This book s title has two parts, Roadway Human Factors and From Science To Application. The first describes its major goal: to analyze driver behavior, especially the causes and avoidance of collisions. In most general terms, the goal is largely to answer a single question: Why didn t the driver respond sooner? The cause of most collisions lies in the answer.
The book s perspective is psychological. It views roadway events through the eyes of the driver. This contrasts with the third-party god s eye view that appears in accident reconstruction diagrams and other analyses which are primarily based in physics and cookbook science. Physics cannot be ignored, but roadway events can only be explained by examining driver psychology. Drivers act based on their perceived reality which differs from the physical reality of the accident reconstruction diagram.
The second part announces its method: the application of scientific research. Specifically, the science in question is experimental psychology. Much of this book reads like an introductory text on experimental psychology, albeit with a distinctly applied slant. This is necessary. There are frequent misunderstandings about the definition of human factors. It is best described as a branch of experimental psychology. Human factors applies experimental psychology data to guide the design of objects and environments so that they that fit human abilities and are easy and safe to use.
This book s underlying thesis is that knowledge of the science is a necessary but not sufficient condition for understanding roadway human factors. The key word in the title is From because there is a catch-22. Controlled research has inherent characteristics which differ from real-world conditions. Scientific research is generally conducted in highly simplified and artificial situations with unrepresentative subjects and drivers. Scientific research data cannot then be directly applied to the real-world. The step from science to application is far greater than many imagine, probably because there are so few who are well versed in both.
The book also introduces areas of science that are unfamiliar to most who investigate collisions. Ecological optics is a discipline of perceptual psychology that is key in understanding vehicle guidance and collision avoidance. Visual psychophysics is the psychological science that underlies visibility and all other sensory judgments. Operant learning is the psychological science of adaptability and behavior change based on the consequences of action. The book also introduces more specific concepts that are important but seldom figured into collision analysis. These include notions such as affordances and action boundaries, system tolerances, crowding, and response conflicts.
The first seven chapters cover basic experimental psychology topics. In each of these chapters, however, the topic s relevance is highlighted by the discussion of how it would be applied to roadway human factors. Chapter 2 discusses the most basic human factors, the ability to sense and to adapt to the world. It describes how viewers sense the world and make yes/no and magnitude judgments about whether anything is out there. It also explains the basic mechanism of learning and adaptation that shapes driver behavior and often leads to high risk taking. Chapter 3 covers the basic physical properties of light and their weak relationship to the fundamental sensations of brightness and color that provide the raw material for perception.
Chapters 4 and 5 switch to visibility. The chapters are detailed how-to discussions on determining contrast threshold, and hence when a roadway object would be visible. Chapter 4 reviews the physical calculations needed to determine contrast, while Chapter 5 outlines the methods for calculating contrast threshold. Chapter 6 explains human information processing and the factors that determine whether a driver will consciously perceive an object, such as a vehicle or a pedestrian. It also discusses driver cell phone distraction and driver aging as examples about the perils of applying research data to predicting real-world events. Chapter 7 describes the perception of space and motion, which drivers use to predict whether a conflict and potential collision is imminent.
The final four chapters apply concepts and data from the previous material to road collisions. Chapters 8 and 9 analyze vehicle collisions into two fundamental geometries based on the driver s main task. Chapter 8 examines longitudinal geometries, such as rear-end and head-on, where the approaching vehicle moves in depth straight toward the eye. The primary driver task is to make motion-in-depth judgments that predict future vehicle locations. In longitudinal geometries, detection is usually easy, so the most common collision cause is motion-in-depth misjudgment. Chapter 9 discusses lateral geometries, where the approaching vehicle is on a crossing path. The driver must detect the approaching vehicle and judge whether there will be a conflict at an intersecting point. In lateral geometries, motion prediction is easy (or at least easier) but detection is more difficult. Detection failure is then the major collision cause. Examples of real collisions demonstrate these principles.
Chapter 10 examines pedestrians and bicycles, whose collisions resemble those discussed in the preceding chapters but with some added issues. There is a short discussion of ways to reduce the number of these collisions. Chapter 11 ends the book with a review of perception-response time, the most widely misunderstood and misused concept in collision analysis. It is the area where scientific data are most egregiously misapplied and where nonscientists (and some scientists) make their greatest mistakes.