Reaping the Benefits of the LTPP Investment
The billions of dollars that our Nation invests in highway infrastructure
each year has given us one of the best transportation systems in the
world. But how can we maximize that investment? And how can we improve
the performance of pavements so that they last longer? To answer these
questions, the highway community initiated the Long-Term Pavement
Performance (LTPP) program more than a decade ago.
Planned as a 20-year investigation of in-service pavements, the LTPP
program's goal was to provide the data, information, and products
needed to extend pavement life. Since the start of the LTPP pavement
monitoring in 1989, data have been collected for nearly 2,300 LTPP
test sections in the United States and Canada. This data has been
used to develop a range of products and procedures that are helping
States meet their need for longer lasting roads and maximize their
highway investment.
The software tool LTPPBind and the temperature prediction equations
upon which it is based, for example, allow engineers to more accurately
select the correct Superpave asphalt binder for their specific environmental
conditions. The improved reliability of the LTPPBind equations is
significant because it reduces the need for modified binders, which
can drive up construction costs. A national comparison of the asphalt
binders selected using LTPPBind and those selected using the original
Superpave system showed an annual construction cost savings of $50
million for the highway agencies using LTPPBind.
States have also benefitted from falling weight deflectometer (FWD)
calibration procedures developed by the LTPP program. FWDs are used
to evaluate the structural condition of a pavement, making accurate
FWD data critical to States that use that data to make decisions about
performing pavement rehabilitation. The LTPP FWD calibration procedures
and the four FWD calibration centers established in cooperation with
the State highway agencies in Minnesota, Nevada, Pennsylvania, and
Texas, help to ensure that the FWD data collected by States and the
LTPP program are as accurate as possible.
"FWD data plays a key role in developing our rehabilitation
strategy, the design of our rehabilitation, and the resulting life-cycle
cost analyses," says Gary Hoffman, Chief Engineer of the Pennsylvania
Department of Transportation (DOT). "Pennsylvania's FWD calibration
center has proved to be an excellent investment. With how much we
spend each year on rehabilitating our roads, we really need the most
accurate data we can get. Having the calibration center assures us
of that."
Another cost-cutting tool developed by LTPP researchers is the Rigid
Pavement Design software. The software helps highway engineers implement
improved guidelines for the design of portland cement concrete pavements
that were developed in 1998 by the National Cooperative Highway Research
Program (NCHRP). Using the software, an engineer can tailor the rigid
pavement design to site-specific conditions, materials, and traffic
situations, resulting in a design that is more cost-effective and
reliable. It is estimated that using the new guidelines reduces the
life-cycle costs of pavements by 30 percent compared to current procedures.
This means a potential savings of $52 million a year for U.S. highway
agencies.
The LTPP research also promises to yield future benefits. For example,
LTPP data has been used in the development of the 2002 Guide for
the Design of New and Rehabilitated Pavement Structures. This
publication, if adopted by the American Association of State Highway
and Transportation Officials (AASHTO), is intended to replace the
1993 AASHTO Guide for the Design of Pavement Structures, which
is recognized as being no longer adequate to meet the design challenges
faced by today's highway agencies. LTPP data is helping to address
some of the limitations of the current design guide. "The LTPP
database is providing a wealth of data that is being translated into
useable knowledge," says Matt Witczak of Arizona State University.
For example, the LTPP database contains performance data on rehabilitated
pavements and covers all climatic conditions in the United States,
while the American Association of State Highway Officials (AASHO)
road test, on which the current guide is based, was conducted at only
one location and did not consider rehabilitated pavements. The LTPP
test sections also cover a wide range of subgrade materials, in contrast
to the one type of subgrade used for all the pavement sections in
the AASHO road test.
Through products such as LTPPBind, the FWD calibration procedures,
and the 2002 Design Guide, States are benefitting from the investment
in the LTPP program and the results of the LTPP research. And with
traffic volume having increased 68 percent between 1980 and 1997,
while capacity resulting from new roads only grew 4 percent during
the same time period, States' need for longer lasting roads is more
pressing than ever. "LTPP is a valuable research program for
everybody in America-Those who use our roads directly and those who
are the beneficiaries of travel on our roadway systems," says
Francis B. Francois, former Executive Director of AASHTO.
Looking ahead, funding remains a critical issue. The LTPP program's
budget was reduced by about one-third with the passage of the 1998
Transportation Equity Act for the 21st Century (TEA-21). NCHRP funding
approved by States has helped to fill the gap over the past 3 years.
For the LTPP program to fulfill its full potential, however, a larger
investment will be required than that provided by TEA-21. This investment
will provide developers of the next generation of pavement design
procedures with information on the impact of pavement drainage, climatic
factors, traffic, and new pavement design features not available today.
"To me it is very, very important that LTPP continues even beyond
its intended life right now and that its funding be increased,"
says Witczak. "I think it's that valuable."
Other
articles in this issue:
A
new approach for construction workforce training and certification
Keeping
good roads good
The
next generation of technology
Reaping
the benefits of the LTPP investment
Data
integration: Key to practice of asset management
Highway
technology calendar
Join
the Exchange