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2024 | Book

# An Introduction to Traffic Flow Theory

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Book Series : Springer Optimization and Its Applications

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This second edition of An Introduction to Traffic Flow Theory adds new material in several chapters related to advanced technologies including autonomy, the use of sensors and communications, and particularly congestion mitigation solutions that leverage connected and autonomous vehicles (CAVs). It also includes a new chapter that briefly outlines several mathematical analysis techniques commonly used in traffic flow theory, aiming to introduce students to some of the most frequently used tools available for traffic operational-related analysis. This new edition also includes several updates related to the most recent versions of the Highway Capacity Manual and the Green Book. This textbook is meant for use in advanced undergraduate/graduate level courses in traffic flow theory with prerequisites including two semesters of calculus, statistics, and an introductory course in transportation. The text would also be of interest to transportation professionals as a refresherin traffic flow theory or as a reference. Students and engineers of diverse backgrounds will find this text accessible and applicable to today’s traffic issues.

This text provides a comprehensive and concise treatment of the topic of traffic flow theory and includes several topics relevant to today’s highway transportation system. It provides the fundamental principles of traffic flow theory as well as applications of those principles for evaluating specific types of facilities (freeways, intersections, etc.). Newer concepts of Intelligent transportation systems (ITS) and their potential impact on traffic flow are discussed. State-of-the-art traffic flow research, microscopic traffic analysis, and traffic simulation have significantly advanced and are also discussed in this text. Real-world examples and useful problem sets complement each chapter.

#### Part I

##### Chapter 1. Modeling the Motion of a Single Vehicle
Abstract
The movement of a single vehicle is a fundamental building block in traffic modeling. A single vehicle can significantly impact the performance of a traffic stream. Consider an on-ramp vehicle entering a busy freeway at a low speed: it can cause freeway mainline vehicles to abruptly change lanes, which – for the right amount of traffic – may lead to severe congestion and stop-and-go traffic. Consider also a slow-moving truck at the front of a long line of vehicles traveling behind it with no passing opportunities: the performance of this truck significantly affects the speed and travel time of the following vehicles. Understanding the characteristics, performance, and movement of each vehicle allows us to model groups of vehicles and estimate the performance of the traffic stream. Furthermore, the movement of individual vehicles allows us to develop better highway design and traffic control solutions. For example, understanding the acceleration and deceleration constraints of various vehicle types can help us design more effective passing zones and allocate appropriate yellow and all-red intervals at signalized intersections.
##### Chapter 2. Modeling Vehicle Interactions and the Movement of Groups of Vehicles
Abstract
Chapter 1 discussed the movement of an individual vehicle and provided the equations of motion assuming there are no other vehicles around. This chapter examines the interactions between vehicles, which is at the heart of traffic flow theory. It is these interactions that produce the observed traffic operational conditions, including crashes and congestion. Traffic operational characteristics of interest include capacity (i.e., the maximum amount of traffic that can pass through a point or section in vehicles or other units of traffic per unit time), prevailing speed (i.e., the speed at which the facility operates under a given set of prevailing conditions, including the demand, the highway design, etc.), delay, and travel time. These characteristics are discussed in more detail in Part II.

#### Part II

##### Chapter 3. Flow, Speed, and Density and Their Relationships
Abstract
Flow, speed, and density are the three primary characteristics of traffic and are used to describe various aspects of operations of a highway facility. When describing and assessing traffic operations, we are often concerned with the movement of a group of vehicles, or the traffic stream, rather than the movement of each vehicle. In those cases, it is more convenient to describe traffic operations in terms of macroscopic measures of traffic.
##### Chapter 4. Capacity
Abstract
How much traffic can a facility carry? This is one of the fundamental questions designers and traffic engineers have been asking since highways were constructed. The term “capacity” has been used to quantify the traffic-carrying ability of transportation facilities. The value of capacity is used when designing or rehabilitating highway facilities to determine their geometric design characteristics such as the desirable number of lanes; it is used to design the traffic signalization schemes of intersections and arterial streets; it is used in evaluating whether an existing facility can handle the traffic demand expected in the future; it is also used in the operations and management of traffic control systems (ramp metering algorithms, congestion pricing algorithms, signal control optimization, incident management, etc.).
##### Chapter 5. Measuring Mobility: Quality, Quantity, Utilization, and Accessibility
Abstract
The previous two chapters discussed the fundamental traffic stream parameters and capacity, which provided the fundamental components for understanding traffic stream performance and for developing models to replicate the operations of traffic streams. For practitioners and policymakers, it is most important to be able to use valid traffic flow models to extract suitable performance measures. Such performance measures are used to evaluate traffic operational performance and select the best alternative for implementation. Therefore, they play a very important role in selecting the projects to be deployed. But what are these performance measures and how should we select the most suitable one(s) for a given situation?

#### Part III

##### Chapter 6. The Highway Capacity Manual (HCM) and Its Methods
Abstract
The Highway Capacity Manual (HCM) is a major reference document used in traffic analysis throughout the United States and worldwide. The HCM has been providing techniques for estimating capacity and assessing the traffic operational quality of transportation facilities for over 70 years. It is published by the Transportation Research Board of the National Academies of Sciences, Engineering, and Medicine and provides analytical tools for evaluating various types of transportation facilities such as freeways, arterials, and intersections. Since its first publication in 1950, it assists transportation professionals with traffic engineering decisions, highway design considerations, and transportation planning estimates. Through all its editions, the role of the HCM has been to provide uniform standards related to:
##### Chapter 7. Analytical Models and Techniques
Abstract
Traffic models can be very useful in the enhancement of complex transportation systems, as well as in their management and evaluation. They can help in the design and operations of traffic systems since they can predict traffic operational conditions at some time in the future under various sets of design, traffic, and control characteristics. Traffic engineers and designers can make decisions regarding facility modifications or traffic management improvements based on the expected impact of those improvements on the transportation system. Traffic models can also help in the evaluation of existing systems and in the development of priorities for improvement. Some mathematical models are based on theoretical principles. For example: Flow = Speed × Density is a mathematical model based on the fundamental principles of traffic flow. On the other hand, empirical models are those based on field observations (empirical observations) rather than on relationships that can be mathematically described. Empirical models predict how a system behaves rather than explaining how its components interact. Empirical models can be useful when the mathematical relationship is unknown or difficult to express. Examples of empirical models are the traffic stream relationships discussed in Chap. 3.
##### Chapter 8. Simulation Modeling
Abstract
Simulation is generally defined as an imitation of a system or a process, and computer simulation is the replication of a system or a process on a computer. Simulation has been used in many fields to understand the interactions between system components or evaluate alternative designs. It is routinely used in various and very diverse environments, including the training of pilots using flight simulators, weather prediction, the design of communications networks, entertainment (e.g., video games).

#### Part IV

##### Chapter 9. Freeways
Abstract
Freeways are defined as those facilities that afford uninterrupted flow of traffic, i.e., there is full access control. Control of access refers to public access rights from properties along the freeway; access to freeway facilities is allowed only through selected public roads, typically on- and off-ramps [1]. Thus, freeways generally operate at higher speeds and higher capacities than urban arterial streets or local roadways.
##### Chapter 10. Signalized Intersections and Arterials
Abstract
Signalized intersections operate with the assistance of a traffic signal, and they cyclically assign the right-of-way to a movement or a combination of movements. Ideally, the amount of time assigned to each combination of movements minimizes the travel time and delay and/or the number of stops in the network and allocates capacity optimally. An arterial is a highway facility with a series of signalized intersections along its length, while an urban network or a surface street network consists of a group of interconnected arterials and side streets.
##### Chapter 11. Unsignalized Intersections
Abstract
Unsignalized intersections are those where at least one of the movements is controlled by a STOP or a YIELD sign. Operations of such facilities require the drivers on the controlled movements (usually referred to as minor movements) to judge the size of the gaps along the major (or uncontrolled) street and select a suitable one to cross, or to merge into.
##### Chapter 12. Interchanges and Alternative Intersection Designs
Abstract
Interchange ramp terminals provide connections between various types of highways (arterial-freeway, freeway-freeway, arterial-arterial). Alternative intersection designs are innovative configurations that have the potential to improve operations by rerouting certain movements. The first part of this chapter presents examples of interchange configurations, discusses traffic operational effects of interchange characteristics and signalization for two-intersection interchanges, and summarizes the HCM7 methodological framework for these types of facilities. The second part discusses traffic operations and the HCM7 methodology for alternative intersections.
##### Chapter 13. Two-Lane Highways
Abstract
Two-lane highways, which have one lane per direction, are unique operationally since they may allow passing using the opposing traffic stream. According to the US Federal Highway Administration [1], two-lane highway facilities represent about 97% of the total highway system and more than 65% of the total nonurban vehicular travel in the United States. Hence, two-lane highways provide most of the primary interurban highway networks and are the basis of the secondary highway and collector networks. Figure 13.1 provides a sketch of a two-lane highway.
##### Chapter 14. Highway Networks
Abstract
This chapter discusses the operational evaluation of a highway system considering both freeways and arterials. Previous chapters have considered each of those facilities as an isolated system. However, when congestion occurs and queues spill back into a facility, the analysis should consider the entire freeway-arterial system (the concept is similar to the analysis of freeway systems discussed in Chap. 9, when queues spread to upstream segments). The first section of this chapter discusses spillback from an arterial to a freeway, and the second section examines the impact of spillback from a freeway to an arterial. The last section discusses the performance measurement framework used in the HCM7 to assess highway networks.
##### Backmatter
Title
An Introduction to Traffic Flow Theory
Author