Principles of Highway Engineering and Traffic Analysis

Principles of Highway Engineering and Traffic Analysis

Highways have played a key role in the development and sustainability of human
civilization from ancient times to the present. Today, in the U.S. and throughout the
world, highways continue to dominate the transportation system — providing critical
access for the acquisition of natural resources, industrial production, retail marketing
and population mobility. The influence of highway transportation on the economic,
social and political fabric of nations is far-reaching and, as a consequence, highways
have been studied for decades as a cultural, political, and economic phenomenon.
While industrial needs and economic forces have clearly played an important part in
shaping highway networks, societies’ fundamental desire for access to activities and
affordable land has generated significant highway demand, which has helped define
and shape highway networks.

In the twenty-first century, the role of highways in the transportation system
continues to evolve. In most nations, the enormous investment in highwaytransportation
infrastructure that occurred in the middle of the last century, which
included the construction of the U.S. interstate highway system (the largest
infrastructure project in human history), has now given way to infrastructure
maintenance and rehabilitation, improvements in operational efficiency, various
traffic-congestion relief measures, energy conservation, improved safety and
environmental mitigation. This shift has forced a new emphasis in highway
engineering and traffic analysis — one that requires a new skill set and a deeper
understanding of the impact of highway decisions.

Highway engineering and traffic analysis involve an extremely complex interaction
of economic, behavioral, social, political, environmental, and technological factors.
This complexity makes highway engineering and traffic analysis far more
challenging than typical engineering disciplines that tend to have an overriding focus
on only the technical aspects of the problem. To be sure, the technical challenges
encountered in highway engineering and traffic analysis easily rival the most
complex technical problems encountered in any other engineering discipline.
However, it is the economic, behavioral, social, political, and environmental elements
that introduce a level of complexity unequalled by any other engineering discipline.
The remaining chapters in this book do not intend to provide a comprehensive
assessment of the many factors that influence highway engineering and traffic
analysis. Instead, Chapters 2 through 8 seek to provide readers with the fundamental
elements and methodological approaches that are used to design and maintain
highways and assess their operating performance. This material constitutes the
fundamental principles of highway engineering and traffic analysis that are needed to
begin to grasp the many complex elements and considerations that come into play

during the construction, maintenance, and operation of highways.

The performance of road vehicles forms the basis for highway design guidelines and
traffic analysis. For example, in highway design, the determination of the length of
freeway acceleration and deceleration lanes, maximum highway grades, stopping
sight distances, passing sight distances, and numerous accident-prevention devices all
rely on a basic understanding of vehicle performance. Similarly, vehicle performance
is a major consideration in the selection and design of traffic control devices, the
determination of speed limits, and the timing and control of traffic signal systems.
Studying vehicle performance serves two important functions. First, it provides
insight into highway design and traffic operations and the compromises that are
necessary to accommodate the wide variety of vehicles (from high-powered sports
cars to heavily laden trucks) that use highways. Second, it forms a basis from which
the impact of advancing vehicle technologies on existing highway design guidelines
can be assessed. This second function is particularly important in light of the ongoing
unprecedented advances in vehicle technology. Such advances will necessitate more
frequent updating of highway design guidelines as well as engineers who have a
better understanding of the fundamental principles underlying vehicle performance.
The objective of this chapter is to introduce the basic principles of road vehicle
performance. Primary attention will be given to the straight-line performance of
vehicles (acceleration, deceleration, top speed, and the ability to ascend grades).
Cornering performance of vehicles is overviewed in Chapter 3, but detailed
presentations of this material are better suited to more specialized sources [Campbell
1978; Brewer and Rice 1983; Wong 2008].


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