Transportation Engineering: A Practical Approach to Highway Design, Traffic Analysis, and Systems Operation 1260019586, 9781260019582

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Transportation Engineering

About the Author Beverly Thompson Kuhn, Ph.D., P.E., PMP, is a Senior

Research Engineer and Division Head with the prestigious Texas A&M Transportation Institute (TTI), which is part of the Texas A&M University System. She is an expert in the area of transportation systems management and operations and the application of research results to improve traffic operations. She has taught introductory transportation engineering courses at both Texas A&M and Penn State University and has authored numerous papers and publications, including chapters in McGraw-Hill's Handbook of Transportation Engineering, and is an active member of the Transportation Research Board (TRB) and the Institute of Transportation Engineers (ITE).

Transportation Engineering A Practical Approach to Highway Design, Traffic Analysis, and Systems Operations Beverly T. Kuhn, Ph.D., P.E.

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Copyright© 2019 by McGraw-Hill Education. All rights reserved. Except as permitted under the United States Copyright Act of 1976, no part ofthis publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher. ISBN: 978-1-26-001958-2 MHID: 1-26-001958-6 The material in this eBook also appears in the print version of this title: ISBN: 978-1-26-001957-5, MHID: 1-26-001957-8. eBook conversion by codeMantra Version 1.0 All trademarks are trademarks of their respective owners. Rather than put a trademark symbol after every occurrence of a trademarked name, we use names in an editorial fashion only, and to the benefit ofthe trademark owner, with no intention of infringement of the trademark. Where such designations appear in this book, they have been printed with initial caps. McGraw-Hill Education eBooks are available at special quantity discounts to use as premiums and sales promotions or for use in corporate training programs. To contact a representative, please visit the Contact Us page at www.mhprofessional.com. Information contained in this work has been obtained by McGraw-Hill Education from sources believed to be reliable. However, neither McGraw-Hill Education nor its authors guarantee the accuracy or completeness of any information published herein, and neither McGraw-Hill Education nor its authors shall be responsible for any errors, omissions, or damages arising out ofuse ofthis information. This work is published with the understanding that McGraw-Hill Education and its authors are supplying information but are not attempting to render engineering or other professional services. If such services are required, the assistance of an appropriate professional should be sought. TERMSOFUSE This is a copyrighted work and McGraw-Hill Education and its licensors reserve all rights in and to the work. Use of this work is subject to these terms. Except as permitted under the Copyright Act of 1976 and the right to store and retrieve one copy of the work, you may not decompile, disassemble, reverse engineer, reproduce, modify, create derivative works based upon, transmit, distribute, disseminate, sell, publish or sublicense the work or any part ofit without McGraw-Hill Education's prior consent. You may use the work for your own noncommercial and personal use; any other use of the work is strictly prohibited. Your right to use the work may be terminated if you fail to comply with these terms. THE WORK IS PROVIDED "AS IS." McGRAW-HILL EDUCATION AND ITS LICENSORS MAKE NO GUARANTEES OR WARRANTIES AS TO THE ACCURACY, ADEQUACY OR COMPLETENESS OF OR RESULTS TO BE OBTAINED FROM USING THE WORK, INCLUDING ANY INFORMATION THAT CAN BE ACCESSED THROUGH THE WORK VIA HYPERLINK OR OTHERWISE, AND EXPRESSLY DISCLAIM ANY WARRANTY, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. McGraw-Hill Education and its licensors do not warrant or guarantee that the functions contained in the work will meet your requirements or that its operation will be uninterrupted or error free. Neither McGraw-Hill Education nor its licensors shall be liable to you or anyone else for any inaccuracy, error or omission, regardless of cause, in the work or for any damages resulting therefrom. McGraw-Hill Education has no responsibility for the content of any information accessed through the work. Under no circumstances shall McGraw-Hill Education and/or its licensors be liable for any indirect, incidental, special, punitive, consequential or similar damages that result from the use of or inability to use the work, even if any of them has been advised of the possibility of such damages. This limitation of liability shall apply to any claim or cause whatsoever whether such claim or cause arises in contract, tort or otherwise.

Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xi xiii

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Transportation Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 The Surface Transportation System . . . . . . . . . . . . . . . . . . . . . . . 1.4 The Transportation Profession . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Glossary of Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 2 2 10 13 13 13 14

2 Human Factors and Geometric Design . . . • . . . . . . . . • . . . . . . . . • . . . 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 User Characteristics and Human Factors . . . . . . . . . . . . . . . . . . 2.2.1 Human Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 Driver Characteristics and Limitations . . . . . . . . . . . . . . 2.2.3 Decision Making . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Driver Expectancy, Consistency, and Positive Guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 Design Policies and Standards . . . . . . . . . . . . .. .. . . . . . . 2.3.3 Speed . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . 2.3.4 Sight Distance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Cross Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Horizontal Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.1 Superelevation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.2 Side Friction Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.3 Minimum Radius . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.4 Sight Distance on Horizontal Curves . . . . . . . . . . . . . . . . 2.6 Vertical Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.1 Grades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.2 Crest Vertical Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.3 Sag Vertical Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7 The Project Development and Design Process . . . . . . . . . . . . . .

17 17 17 18 21 23 25

1

25 26 28 29 39 42 42 43 47 48 50 51 51 56 58

y

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Contents

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2.8 Case Studies .......................................... . 2.8.1 Design for Safety Partnership-California Department of Transportation (Caltrans) ....................... . 2.8.2 Construction Traffic Management Strategies-Ohio Department of Transportation (ODOT) .... ......... . 2.8.3 Construction Practices-Illinois Department of Transportation (IDOT) ......................... . 2.9 Summary .................................. ......... .. . Glossary of Acronyms ....................................... . Exercises ................................................... . References ........................................ ......... .

61

Traffic Flow Theory and Capacity ............................ . 3.1 Introduction ..................................... ..... . 3.2 Traffic Operating Conditions ............................ . 3.2.1 Uninterrupted Flow ............................. . 3.2.2 Interrupted Flow ........................... ..... . 3.2.3 Undersaturated Flow ............................ . 3.2.4 Oversaturated Flow .............................. . 3.2.5 Queue Discharge Flow ...................... ..... . 3.3 Traffic Flow Characteristics ............................. . 3.3.1 Flow ........................................... . 3.3.2 Speed .................................... ...... . 3.3.3 Density ........................................ . 3.3.4 Occupancy and Related Parameters ................ . 3.3.5 Speed-Flow-Density Relationship ............ ...... . 3.4 Traffic Analysis Tools .................................. . 3.5 Roadway Capacity .................................... . 3.5.1 Capacity .................................. ..... . 3.5.2 Conditions Impacting Capacity .................... . 3.5.3 Level of Service ................................. . 3.6 Capacity of Uninterrupted Flow Facilities ........... ..... . 3.6.1 LOS, Density, Speed, and Flow Rates ............... . 3.6.2 Computing LOS and Capacity for a Basic Freeway Segment ................. ..... . 3.7 Capacity of Interrupted Flow Facilities ................... . 3.7.1 Capacity and LOS of a Signalized Intersection ....... . 3.8 Case Studies .................................... ...... . 3.8.1 SHRP2-Capacity Solutions ...................... . 3.8.2 Roadway Improvements and Operational Capacity 3.9 Summary ....................................... ...... . Glossary of Acronyms ....................................... . Exercises ................................................... . References

67 67 67 68 69

61 62 62 63 63 63 65

70 71

72 72 72

75 77

77 78 80 83 84 85 85 86 87 87 92 93

100 100 101 102 102 103 106

CO I I e I ts 4

5

Traffic Control ............................................. . 4.1 Introduction ..................................... ..... . 4.2 Traffic Control Devices ................................. . 4.2.1 Definition, Purpose, and Principles ................ . 4.2.2 Design .................................... ..... . 4.3 Traffic Signals ......................................... . 4.3.1 Traffic Signal Warrants ........................... . 4.3.2 Traffic Signal Operations .................... ..... . 4.3.3 Performance-Based Approach to Signal Operations ............................. . 4.3.4 Traffic Signal Timing Basics .................. ..... . 4.4 Regional Traffic Signal Operations Programs .............. . 4.5 Case Studies .......................................... . 4.5.1 Traffic Signal Management Plan-Utah ....... ...... . 4.5.2 Regional Traffic Signal Operations Program-Denver, Colorado ...................... . 4.6 Summary ....................................... ...... . Glossary of Acronyms ....................................... . Exercises ................................................... . References

107

Transportation Safety •........•........•........•........•... 5.1 Introduction .......................................... . 5.2 Safety Challenges and Programs ......................... . 5.2.l Highway Safety Improvement Program .......... .. . 5.2.2 Intersection Safety ............................... . 5.2.3 Local and Rural Road Safety ...................... . 5.2.4 Pedestrian and Bicycle Safety ................... .. . 5.2.5 Roadway Departure Safety ....................... . 5.2.6 Roadway Safety Data Program .................... . 5.2.7 Speed Management ........................... ... . 5.3 Vulnerable Populations ................................ . 5.3.1 Motorcycles ..................................... . 5.3.2 Children ..................................... .. . 5.3.3 Highway Workers ............................... . 5.3.4 Distracted Drivers ............................... . 5.4 Planning for Safety .................................. .. . ....................... . 5.5 Safety Performance Management 5.6 Case Studies .......................................... . 5.7 Summary .......................................... ... . Glossary of Acronyms ....................................... . Exercises ................................................... . References

151

107 107 109

111 114 114 116

120 126 140

143 143 144 146 146 147

148

151 151 152 155 158 160 164 170 171 173 175 177 178 180 180 182 182 184

184 184 185

VII

VIII

CO I le I ts 6 Transportation Planning and Demand . . . . • • . . . . . . . • • . . . . . . . • • . 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Transportation Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.1 Key Planning Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.2 Land Use and Transportation . . . . . . . . . . . . . . . . . . . . . . 6.2.3 Livability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.4 Planning for Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.5 Congestion Management Process . . . . . . . . . . . . . . . . . . . 6.3 Travel Demand Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.1 Trip Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.2 Trip Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.3 Mode Choice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.4 Trip Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4 Analysis, Modeling, and Simulation . . . . . . . . . . . . . . . . . . . . . . 6.5 Travel Demand Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6 Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Glossary of Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

189 189 189 193 194 195 197 197 199 201 207 210 212 213 214 216 218 218 219 222

Transportation Systems Management and Operations • . . . . . . . • • • 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 .2 Types of Congestion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.1 Bottlenecks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.2 Signal Tuning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.3 Work Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.4 Road Weather . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Planned Special Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.1 Traffic Incidents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Planning for Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5 Organizing for Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6 Designing for Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.7 Benefits and Costs of Operations . . . . . . . . . . . . . . . . . . . . . . . . . 7.8 TSMO in Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.8.1 Adaptive Ramp Metering . . . . . . . . . . . . . . . . . . . . . . . . . . 7.8.2 Dynamic Lane Reversal . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.8.3 Dynamic Lane Use Control/Dynamic Shoulder Use . . . 7.8.4 Queue Warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.8.5 Variable Speed Limits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.9 Managed Lanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.10 Real-Trme Traveler Information . . . . . . . . . . . . . . . . . . . . . . . . . . 7.11 Performance Measurement and Performance Monitoring 7.12 Transportation Management Centers . . . . . . . . . . . . . . . . . . . . . . 7.13 Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

225 225 226 229 230 230 231 233 234 235 237 240 240 241 244 244 245 246 247 248 249 249 252 255

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Contents

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7.14 Summary ............................................. . Glossary of Acronyms .............................. ......... . Exercises ................................................... . References ................................................. .

260 261 262 262

Emerging Transportation Topics ............................. . 8.1 Introduction .......................................... . 8.2 State of the Transportation Infrastructure ............ ..... . 8.2.1 Bridges ......................................... . 8.2.2 Roads .......................................... . 8.2.3 Transit .................................... ..... . 8.3 Livability and Sustainability ............................ . 8.4 Transportation System Resilience ........................ . 8.5 Roadway Safety ................................. ...... . 8.6 Disruptive Technologies and Transportation .............. . 8.7 Connected and Automated Vehicles ...................... . 8.8 Smart Cities 8.9 Highway Automation .................................. . 8.10 Case Studies .......................................... . Summary ............................................. ..... . Glossary of Acronyms ....................................... . Exercises ................................................... . References

267

267 268 268 270 272 274 283 286 287 289 292 295 296 300 300 301 301

Index

307

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Preface

T

ransportation-the movement of people, goods, and services in a safe and efficient manner-is a foundational component of society and has been for eons. It is essential to how we live our lives, it drives the economy in countless ways, and it often only comes to the attention of society when it fails to live up to its expectations. Millions of individuals are responsible for keeping this behemoth in working order, and they face challenges at every turn. Professionals with a broad range of skills undertake the cradle-to-grave responsibility of planning, funding, designing, constructing, operating, maintaining, repairing, retrofitting, and upgrading the entire transportation system across all modes to meet society's demands. This textbook focuses on the surface roadway network, which is one aspect of this system with which nearly all travelers across the globe are familiar. It provides information on the critical scientific principles needed to create a safe and efficient system and addresses the interrelated topics of demand and operations, which directly affect the sustainability of the surface network. It also highlights emerging topics that transportation professionals are beginning to face that could revolutionize the way we travel in the future.

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Acknowledgments

F

irst and foremost, I would like to thank my husband, Darrell Kuhn, for his unending love and support throughout my entire career and for always being a willing companion on this journey. I also thank my sons, Harrison Kuhn and Parker Kuhn, for their understanding for the many times I was away from home. I extend my thanks to all of the professors, mentors, and colleagues who have guided and supported me over the past 30 years. I would not be where I am without any of you. I would also like to thank Lauren Poplawski at McGraw-Hill for her guidance throughout the publication process. Finally, to my family and friends who have always supported me from both near and far throughout my career, I am humbled and forever grateful to be a part of your tribe.

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CHAPTER

1

Introduction 1.1

Introduction Transportation-the movement of people, goods, and services in a safe and efficient manner-is a foundational component of society and has been for eons. It contributes to the safety, security, and prosperity of global economies and is something that many individuals often take for granted. The action of getting into a car to drive to work on smooth roads with minor interruptions while arriving safely is undertaken millions of times each day without a second thought by the driver. Additionally, passengers take millions of commute trips by bus, train, bicycle, or walking, arriving at their destination without the hassle of driving themselves. Furthermore, they likely conducted business or handled personal issues via telephone along the journey if they were not driving alone in a vehicle. Consumers fill their shopping carts with products without considering how they got from the field, plant, or factory to the shelf in the store, much less how the various components originally arrived at the factory. Their online purchases arrive at their doors in only a few days and, in some cases, hours. Consumers fly around the country or the globe in comfort, passing through major airline hubs with every convenience available. However, when individuals do not have access to affordable transportation, their ability to make a living, to take care of their personal health and that of their family members, and to contribute to society is impaired. As individuals age, their ability to be independent deteriorates, making access to affordable mass transit or other means of mobility even more critical to a high quality of life. The same can be said for those with disabilities that make driving a personal vehicle impractical or impossible. Transportation is an integral part of life in today's rapidly advancing world that must be maintained in terms of affordability, flexibility, and sustainability. Transportation is essential to how we live our lives, it drives the economy in countless ways, and it often only comes to the attention of society when it fails to live up to its expectations. Millions of individuals are responsible for keeping this behemoth in working order, and they face challenges at every tum. Professionals with a broad range of skills undertake the cradle-to-grave responsibility of planning, funding, designing, constructing, operating, maintaining, repairing, retrofitting, and upgrading the entire transportation system across all modes to meet society's demands. This textbook will focus on one aspect of this system with which nearly all travelers across the globe are familiar: the surface roadway network. While surface transportation is by no means the sole mode of transportation used today, it represents the most common mode with which travelers interact on a daily basis. This text will provide information on the critical scientific principles needed to create a safe and efficient system and address the interrelated topics of demand and operations, which directly affect the

1

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Chapter One sustainability of the surface network. Finally, it will highlight emerging topics that transportation professionals are beginning to face that could revolutionize the way we travel in the future.

1.2 Transportation Engineering Merriam-Webster defines engineering as the "activities or function of an engineer" in which science and mathematics are applied to matter and energy in nature and are made useful to people. 1 Thus, within the transportation context, transportation engineering is the field of study related to planning, design, operation, and maintenance of any aspect of transportation systems and networks. It is the responsibility of transportation professionals to ensure that the complex transportation facilities, which afford mobility for people and goods, do so in a safe, rapid, comfortable, convenient, and environmentally compatible manner that is sustainable and resilient in the face of numerous challenges and threats such as natural disasters, population growth, and climate change. Transportation engineering has for decades been included as part of the discipline of civil engineering since transportation networks typically fall within the public domain. They are available for the general public, and their upkeep is typically the responsibility of public agency employees and their contractors. It is important to note that transportation engineering could be considered more of an art than a science. Professionals within the field are required to make many decisions based on society's needs and desires for mobility, and the answers are not always easy given the need to balance needs with the reality of limited resources. The identification of solutions involves the synthesis of different intellectual perspectives and scientific bases to solve transportation problems across the breadth of competing interests: technical, economic, social, and environmental in nature.

1.3 The Surface Transportation System Since the turn of the previous century, the United States has grappled with the challenge of providing convenient and safe transportation options to its citizens. Over the decades, the national policy on surface transportation has shifted from construction to sustainability as evidenced by the evolution of funding bills passed by the U.S. Congress. The following provides a brief overview of critical federal funding legislation, which has shaped the transportation system in the United States over the past century. The Federal Aid Road Act of 19162 recognized the rise of the automobile and the growing challenge of getting the farmer out of the mud. With this legislation, which was passed by President Wilson on July 11, 1916, Congress formally recognized that the government had the right to fund the construction of interstate highways under the constitutional right to regulate interstate commerce and that these facilities would be the backbone of the country's economic growth. The first federal highway funding legislation in the United States, this act addressed the inadequate roads in the country and the need for an increased federal role in funding. 2 The law required each state to establish and maintain a highway agency, employing engineering professionals to carry out federal-aid projects identified by the federal government. The law focused on rural post roads and illustrated the importance of working to enhance rural life in the United States. The Federal Aid Road Act of 1927'3 amended the 1916 act by expanding the roads eligible

Introduction

F11u11E 1.1 Vehicle stuck on a muddy roadway. (©Texas Department of Transportation [fxD01].)

for funding from rural post roads to any public road being used or which formed a connecting link with other roads. As shown in Fig. 1.1, many existing roadways beaune muddy after heavy rains, making travel virtually impOSSible. These early road acts sought to provide states with the resources to help improve the quality of these roadways so that travelers could use them under a variety of conditions. Improving these facilities would also foster interstate commerce into the future. Various forms of transportation .funding progressed over the next few decades until 1956. With the National Interstate and Defense Highway System Act of 1956,4 President Eisenhower established the interstate highway system in the United States. The law authorized the expenditure of $25 billion to construct 41,000 miles of interstate highways between 1957 and 1969. This legislation represented a .fundamental shift in the country toward a surface transportation system that .from that point forward would focus on the automobile. Eisenhower's support of the system was based on the need for economic development, congestion re.lief, improved safety, and the reduction of lawsuits involving motor vehicles.5 The interstate highways were also intended to support national defe:nse in the post-war era, though this was not the primary reason for their construction. The interstate system also helped establish uniform geometric design and construction standards that included such features as fully controlled access, design speeds, paved shoulders, and a minimum of two 12-foot travel lanes in each direction. Many of these design criteria still exist today. The shift toward an auto.mobile-centric transportation system directly impacted the pattern of community development and the transportation network into the future. For example, the interstates were frequently constructed through the rural countryside where only local roads existed previously. Figure 1.2 shows early construction on Interstate 45 (I-45) in the area north of Houston, Texas, which at the time was the rural community of Coruoe. The construction of this highway connected Houston and Dallas, greatly reducing the travel time between these cities that are over 200 miles apart. A trip that at the time took the better part of a day became only a few hours in length. The existence of such new transportation facilities in rural areas often attracted development,

3

particularly around interchanges with other major roadways and highways. Areas such as Comoe transformed. from the rural landscape of a sleepy town to a bustling suburb, as shown in Fig. 1.3. While the concept of selecting a location for an interstate facility through the rural countryside seems straightforward, alignments were often controversial at the local level. Small communities or counties did not always want to have an interstate close by, fearing that the roadway would negatively affect the small town atmosphere they enjoyed. Such local sentiment often impacted the final location of the facility by having the facility bypass the community and sometimes having a detrimental effect on the economic health of the region that rejected it. The construction of the interstate system also impacted the urban environment, as shown in Fig. 1.4. In many cities, the proposed alignment for the interstates often divided established neighbo.rhoods and created conflict between their residents and the local leade.rs.6 Some critics of the system noted that many of these facilities divided lowerincome neighhorhoods, having them bear a disproportionate burden for the progress brought by the interstate. Additionally, the interstates made the commute from outlying suburbs easier for worker&, encouraging suburban sprawl with low-density, affordable development and an ever-increasing reliance on the autom.obile as a mode of transportation. Many early mass transit services faded from the urban landscape. Air and noise

Introduction

5

F11uRE 1.5 Early roadway congestJon. (© Texas A&M Transportation Institute [TTI].)

pollution increased in the urban centers along with growing traffic congestion. In short, the interstate system likely contributed to the transportation-related problems it was intended to solve. As early as the 1960s, these new interstates were experiencing congestion, as pictured in Fig. 1.5. The commuters from the suburbs traveling to the employment centers in large cities were forced to sit in traffic on a daily basis. Such situations created the ongoing challenge to provide adequate capacity for peak period travel. Early efforts to monitor traffic on the roadway network included such.innovative strategies as the construction of towers along the roadway (see Fig. 1.6) to observe traffic behavior and to identify bottlenecks in the system. Motion picture cameras were also installed along interstate corridors to record traffic flow during congested periods. Films were then used by traffic engineers in monitoring the conditions and improving operations (see Fig. 1.7). These scenes were repeated in urban areas across the country. Since the inception of the interstate system, transportation professionals have been striving to determine how best to operate and maintain that investment and tackle the challenge of congestion and growth. In 1969, Congress passed the National Environmental Policy Act (NHPA),7 which represented one of the first broad efforts by the government to establish a framework for protecting the environment. This law, which applied to all branches of the government, directed agencies to consider the environment before advancing any major federal action or project that would significantly impact the environment in the United States. It goes without saying that NEPA requirements had a direct impact on transportationrelated project such as airports, highways, and other transportation facilities. Among the most visible of impacts, federal agencies were required to conduct environmental assessments (EAs) and develop environmental impact statements (EISs) in advance of major projects.!~ These assessments are designed to identify the likelihood of environmental impacts of projects when compared to other courses of action. In addition to the NEPA act, Congress passed the 1970 Clean Air Act (CAA) and 1977 Oean Air Act Amendments (CAAA),8 which shifted the role of government in controlling air pollution. The intent of these acts was to protect public health and public welfare and to regulate emissions of hazardous air pollutants. They authorized

Introduction

FHllURE

1.6 Early traffic monitOring on Interstate 45 (1-45) Gulf Freeway, Houston, Texas.

(©rn.)

F11uRE

1.7 Early traffic monitoring technology, Interstate 45 (1-45) Gulf Freeway, Houston, Texas.

(© rn.)

7

8

Chapter One federal and state regulations to limit stationary and mobile source emissions and created four regulatory programs to oversee these regulations. They were the National Ambient Air Quality Standards (NAAQS), State Implementation Plans (SIPs), New Source Performance Standards (NPS), and National Emission Standards for Hazardous Air Pollutants (NESHAPs). The 1977 amendments included provisions for the Prevention of Significant Deterioration (PSD) of air quality in areas attaining the NAAQS and requirements for non-attainment areas. Non-attainment areas are those geographic regions not meeting the federal air quality standards. The 1990 CAAA9 amended the original CAA to set new goals (dates) for achieving attainment of NAAQS since many areas of the country were having difficulty meeting the deadlines. Key components of the amendments included the requirement of technology-based standards for major pollution sources and certain area pollution sources, and the establishment and periodic review of emission standards (i.e., maximum achievable control technology) that require the maximum degree of reduction in emissions of hazardous air pollutants. In addition to environmental legislation related to clean air, Congress focused on disabled citizens with the passage of the Americans with Disabilities Act (ADA)10 in 1990. This act, which was signed into law on July 26, 1990, by President George H. W. Bush, represented one of the country's most comprehensive pieces of civil rights legislation related to people with disabilities. The primary focus of the legislation was to ensure that citizens with disabilities have the same opportunities as everyone else to participate in all aspects of life, including employment opportunities, the purchase of goods and services, and to participate in state and local government programs and services. The ADA had broad transportation implications including the accommodation of disabilities in surface transportation services such as city buses, public rail transit, and sidewalks. 11 In 1991, Congress passed the Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA),u which continued to focus on authorization for highways, highway safety, and mass transit. Signed by President Bush, the bill authorized expenditures of $155 billion, established the National Highway System (NHS), and gave state and local governments more flexibility in determining transportation solutions for their jurisdictions. Additionally, the legislation highlighted new technologies as potential solutions to improving the efficiency and safety of the transportation network. Key components of the law allowed highway funds to be used for transportation-related environmental projects and emphasized highway safety by establishing a new program to encourage use of safety belts and motorcycle helmets. Other measures established uniformity in state vehicle registration and fuel tax reporting to streamline efforts and improve productivity. President Clinton signed the Transportation Equity Act for the 21st Century (TEA-21)13 in 1998, which built on the initiatives of !STEA. The legislation had four key thrust areas: rebuilding America, improving safety, protecting the environment, and creating opportunity. The guaranteed $198 billion investment included in the bill was intended to balance the federal investment across highways, transit, intermodal projects, and technologies while continuing to encourage state and local flexibility in expenditures. Safety programs highlighted the importance of improving safety belt use, fighting drunk driving, and improving truck safety programs across the country. Other efforts targeted increasing pipeline safety and that of rail-highway grade crossings. Protecting the public health and the environment included the expansion of Congestion Mitigation and Air Quality (CMAQ) improvement and transportation enhancements

Introduction programs, extension of programs for the construction of National Scenic Byways, pedestrian and bicycle paths, and recreational trails, as well as incentives to increase transit ridership. Finally, as with virtually every other transportation authorization bill, TEA-21 helped expand access to jobs and through innovative programs as well as continued the effective Disadvantaged Business Enterprise program. The Safe Accountable Flexible Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU)14 was a funding bill signed in 2005 by George W. Bush. This bill, which guaranteed $244.1 billion in funding for highways, highway safety, and public transportation, had the following focus areas: safety, equity, innovative finance, congestion relief, mobility and productivity, efficiency, environmental stewardship, and environmental streamlining. Unique aspects of the bill include the establishment of the highway safety improvement program (HSIP) and other programs targeting safe routes to school, work zone safety, bicycle and pedestrian safety, and the improvement of traffic control devices targeted to older drivers and pedestrians, toll facilities, and motorcycle safety. Congestion relief provisions gave states more options to use road pricing to manage congestion and enhanced and clarified the use and operations of highoccupancy vehicle (HOV) lanes to ensure degradation of operations does not occur. In 2012, President Obama signed the act entitled Moving Ahead for Progress in the 21st Century (MAP-21).15 This bill had as its key tenets to strengthen America's highways by expanding the NHS to incorporate arterials, to establish the National Highway Performance Program, and to establish a performance-based program for more efficient investment of federal transportation resources. The bill authorized $82 billion for road, bridge, bicycling, and walking improvements to help create jobs and support economic growth. It continued the HSIP by doubling funding for infrastructure safety projects to improve progress toward reducing highway fatalities and also focused on distracted driving, transit safety, and motor carrier safety. Furthermore, it emphasized the importance of improving timely delivery of projects and efficiency in the development process from planning to completion. The most recent authorization bill, signed by President Obama in 2015, was the Fixing America's Surface Transportation Act (FAST Act}. 16 This legislation authorized $305 billion for highway, highway and motor vehicle safety, public transportation, motor carrier safety, hazardous materials safety, rail, research, technology, and statistics programs. Included in its major provisions were programs to improve safety, maintain the condition of the transportation system, reduce congestion and improve efficiency and freight movement, protect the environment, and to further reduce delays in project delivery. All of the programs were intended to help create jobs, support economic growth, and improve mobility for all citizens. As evidenced by the progression of federal funding bills, the transportation industry has moved from the initial construction of the interstate system to the wholesale operation and maintenance of a system that is safer, more efficient, and sustainable. Today, the overall national policy agenda with respect to transportation focuses on maintaining and expanding the national transportation system and fostering a sound financial base for that system to create jobs and ensure its long-term reliability. Additional tenets focus on ensuring that the system supports public safety and national security, protects the environment and quality of life, is sustainable into the future, and looks to incorporating rapidly advancing technologies that can enhance the government's ability to provide a safe and efficient method of transporting people, goods, and services across the country. Transportation professionals inherit this system.

9

1.4 lhe Transportation Profession The transportation profession,. which originated within the discipline of civil engineering, has evolved to include a broad range of professionals aaoss a multitude of disciplines. Today, civil engineers make up only one segment of the transportation proression. These more traditional players in the transportation industry are now joined by professionals with expertise in such fields as economics, psychology, geography, public administration, city planning, political science, industrial engineering, electrical engineering, physics, mechanical engineering, mathematics, statistics, logistics, communications, archeology, geology, and environmental engineering. They all work together as a team to advance the improvement of transportation for all users. The critical challenges that these transportation professionals face on an ongoing basis include managing congestion, improving safety, providing equal access, and protecting the environment. They also strive to incorporate and adapt new technologies to enhance the system, work to secure financial resources for the transportation network, and develop institutional arrangements that foster collaboration and work toward a seamless network for the user. Sample focus areas include daily urban operations (Fig. 1.8), interchange design (Fig. 1.9), international border crossing inspections and

FH1u11111.8 Houston TranStar control room.(@ TxDOT.)

FllURE

1.9 Interchange design. (© rn.)

Introduction wait times (Fig. 1.10), bridge design (Fig. 1.11), pavement design (Fig. 1.12), and the impact of vehicle emissions on the environment (Fig. 1.13), in addition to a multitude of other topics all working to provide a safe and efficient transportation network for the traveling public.

F11uRE 1.10 U.S.-Mexlco border crossing.(© m.)

11

F11uRE 1.11 Bridge research and inspe11-18

c

>18--26

D

>26-35

E

>35--45

F

Demand exceeds capacity OR density> 45

TABLE

3.6.1

3.3 LOS Criteria for Basic Freeway Segments (Ref.1.)

LOS, Density, Speed, and Flow Rates

The HCM measures LOS to specific densities, as illustrated in Table 3.3 and for which the speed-flow curves are illustrated in Fig. 3.11. The speed flow curves are based on the equations presented in Table 3.4, illustrating the range of flows that exist for basic freeway segments for different speeds.

3.6.2

Computing LOS and Capacity for a Basic Freeway Segment

The steps for determining a facilitie's LOS or capacity for a signalized intersection basic freeway segment includes a series of computations that start with the FFS and refine that speed based on variations from the base conditions. A generalized process is illustrated in Fig. 3.12.

Step 1: Collect Input Data To analyze a basic freeway segment for capacity and LOS, various data elements are required that describe the geometric and demand characteristics of the segment. The required input data are provided in Table 3.5.

, I

I

60 milh

60

55 ml/h

I

I

,

,

,,

/

~ so +-~~~---1~ , :__~~~ '-+-~~,..:....~~~~~--+~-"""'.z:._----j

~

E

I

LOSA

/

/

LOSB/

/'

L

/

LOSE

,

: ; 40 +-~~~~'-+-~-+-' ~---1--.~~~'-+-~-,~,~' ~'-'-+-~~~----1 ~

8.

w

,'

,,

30 -t-~~'-r-~:'--.,_.7"---...--t-'"--i-"~~r-~~~-+-~~~----1

LOSF

500

1000

1500

Flow rate (pc/h/ln)

F1auRE 3 ..1.1

LOS for basic freeway segments. (Ref. 1.)

2000

2500

87

88

Ch a pt e r Th re e Flow Rate Range

FFS (ml/h)

Breakpoint

~reakpolnt

75

1000

75

75--0.00001107(V0

70

1200

70

65

1400

60 55 TABLE

3.4

Capacity

~reakpolntSCapac~y -

1000)2

2400

70-0.00001160(v0

-

1200)

2

2400

65

65-0.00001418(v

-

1400)2

2350

1600

60

60-0.00001816(v0

-

1600)

2

2300

1800

55

55-0.00002469 (V0

1800)

2250

0

-

2

Equations Describing Speed Flow Curves for LOS for Basic Freeway Segments (Ref.1.)

Step 2: Estimate and Adjust FFS Once the input data have been collected, the FFS can be calculated using the following formula: FFS = BFFS - fLw - fzr. - 3.22TRD"·e1 where FFS = free-flow speed BFFS =base FFS for the basic freeway segment (mph/h) fLw =adjustment factor for lane widths (mi/h) fLC =adjustment factor for lateral clearance (mi/h) TRD =total ramp density (ramps/mi)

Step 1: Colect Input data

Step 2: Es1inate and adjust FFS

Step 3: Estinate and adjust capacity

Step 4: Adjust demand volume

Step 5: Estimate speed and density

Step 6: Determine LOS FlGiURE 3.12

LOS and capacity computational steps for basic freeway segments. (Ref.1.)

T raff i c FI ow Th eo r 1 a nd Ca pa c it 1 Required Input Data

Data Elements

Freeway data

• Free-flow speed (FFS) • Number of mainline freeway lanes in one direction • Lane width • Right-side lateral clearance • Total ramp density • Terrain (i.e., level, rolling, mountainous, length and percent grade)

Demand data

• Demand during the analysis hour or daily demand • Presence of heavy vehicles • Peak hour factor (PFH) • Driver population factor

Length of analysis period

TABLE

3.5

• The analysis period for the freeway analysis; typically the peak 15-min period with the peak hour

Required Input Data for Basic Freeway Segments (Ref. l.)

If the average lane width in the basic segment is less than 12 ft, then the adjustment factor for the reduced lane width needs to be used. As noted previously, if the lanes are

narrower than typical, a driver may operate their vehicle in a more cautious manner to ensure they stay within the lane. The adjustment factors for average lane width are shown in Table 3.6. If the clearance on the right side of the basic freeway segment is less than the typical 6 ft, then the FFS needs to be adjusted according to the factors provided in Table 3.7. Note that the more lanes the segment has, the less impact the reduced right-side clearance has on the FFS. Total ramp density is a measure of the impact of merging and diverging vehicles on FFS. The practitioner can further adjust the FFS for a basic freeway segment to account for such conditions as work zones, weather, or local conditions. The formula for calculating this adjusted speed is the following: FFSadi = FFS x SAF where FFS•dJ =the adjusted free-flow speed FFS = free-flow speed SAF =the speed adjustment factor Typically, for basic freeway segments, the SAF is equal to 1. Average LMe Width (ft)

Reduction In FFS, f.,., (ml/h)

~12

0.0

~11-12

1.9

~10-11

6.6

TABLE

3.6 Adjustment to FFS for Average Lane Width, fl..W(Ref.1.)

89

90

Cha pt e r T hre e

Right-Side Lateral Clearance (ft)

>6 5

4

3 2 1 0 TABLE

3.7

Lanes In One Direction

2

3

4

0.0 0.6 1.2 1.8 2.4 3.0 3.6

0.0 0.4 0.8 1.2 1.6 2.0 2.4

0.0 0.2 0.4 0.6 0.8 1.0 1.2