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This work was sponsored by the American Association of State Highway and
Transportation Officials, in cooperation with the Federal Highway Administration, and
was conducted in the National Cooperative Highway Research Program, which is
administered by the Transportation Research Board of the National Research Council.

This is the final draft assubmitted by the research agency. The opinions and
conclusions expressed or implied in the report are those of the research agency. They are
not necessarily those of the Transportation Research Board, the National Research
Council, the Federal Highway Administration, the American Association of State
Highway and Transportation Officials, or the individual states participating in the
NationalCooperative Highway Research Program.

1.1.1 BACKGROUND Objective of the Design Guide
The overall objective of the Guide for the Mechanistic-Empirical Design of New and
Rehabilitated Pavement Structures (referred to hereinafter as the Design Guide) is to provide the
highway community with a state-of-the-practice tool forthe design of new and rehabilitated
pavement structures, based on mechanistic-empirical principles. This objective was
accomplished through developing the following:

The Design Guide itself, which is based on comprehensive pavement design procedures
that use existing mechanistic-empirical technologies.
User-oriented computational software and documentation based on the Design Guideprocedure.

The Design Guide represents a major change in the way pavement design is performed. The
designer first considers site conditions (traffic, climate, subgrade, existing pavement condition
for rehabilitation) and construction conditions in proposing a trial design for a new pavement or
rehabilitation. The trial design is then evaluated for adequacy through the prediction of keydistresses and smoothness. If the design does not meet desired performance criteria, it is revised
and the evaluation process repeated as necessary. Thus, the designer is fully involved in the
design process and has the flexibility to consider different design features and materials for the
prevailing site conditions. This approach makes it possible to optimize the design and to more
fully insurethat specific distress types will not develop.
The mechanistic-empirical (M-E) format of the Design Guide provides a framework for future
continuous improvement to keep up with changes in trucking, materials, construction, design
concepts, computers, and so on. In addition, guidelines for implementation and staff training
have been prepared to facilitate use of the new design procedure, aswell as strategies to
maximize acceptance by the transportation community. Economic Justification for a Revised and Improved Design Guide
The nation’s highways reached an estimated 2.7 trillion vehicle-miles in 2000. This is four times
the 1960 level. This amounts to 7.4 billion vehicle-miles of travel every day. Truck travel
(single-unit and combinations) has increased 231 percent since1970. Combination truck travel
has increased 285 percent over 1970 levels and now accounts for 4.9 percent of total annual
vehicle-miles of travel versus 3.2% in 1970. (1) The 4 million miles of U.S. roadways (with 2
million miles of paved roads) have been constructed, rehabilitated, and maintained over the
previous century, and they represent a huge national investment that has provided asafe and


comfortable means of transportation for both private and commercial vehicles. Highways have
contributed significantly to the economic growth of the nation.
Pavement structures wear down and deteriorate under heavy axle loadings and exposure to the
elements (very hot and very cold temperatures, freezing and thawing, precipitation). Therefore,
they must be maintained and...
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