of gaslighting during these public comment sessions.
In the larger picture, the outcome of faulty traffic engineering has led to maladaptive building practices and alterations of the landscape. While automobiles have played a beneficial role, this role grew to be outsized. For example, the US Interstate Highway System provides a vital link for transportation and trucking, but its incursion into cities created historic dislocations (Kay 1997; Kimble 2024) and inequities (Davis 2023). Critics and authors describe the process of suburbanization (Kay 1997; Duany et al., 2000; Solomon 2003; Hirschhorn 2005; Wasik 2009; Ross 2014) and the increase of car dependency and the loss of urban fabrics for walking and public transit in cities (Kenworthy, 2017; Newman & Kenworthy, 1999, 2015, 2021; Newman et al., 2016).
The tremendous costs of the over-built automobile infrastructure created by faulty traffic engineering methods weigh down alternative funding possibilities. Many drivers remain ignorant of these costs and don't acknowledge that drivers do not pay the full costs of roads, nor do highways pay for themselves with user fees. Further, this excessive and oftentimes hidden support for cars, car storage, and car dependency has warped the landscape and policy discussions so much that many people cannot and do not want to see a way out of it.
The result is that trillions of dollars have been spent on unnecessary automobile transportation infrastructure from freeways to parking lots, most of which sits unused much of the time, incurring enormous costs for maintenance, upkeep, and relentless expansion plans. In the book, Sprawl Kills: How Blandburbs Steal Your Time, Health, and Money (2005), Joel S. Hirschhorn helps show how various groups oppose alternatives to this automobile dominance.
Carlos Moreno, in The 15-Minute City: A Solution to Saving Our Time and Our Planet, traces the 20th-century conception of the city as a machine to the Athens Charter of 1933 as a crucial point in urban development (Moreno, p. xvii, forward by Jan Gehl). The concept of the city as a machine separated city functions and demoted public space and walking. This corresponded to, as Norton (2008) describes, the rise of motordom and the city as a platform for automobile travel. These trends reduced the emerging urban fabrics for transit (Newman & Kenworthy, 2016). Marshall's book explains the traffic engineering power underpinning the rise of this car dominance. In 1998, European urbanists stated a new Athens Charter of City Planning, "stating firmly that the people and functions of the city should no longer be separated" (Moreno, p. xix, forward by Jan Gehl). This recognition of integrated cities and a rejection of the assumption that the city was a machine may show a tipping point in practices to embrace the city as a setting for people to thrive.
A cross-disciplinary field of study involving human habitation, mobility, transportation modes, and access could support improved living choices and transportation options.
The separation of the areas of study that address how people live and move around to access resources prevents traffic engineers and others from seeing the bigger picture of transportation. Traffic engineers could gain insight by understanding how transportation infrastructure touches land use and geography, architecture, urban planning, the environment, human health, equity concerns, qualities of livability and habitation, and productive work and prosperity for people and communities.
Authors have noted the conflict between mobility and access in understanding the purpose of transportation (Handy 2023, pp. 73-79; Marhohn 2021, pp. 77-99). This conflict plays out in road designs; Marohn uses the example of the differences among streets, roads, or their unproductive amalgam, stroads (Marhohn 2021, p. 29). The lack of coordination among concepts of mobility, access, and land use leads to transit infrastructure which is insensitive to people's needs and warped by latent engineering faults.
The tangled conflict between mobility and access plays out in public transit that is poorly poised to thrive because it lacks transit-oriented development (access) and the best use of specific transit modes for different geographies and densities (mobility). (See also: Berman 2023 and Spieler 2018). Transit is degraded in service when people have distant, difficult, or complex travel from their homes, work, and destinations to and from transit stops. Transit suffers from oversupplying parking for automobiles on a free, underpriced, or tolerated illegal basis (see: Parking Reform Network) because parking favors car travel and devalues walking and other modes. Further, the prejudice of ignoring rider experience of modes--for example, favoring "nimble" buses versus considering streetcars which have distinct advantages--reduces transit choices. More importantly, these prejudices and imbalances play out in vastly different funding and political support for different forms of transportation.
Our transportation infrastructure should not be designed by a committee but by people who have a solid foundation in empirical evidence, logic, and the purpose of transportation, as well as empathy for people. It will require engineers and planners who are capable of cross-disciplinary cooperation, collaboration, and communication so that their ideas can help others without arrogance, condescension, or misleading statements.
The axioms of transportation must be restated.
Branches of mathematics have axioms. For example, plane geometry states an axiom about the distance between two points, which differs from what spherical geometry states. These axioms, stated upfront, lead to different systems of geometry. Axioms are assumptions taken as true and used as a basis for further reasoning in proving theorems.
The mistake Marshall traces in traffic engineering is that there are assumptions, but they are considered so "obvious" that they are often unstated and, with their consequences wholly accepted, no matter how counter to common sense or empirical results. Definitions, too, lack clarity. Marshall's classroom exercise, asking "What is transportation?" demonstrates a need to define the purpose of transportation as a foundation for the profession.
I define transportation as a means of providing mobility for people to access resources, places, and their community to achieve goals for living with thriving outcomes for everyone's health, equity, livability, and prosperity. Inherent in this definition is that mobility and access work together--transportation infrastructure works with land use for a purpose: to enable people to thrive, both as individuals and as communities. Further, mobility includes more than just a possible ride on a vehicle; it is a total pathway for all abilities, from origins to destinations, including from home to locations for work, resources, and transit stops. Finally, the outcomes must work for everyone--for drivers of automobiles, nondrivers, riders of bicycles, people walking, people using assistive devices, and for all community members, young and old, rich and poor.
Traffic engineers should recognize that transportation infrastructure should serve people and communities and not the other way around.
All of the reasons for transportation infrastructure should relate to community goals and ways for people to thrive. Speed, capacity, and other engineering quantities play a role in accomplishing this, but the technologically deterministic focus on quantities that measure the movement of cars as the end goal leads to unsafe and ineffective choices for mobility and access to resources.
Some people express considerable anxiety over the idea that automobiles may be demoted in transportation importance in any way. Some might call any reform of traffic engineering a "war on motorists" (Walker 2023). This defensive viewpoint demonstrates the impact of the upside-down view that the automobile is the apex of transportation and the whole point of community life--the automobile as the god of the "religious cult" critique that Marshall raises (p. 74).
Still others claim that once made self-driving, the automobile will erase the need for "old-fashioned" considerations for transportation modes other than cars, including public or active transit. However, as Peter Norton, in his book Autonorama: The Illusory Promise of High-Tech Driving (2021), has shown, promoting autonomous vehicles as the solution to transportation problems has never been about technology nor the future--but about extending car dependency: "AVs are no solution to mobility problems... promoters of automated driving are less interested in human mobility than in preserving car dependency" (Norton, p. 226). Norton provides a succinct statement of his main point on page 219:
"Predictions that automated driving will make car dependency work have been failing for sixty years. Numerous innovations have offered important safety and efficiency benefits, but nothing has come close to solving the problems that make ubiquitous driving hazardous, spatially inefficient, unsustainable, and inequitable" (Norton, p. 219).

The fantasy world of technofuturistic or self-driving cars does not provide a total transportation solution because it claims many resources and costs, demotes the agency of people in choosing different ways of living, devalues modes of transit other than cars, warps the landscape further around automobile infrastructure, places people subservient to technology, and uses a method of rhetorical closure to extend car dependency.
Self-driving cars are presented as the gods (end-goal) of transportation every bit as driver-driven cars are today. Moreover, many hyped "pod-like" transportation gadgets, a forerunner of the autonomous vehicle hype, are regularly proposed as a way to detract from competent mass transit systems that have been proven in thousands of places around the world for over a century (buses, streetcars, bicycling, and walking for example).

Many people face a lack of transportation options and affordable places to live in the world's many different landscapes, geographies, and densities. Traffic engineering can help by reworking and rebalancing our transportation infrastructure and land use with new priorities, starting with the basics: people matter.