Traffic and highway engineering

Tai Lieu Chat Luong


Traffic and
Highway
Engineering
FOURTH EDITION

Nicholas J. Garber
Lester A. Hoel
University of Virginia

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Traffic and Highway Engineering, Fourth Edition
Nicholas J. Garber and Lester A. Hoel
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This book is dedicated to our wives,
Ada and Unni
and to our daughters,
Allison, Elaine, and Valerie
and
Julie, Lisa, and Sonja
With appreciation for the support, help, and encouragement that we received
during the years that were devoted to writing this textbook.


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Contents
P A R T 1 䊏 INTRODUCTION
1

The Profession of Transportation
Importance of Transportation
Transportation History

6
Transportation Employment
Summary
23
Problems
24
References
25

2

1
3
3
16

Transportation Systems and Organizations
Developing a Transportation System
Modes of Transportation
34
Transportation Organizations
47
Summary
51
Problems
52
References
54

27

P A R T 2 䊏 TRAFFIC OPERATIONS
3

27

55

Characteristics of the Driver, the Pedestrian,
the Vehicle, and the Road
57
Driver Characteristics
58
Perception-Reaction Process
60
Older Drivers’ Characteristics
61
Pedestrian Characteristics
62
Bicyclists and Bicycles Characteristics
Vehicle Characteristics
63
Road Characteristics
88

62

v

vi

Contents
Summary
Problems
References

4

93
95
98

Traffic Engineering Studies
Spot Speed Studies
100
Volume Studies
115
Travel Time and Delay Studies
Parking Studies
139
Summary
146
Problems
147
References
150

5

Highway Safety

99
133

151

Issues Involved in Transportation Safety
Strategic Highway Safety Plans
154
Effectiveness of Safety Design Features
Summary
208
Problems
208
References
212

6

152
190

Fundamental Principles of Traffic Flow

213

Traffic Flow Elements
213
Flow-Density Relationships

218
Shock Waves in Traffic Streams
230
Gap and Gap Acceptance
243
Introduction to Queuing Theory
249
Summary
258
Problems
258

7

Intersection Design

265

Types of At-Grade Intersections
266
Design Principles for At-Grade Intersections
Design of Railroad Grade Crossings
314
Summary
320
Problems
322
References
325

8

Intersection Control

276

327

General Concepts of Traffic Control
327
Conflict Points at Intersections
331
Types of Intersection Control
332
Signal Timing for Different Color Indications
Freeway Ramps
373
Summary
378
Problems
378
References
380

342


Contents

9

Capacity and Level of Service for Highway Segments
Two-Lane Highways
Freeways
406
Multilane Highways
Summary
430
Problems
431
References
434
Appendix: Tables

10

382
424

434

Capacity and Level of Service at Signalized Intersections
Definitions of Some Common Terms
457
Level of Service at Signalized Intersections
Summary
528
Problems
528
References

533
Appendix: Tables
534

460

PART 3 䊏 TRANSPORTATION PLANNING
11

381

The Transportation Planning Process

549
551

Basic Elements of Transportation Planning
Transportation Planning Institutions
562
Urban Transportation Planning
566
Forecasting Travel
574
Summary
586
Problems
587
References
588

12 Forecasting Travel Demand

552

591

Demand Forecasting Approaches
591
Trip Generation
593
Trip Distribution
603
Mode Choice
613
Traffic Assignment
625
Other Methods for Forecasting Demand
Estimating Freight Demand
637
Traffic Impact Studies
638
Summary
644
Problems
645
References
652

13 Evaluating Transportation Alternatives
Basic Issues in Evaluation

653
Evaluation Based on Economic Criteria
Evaluation Based on Multiple Criteria
Summary
684
Problems
684
References
689

633

653
657
669

457

vii


viii

Contents

P A R T 4 䊏 LOCATION, GEOMETRICS,
AND DRAINAGE
14 Highway Surveys and Location

691

693

Principles of Highway Location
693
Highway Survey Methods
701
Highway Earthwork and Final Plans
723
Summary
731
Problems
733
References
734

15 Geometric Design of Highway Facilities

737

Factors Influencing Highway Design
738
Design of the Alignment
754
Special Facilities for Heavy Vehicles on Steep Grades
Bicycle Facilities
791
Parking Facilities
796
Computer Use in Geometric Design
801

Summary
802
Problems
802
References
805

16 Highway Drainage

790

807

Surface Drainage
807
Highway Drainage Structures
809
Sediment and Erosion Control
811
Hydrologic Considerations
813
Unit Hydrographs
826
Hydraulic Design of Highway Drainage Structures
Subsurface Drainage
870
Economic Analysis
889
Summary
889

Problems
889
References
891
Additional Readings
892

P A R T 5 䊏 MATERIALS AND PAVEMENTS
17 Soil Engineering for Highway Design
Soil Characteristics
895
Basic Engineering Properties of Soils
Classification of Soils for Highway Use
Soil Surveys for Highway Construction
Soil Compaction
922
Special Soil Tests for Pavement Design
Frost Action in Soils
936
Summary
937
Problems
937
References
914

827

893
895

899
907
917
932


Contents

18 Bituminous Materials

943

Sources of Asphalt
943
Description and Uses of Bituminous Binders
Properties of Asphalt Materials
949
Tests for Asphalt Materials
953
Asphalt Mixtures
969
Superpave Systems
992
Summary
1019
Problems
1019
References
1022

19 Design of Flexible Pavements

1025

Structural Components of a Flexible Pavement
Soil Stabilization
1027
General Principles of Flexible Pavement Design
Summary
1070
Problems
1070
References
1073

20 Design of Rigid Pavements

946

1025
1032

1075

Materials Used in Rigid Pavements
1076
Joints in Concrete Pavements
1081
Types of Rigid Highway Pavements

1083
Pumping of Rigid Pavements
1084
Stresses in Rigid Pavements
1085
Thickness Design of Rigid Pavements
1093
Summary
1129
Problems
1129
References
1131

21

Pavement Management

1133

Problems of Highway Rehabilitation
1133
Methods for Determining Roadway Condition
Pavement Condition Prediction
1151
Pavement Rehabilitation
1160
Pavement Rehabilitation Programming
1162
GIS and Pavement Management

1172
Summary
1174
Problems
1174
References
1176

Appendixes
Index

1207

1177

1136

ix


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Preface
Traffic and Highway Engineering, Fourth Edition, is designed for students in engineering programs where courses in transportation, highway, or traffic engineering are
offered. In most cases, these courses are taught in the third or fourth year but are also
covered at the graduate level. This book also is designed to serve as a professional
reference. Thus, the objectives of this textbook are: (1) To be a contemporary and
complete text in highway and traffic engineering that can be used primarily at the
undergraduate level. It may be used at the graduate level for courses that emphasize

highway topics. Due to its complete coverage of the material, the textbook is designed
for flexible use in developing a single course or for use in two or more courses. (2) To
serve as a reference for engineers in the highway field and as a study guide for use in
preparing for the professional engineering license exam, review courses, and preparation for graduate comprehensive exams in transportation engineering.
Since the subject of transportation engineering is a broad one, several approaches
can be used to introduce this topic to students. One approach is to cover all transportation modes—air, highway, pipeline, public, rail, and water—in an overview-type
course. This approach ensures comprehensive coverage but tends to be superficial
with uneven coverage of some modes and can be lacking in depth. A second approach
is to present the subject of transportation by generic elements, such as vehicle and
guideway characteristics, capacity analysis, planning, design, safety, human factors,
administration, finance, system models, information technology, operations, and so
forth. This approach is appealing because each of the modes is considered within a
common context and the similarities between various modes are emphasized. Our
recent textbook, Transportation Infrastructure Engineering: A Multi-Modal Integration, is based on this concept. A third approach is to emphasize one mode, such as
highways, airports, maritime, transit, or railroads, where the material is specific and
unambiguous and the subject matter can be directly applied in practice. There is considerable pedagogical merit in focusing on one mode, which is followed herein.
xi


xii

Preface

This book emphasizes the subject of traffic and highway engineering, which is a
major area within civil engineering. It appeals to students because they can relate
directly to problems created by motor vehicle travel. We believe that this topic is
appropriate within a transportation curriculum or as an introductory transportation
course because it provides an opportunity to present material that is not only useful
to engineering students who may pursue careers in or related to transportation engineering, but is also interesting and challenging to those who intend to work in other
areas. Furthermore, this book can serve as a reference for practicing transportation

engineers and for use by students in graduate courses. Thus, our overall objective is to
provide a way for students to get into the area of transportation engineering, develop
a feel for what it is about, and thereby experience the challenges of the profession.
The text chapters present materials that will help students understand the basis
for transportation, its importance, and the extent to which transportation pervades
our daily lives. The text also provides information about the basic areas in which
transportation engineers work: traffic operations and management, planning, design,
construction, and maintenance. Thus, this book has been categorized into five parts:
Part 1, Introduction (to the profession, its history, systems, and organizations) Part 2,
Traffic Operations; Part 3, Transportation Planning; Part 4, Location, Geometrics,
and Drainage; and Part 5, Materials and Pavements.
The topical division of the book organizes the material so that it may be used in
one or more separate courses. For a single course in transportation engineering,
which is usually offered in the third year where the emphasis is on traffic and highway
aspects, we recommend that material from Parts 1, 2, and 3 (Chapters 1–13) be covered. For a course in highway engineering, where the emphasis is on highway location,
design, materials, and pavements, we recommend that material from Parts 2, 4, and 5
(Chapters 3 and 14–21) be used. A single introductory course in transportation facilities design could include Chapters 1, 2, 3, 14, 15, 16, 19, and 21.
The book also is appropriate for use in a two-semester sequence in transportation
engineering in which traffic engineering and planning (Chapters 3–13) would be covered in the first course, and highway design (Chapters 14–21) would be covered in the
second course.
The success of our textbook has been a source of great satisfaction, because we
believe that it has contributed to the better understanding of highway transportation
in all its dimensions. We wish to thank our colleagues and their students for selecting
this book for use in transportation courses taught in colleges and universities
throughout the United States. The fourth edition builds on this experience and the
success of our pedagogic approach, which is to include many examples in each chapter
that illustrate basic concepts, a list of references, a comprehensive problem set at
the end of each chapter (with complete instructor’s manual), an organizational structure that subdivides the material into logical and easy-to-understand elements, and a
large number of tables and diagrams that augment the text and ensure completeness
of material.

Transportation is a fast-moving field, and the fourth edition reflects many
changes that have occurred since the book was first published in 1988 and the
third edition published in 2002. In the fourth edition, we have added new material
and expanded and updated each chapter to reflect new methods, procedures, and


Preface

xiii

technology. The number and variety of homework problems have been increased and
section numbering has been added.
The authors are indebted to many individuals who assisted in reviewing various
chapters and drafts of the original manuscript. We especially wish to thank the
following for their helpful comments and suggestions: Edward Beimborn, David
Boyce, Christian Davis, Michael Demetsky, Richard Gunther, Jerome Hall, Jotin
Khisty, Lydia Kostyniak, Michael Kyte, Winston Lung, Kenneth McGhee, Carl Monismith, Ken O’Connell, Anthony Saka, Robert Smith, Egons Tons, Joseph Wattleworth, Hugh Woo, and Robert Wortman.
In the preparation of later editions, we are indebted to many colleagues who provided helpful comments and suggestions. We also thank several of our colleagues and
students who read specific chapters and suggested new end-of-chapter problems.
Those whom we particularly wish to acknowledge are Maher Alghazzawi, Rakim
Benekohal, Stephen Brich, Bernard Carlson, Stacey Diefenderfer, Brian Diefenderfer, Conrad Dudek, Lily Elefteriadou, Thomas Freeman, Ron Gallagher, Alan Gesford, Arkopal Goswami, Jiwan Gupta, Kathleen Hancock, Marvin Hilton, Feng-Bor
Lin, Qun Liu, Yuan Lu, Catherine McGhee, Richard McGinnis, John Miller, Jack
Page, Brian Park, Adel Sadek, Mitsuru Saito, Gerald Seeley, Ed Sullivan, James
Taylor, Joseph Vidunas, Peter Weiss, W. James Wilde, F. Andrew Wolfe, Shaw Yu,
and Yihua Ziong.
We thank Richard Boaz and Michael Zmuda and the Virginia Department of
Transportation’s Survey & Photogrammetry Section within Location & Design and
the Virginia Transportation Research Council for their help and support. We also
thank Lewis Woodson and Chase Buchannan for responding to our call for new photographs. The many organizations cited herein that permitted us to include material
from their publication deserve special mention because, without their support, our

book would not have been a reality.
And finally, we wish to thank the reviewers of the fourth edition for their
insightful comments and helpful suggestions: Per Garder, Tom Maze, Thomas Nelson,
Emelinda Parentela, Hamid Soleymani, James Stoner, Rod Turochy, and Erol Tutumluer, and to our editors, Jane Carlson and Hilda Gowans, for their help and guidance
in the preparation of this edition.
Nicholas J. Garber
Lester A. Hoel


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About the Authors

Nicholas J. Garber is the Henry L. Kinnier Professor of Civil Engineering at the
University of Virginia and served as chairman of the Department from 1996 to 2002.
Before joining the University of Virginia, Dr. Garber was Professor of Civil Engineering in the faculty of Engineering of the University of Sierra Leone, where he was
also the Dean of the faculty of Engineering. He taught at the State University of New
York at Buffalo, where he played an important role in the development of the graduate program in Transportation Engineering. Dr. Garber worked as a Design Engineer for consulting engineering firms in London between 1961 and 1964 and as
an Area Engineer and Assistant Resident Engineer in Sierra Leone between 1964
and 1967.
Dr. Garber received the degree of Bachelor of Science (B.S.) in Civil Engineering
from the University of London and the Masters (M.S.) and Doctoral (Ph.D.) degrees
from Carnegie-Mellon University.
Dr. Garber’s research is in the areas of Traffic Operations and Highway Safety. He
has been the principal investigator for many federal-, state-, and private-agencysponsored research projects. He is the author of over 120 refereed publications and
reports. He is a co-author of the textbook Transportation Infrastructure Engineering:
A Multi-Modal Integration, Thomson/Nelson, 2007.
Dr. Garber is a member of the Executive Committee of the Transportation Research
Board (TRB) and served for many years as chair of the TRB Committee on Traffic

Safety in Maintenance and Construction Operations, currently the Committee on
Work Zone Traffic Control. He has served as a member of several TRB Policy Studies
xv


xvi

About the Authors

on speed management, size and weight of large trucks, transportation of hazardous
materials, and research priorities and coordination in highway infrastructure and
operations safety. He is also a member of the TRB Oversight Committee for the
Strategic Highway Research Program II (SHRP II). Dr. Garber also has served as a
member of several other national committees of the American Society of Civil Engineers (ASCE) and The Institute of Transportation Engineers (ITE). He is a member
of the Editorial Board of the ASCE Journal of Transportation Engineering.
Dr. Garber is a member of the National Academy of Engineering. He is a recipient of
many awards, including the TRB D. Grant Mickle Award, the ITE Edmund R. Ricker
Transportation Safety Award, and the American Roads and Transportation Builders
(ARTBA) S. S. Steinberg Outstanding Educator Award. He is listed in Who’s Who in
Science and Engineering and Who’s Who in the world.
Dr. Garber is a Fellow of the American Society of Civil Engineers, a Fellow of the
Institute of Transportation Engineers, a Fellow of the Institution of Civil Engineers
of the United Kingdom, a member of the American Society for Engineering Education, and a member of Chi Epsilon.

Lester A. Hoel is the L. A. Lacy Distinguished Professor of Engineering and the
Director of the Center for Transportation Studies at the University of Virginia. He
held the Hamilton Professorship in Civil Engineering from 1974 to 1999. From 1974
to 1989 he was Chairman of the Department of Civil Engineering. Previously, he was
Professor of Civil Engineering and Associate Director, Transportation Research
Institute at Carnegie-Mellon University. He has been a registered professional engineer in California, Pennsylvania, and Virginia. His degrees are: BCE from the City

College of New York, MCE from the Polytechnic Institute of New York, and the
Doctorate in Engineering from the University of California at Berkeley.
Dr. Hoel’s area of expertise is the management, planning, and design of surface transportation infrastructure with emphasis on highway and transit systems. He is an
author of over 150 publications and was co-editor (with G.E. Gray) of the textbook
Public Transportation, and co-author (with N.J. Garber and A.W. Sadek) of the textbook Transportation Infrastructure Engineering: A Multi-Modal Integration.
Dr. Hoel is a member of the National Academy of Engineering, a Fellow of the American Society of Civil Engineers, a Fellow of the Institute of Transportation Engineers,
a member of the American Society for Engineering Education and the Norwegian
Academy of Technical Sciences. As a student, he was elected to the national honor
societies Chi Epsilon, Tau Beta Pi, and Sigma Xi. He was a member of the Executive
Committee of the Transportation Research Board (TRB) from 1981 to 1989 and from
1995 to 2004 and served as its Chairman in 1986. He was an ex-officio member of the
National Research Council (NRC) Governing Board of the National Academies and
the Transportation Research Board Division Chairman for NRC Oversight from 1995
to 2004. In that capacity, he was responsible for oversight of the NRC review process


About the Authors

xvii

for all TRB policy studies produced during that period. He served as the Chairman of
two congressionally mandated policy studies. He also has served on TRB technical
committees and NCHRP/ TCRP panels. He is a member of the TRB Transit Research
Analysis Committee, whose purpose is to advise the Federal Transit Administration
on its research program, and is a member of the National Research Council Report
Review Committee, in which he oversees the review process for policy studies prepared by the National Research Council of the National Academies.
He is a recipient of the American Society of Civil Engineers’ Huber Research Prize,
the Transportation Research Board Pyke Johnson Award, the Highway Users Federation Stanley Gustafson Leadership Award, the TRB W.N. Carey, Jr. Distinguished
Service Award, the ASCE Frank Masters Transportation Engineering Award, the
ASCE James Laurie Prize, the Virginia Society of Professional Engineers Service

Award, the Institute of Transportation Engineers’ Wilbur Smith Distinguished
Educator Award, the American Road and Transportation Builders S. S. Steinberg
Outstanding Educator Award, and the Council of University Transportation Centers
Distinguished Professor Award. He is listed in Who’s Who in America.
Dr. Hoel has served as president of the Council of University Transportation Centers
and on the ASCE accreditation board for engineering and technology. He was
chairman of the Board of Regents of the Eno Transportation Foundation Leadership
Center and served on its Board of Advisors. He also has served on the editorial boards
of transportation journals, including Transportation Research, Journal of Advanced
Transportation, Journal of Socio-Economic Planning Sciences, Journal of Specialized
Transportation, Computer-Aided Civil and Infrastructure Engineering, and Urban
Resources.


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P A R T

1

Introduction

T

ransportation is essential for a nation’s development and growth. In both the
public and private sector, opportunities for engineering careers in transportation
are exciting and rewarding. Elements are constantly being added to the world’s
highway, rail, airport, and mass transit systems, and new techniques are being applied
for operating and maintaining the systems safely and economically. Many organizations and agencies exist to plan, design, build, operate, and maintain the nation’s transportation system.

CHAPTER 1

CHAPTER 2

The Profession of Transportation
Importance of Transportation
Transportation History
Transportation Employment
Summary
Problems
References

Transportation Systems and Organizations
Developing a Transportation System
Modes of Transportation
Transportation Organizations
Summary
Problems
References

1


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CHAPTER 1

The Profession

of Transportation

F

or as long as the human race has existed, transportation has played a significant
role by facilitating trade, commerce, conquest, and social interaction, while
consuming a considerable portion of time and resources. The primary need
for transportation has been economic, involving personal travel in search of food or
work, travel for the exchange of goods and commodities, exploration, personal
fulfillment, and the improvement of a society or a nation. The movements of people
and goods, which is the basis of transportation, always has been undertaken to accomplish those basic objectives or tasks that require transfer from one location to another.
For example, a farmer must transport produce to market, a doctor must see a patient
in the office or in the hospital, and a salesman must visit clients located throughout a
territory. Every day, millions of people leave their homes and travel to a workplace—
be it a factory, office, classroom, or distant city.

1.1 IMPORTANCE OF TRANSPORTATION
Tapping natural resources and markets and maintaining a competitive edge over other
regions and nations are linked closely to the quality of the transportation system. The
speed, cost, and capacity of available transportation have a significant impact on the
economic vitality of an area and the ability to make maximum use of its natural
resources. Examination of most developed and industrialized societies indicates that
they have been noted for high-quality transportation systems and services. Nations
with well-developed maritime systems (such as the British Empire in the 1900s) once
ruled vast colonies located around the globe. In more modern times, countries with
advanced transportation systems—such as in the United States, Canada, Asia, and
Europe—are leaders in industry and commerce. Without the ability to transport manufactured goods and raw materials and without technical know-how, a country is
3

4

Part 1

Introduction

unable to maximize the comparative advantage it may have in the form of natural
or human resources. Countries that lack an abundance of natural resources rely
heavily on transportation in order to import raw materials and export manufactured
products.

1.1.1 Transportation and Economic Growth
Good transportation, in and of itself, will not assure success in the marketplace, as the
availability of transportation is a necessary but insufficient condition for economic
growth. However, the absence of supportive transportation services will serve to
limit or hinder the potential for a nation or region to achieve its economic potential.
Thus, if a society expects to develop and grow, it must have a strong internal transportation system consisting of good roads, rail systems, as well as excellent linkages to
the rest of the world by sea and air. Thus, transportation demand is a byproduct
derived from the needs and desires of people to travel or to transfer their goods from
one place to another. It is a necessary condition for human interaction and economic
competitiveness.
The availability of transportation facilities can strongly influence the growth and
development of a region or nation. Good transportation permits the specialization of
industry or commerce, reduces costs for raw materials or manufactured goods, and
increases competition between regions, thus resulting in reduced prices and greater
choices for the consumer. Transportation is also a necessary element of government
services, such as delivering mail, defense, and assisting territories. Throughout history, transportation systems (such as those that existed in the Roman Empire and
those that now exist in the United States) were developed and built to ensure economic development and efficient mobilization in the event of national emergencies.

1.1.2 Social Costs and Benefits of Transportation

The improvement of a region’s economic position by virtue of improved transportation does not come without costs. Building vast transportation systems requires enormous resources of energy, material, and land. In major cities, transportation can
consume as much as half of all the land area. An aerial view of any major metropolis
will reveal vast acreage used for railroad terminals, airports, parking lots, and freeways. Transportation has other negative effects as well. Travel is not without danger;
every mode of transportation brings to mind some major disaster—be it the sinking of
the Titanic, the explosion of the zeppelin Hindenburg, the infrequent but dramatic
passenger air crashes, and highway accidents that each year claim about 40,000 lives
in the United States. In addition, transportation can create noise, spoil the natural
beauty of an area, change the environment, pollute air and water, and consume energy
resources.
Society has indicated a willingness to accept some risk and changes to the natural
environment in order to gain the advantages that result from constructing new transportation systems. Society also values many social benefits brought about by good
transportation. Providing medical and other services to rural areas and enabling


Chapter 1

The Profession of Transportation

5

people to socialize who live some distance apart are just a few examples of the benefits
that transportation provides.
A major task for the modern transportation engineer is to balance society’s need
for fast and efficient transportation with the costs involved. Thus, the most efficient
and cost-effective system is created, while assuring that the environment is not compromised or destroyed. In carrying out this task, the transportation engineer must
work closely with the public and elected officials and needs to be aware of modern
engineering practices to ensure that the highest quality transportation systems are
built consistent with available funds and accepted social policy.

1.1.3 Transportation in the United States

Is transportation very important? Why should you study the subject and perhaps consider transportation as a professional career? Many “gee whiz” statistics can be cited
to convince the reader that transportation is vital to a nation, but before doing so, consider how transportation impacts people’s daily lives.
Perusal of a local or national newspaper will inevitably produce one or more articles on transportation. The story might involve a traffic fatality, road construction
project, the price of gasoline, trends in purchases of motor vehicles, traffic enforcement and road conditions, new laws (such as cell phone use while driving), motor
vehicle license requirements, neighborhood protests regarding road widening or
extensions, proposals to increase road user fees or gasoline taxes to pay for maintenance and construction projects, the need for public transit services, or the debate
over “sprawl” versus “smart growth.” The enormity of transportation can be demonstrated by calculating the amount of land consumed for transportation facilities, such
as sidewalks, parking lots, roads, driveways, shoulders, and bike paths, which in some
cases can exceed 50 percent of the land area.
The examples cited suggest that transportation issues are largely perceived at
local and state levels where people live. Mayors and governors are elected based on
their promises to improve transportation without (of course) raising taxes! At the
national level, transportation does not reach the “top 10” concerns, and transportation is rarely mentioned in a presidential address or national debate. At this level,
issues of defense, health care, immigration, voting rights, taxes, and international relations take center stage. While most Americans probably know the name of the Secretary of State or Defense, few could answer the question, “Who is the Secretary of
Transportation?”
The Transportation Research Board of the National Academies periodically publishes a list of “critical issues” in transportation which are posted on their Web site.
Among the issues identified are: (1) congestion, (2) emergencies such as terrorism
and natural disasters, (3) energy and the environment, (4) older drivers, (5) vehicle
safety and driver behavior, and (6) relationships between national, state, and local
governmental institutions. Each issue suggests the importance of transportation and
the priorities of concern to the transportation professional community.
The importance of transportation in the United States also can be illustrated by
citing statistics that demonstrate its national and worldwide influence. Extensive data


6

Part 1

Introduction

are furnished by the Bureau of Transportation Statistics of the U.S. Department of
Transportation and posted on their Web site.
• Approximately 18 percent of U.S. household expenditure is related to transportation.
• Transportation accounts for about 28 percent of total energy consumption.
• Almost 100 percent of the energy utilized for propelling transport vehicles is
derived from petroleum resources.
• Over 50 percent of all petroleum products consumed in the United States are for
transportation purposes.
• Over 80 percent of eligible drivers are licensed to operate a motor vehicle.
• Each person in the Unites States travels an average of 12,000 miles each year.
• Over 10 percent of the work force is employed in a transportation-related
activity.
• There are almost four million miles of paved roadway, of which 754,000 miles are
used for intercity travel and 46,800 miles are interstate highways.
• There are approximately 140,300 miles of freight railroads, 5300 public use airports, 26,000 miles of navigable channels, and 359,000 miles of oil and gas
pipelines.
The Bureau of Transportation Statistics has also provided direct evidence of the
economic importance of transportation services with the following key findings as
quoted from its Web site:
• Transportation services contributed about $313 billion (or 5 percent) of the value
generated by the U.S. economy in 1992. This is roughly comparable to the value
added by the wholesale/retail trade industry or the health industry and more than
the individual shares of the agriculture, mining, and computer industries.
• Trucking accounts for 65 percent of the total value added by transportation services. The biggest contributors are in-house trucking, accounting for 38 percent,
and for-hire trucking, accounting for 27 percent. The next largest contributors are
air transportation and railroads, accounting for 13 percent and 11 percent of the
total value added of transportation services, respectively.
• Transportation will continue to play a key role in the economy—even as it shifts
from manufacturing to a focus on services. The provision of services is the largest

and fastest growing sector in the U.S. economy.

1.2 TRANSPORTATION HISTORY
The story of transportation in the United States has been the subject of many books
that have covered a 300-year period and include the development of many separate
modes of transportation. Among the principal topics are travel by foot and horseback,
automobile and truck travel, development of roads and highways, the building of
canals and inland waterways, expansion of the West, construction of railroads, the use
of public transportation (such as bus and metro systems in cities), and the development of air transportation.