May/June
2002
Benefitting
from LTPP—A State's Perspective
by
Gary Hoffman
Pavements
are where the proverbial rubber meets the road. For more than a decade
now, the States, Federal Government, and the Canadian provinces have
invested in the Long Term Pavement Performance Program (LTPP), a 20-year
pavement research project. During its first 10 years, LTPP gathered,
processed, and analyzed data describing the structure, service conditions,
and performance of more than 2,500 pavement test sections in North
America.
Why the
investment in this program? What are the values and benefits of LTPP
to date? At the Transportation Research Board's (TRB) 2002
Annual Meeting, I addressed these questions from a State's perspective.
Following are highlights from my presentation to the TRB audience.
Benefits
of LTPP to Date
In the
long run, the most important benefit of LTPP is the database. It is
an unprecedented resource that will provide the pavement performance
data needed to answer all kinds of questions—even those we have
not yet conceived.
The more
visible LTPP products and findings that benefit Pennsylvania are in
some sense old news, but their
value and importance has not diminished. One benefit is calibration
procedures for falling weight deflectometers (FWDs) and FWD calibration
centers.
Calibrating
FWDs
Falling
weight deflectometers measure the structural condition of a pavement,
and most States have been using the equipment for some time. It was
not until the late 1980s, however, that LTPP developed FWD calibration
procedures. These procedures are the only nationally accepted means
of verifying that FWD information is accurate. Subsequently,
LTPP opened four FWD calibration centers in cooperation with State
departments of transportation (DOTs) in Minnesota, Nevada, Pennsylvania,
and Texas.
2002
Design Guide
The
American Association of State
Highway and Transportation Officials' (AASHTO) Guide for the
Design of Pavement Structures is widely used in the design of
new and rehabilitated highway pavements. However, the current
Design Guide, published in 1993, is broadly recognized as being
inadequate for the design challenges currently faced by highway
agencies. To address the inadequacies, the National Cooperative
Highway Research Program undertook a project called "Development
of the 2002 Guide for the Design of New and Rehabilitated Pavement
Structures," otherwise known as the 2002 Design Guide.
The
importance of LTPP to the development
of the 2002 Design Guide was recognized from the very start.
LTPP data document the performance of an extensive array of
pavement designs, in a wide range of service conditions, making
possible the calibration and validation of broadly applicable
models to predict pavement performance. The models are key elements
in pavement design procedures. The LTPP database also provides
a strong basis for the development of guidelines for the selection
of default or typical values for design inputs.
In
addition, LTPP is providing one of the most important elements
in technology development through field calibration and validation.
The use of LTPP data helps demonstrate to the user community
that the models and technologies being developed match real-world
pavement performance. This applicability, in turn, helps encourage
the States to adopt new technologies and approaches. Given the
funds spent on highways—in 1995 highway agencies spent
approximately $17 billion on pavement-related projects, according
to FHWA's 1999 Highway Statistics—it is extremely important
that the 2002 Design Guide be accurate and up-to-date, and reach
mainstream audiences for implementation as soon as possible.
Developers of the 2002 Design Guide estimated that the new procedures
could result in savings of nearly $1 billion annually on pavement
rehabilitation.
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Calibration
centers help ensure that Pennsylvania's pavement designs and rehabilitation
strategies are based on the most accurate data possible. With the
dollars that Pennsylvania spends each year on rehabilitating our roads,
we need the most accurate data we can get.
![Photo of a Long Term Pavement Performance Falling Weight Deflectometers is collecting deflection data from an LTPP test section](images/09pict1.jpg) |
One
of the Long Term Pavement Performance Falling Weight Deflectometers
is collecting deflection data from an LTPP test section.
|
In recent
years, use of the calibration centers has been on the rise. In 2000,
the four FWD calibration centers were used to calibrate a total of
79 FWDs, including 57 owned by State highway agencies. With the anticipated
delivery of AASHTO's 2002 Guide for the Design of Pavement Structures
(see "2002 Design Guide" on page 47) and increased focus
on mechanistic-empirical design principles, use of the FWD calibration
centers is expected to increase.
FWD calibration
centers help States like Pennsylvania obtain accurate data, resulting
in better decisions about when and where to conduct rehabilitation
work, how to use budget dollars more cost effectively, and how to
make better decisions when designing new pavements and overlays.
A
New View on Skewed Joints
LTPP
studies on the efficacy of skewed joints provided the information
needed to support a cost-saving change in Pennsylvania's policy on
joints.
The studies
analyzed LTPP data to identify what worked and what did not control
the development of joint faulting. Based on PennDOT's review of the
studies, the Commonwealth decided to change its practice of using
skewed joints.
Pennsylvania
will be able to reduce costs initially because perpendicular joints
are less expensive than skewed joints. In addition, we believe the
Commonwealth will save money by eliminating construction problems
and ensuring that future maintenance is easier. Not only will we save
money initially, but also throughout the entire life cycle of a pavement
project.
LTPP's
analysis program addresses a broad array of topics, from field validation
of pavement design procedures and studies of variability in traffic
and materials data to investigating the development of pavement roughness.
In turn, findings from these analyses provide key information that
helps highway engineers in their day-to-day operations.
2002
Guide Implementation
Pennsylvania
is also relying on LTPP products and the LTPP database as the Commonwealth
begins implementing the principles outlined in the 2002 Guide for
the Design of Pavement Structures. Specifically, Pennsylvania has
started to take advantage of improvements in resilient modulus testing
that came about as a result of LTPP.
![Photo of van Dynatest Falling Weight Deflectometer](images/09pict2.jpg) |
The
Long Term Pavement Performance Program is transporting a Dynatest
Falling Weight Deflectometer.
|
The resilient
modulus—or stiffness of the soil and rock in the subgrade at
a paving project—is a critical factor in determining the thickness
and composition of pavement layers. Resilient modulus testing is a
standardized laboratory procedure
for measuring the resilient modulus of subgrade materials, along with
a related laboratory startup and calibration verification procedure.
For years,
measuring the resilient modulus of a particular site was at best a
complex and difficult task, but using LTPP data, it is expected that
the process will become a great deal easier. AASHTO has adopted the
LTPP resilient modulus procedures as a provisional standard.
LTPP
data will be used to validate the 2002 Guide for Pennsylvania conditions.
Highway engineers may find it useful to employ the LTPP data from
their own State to test the applicability of general models to the
unique conditions on their particular roads.
![An aerial photo showing the John J. Shumaker Memorial Highway,](images/09pict3.jpg) |
This
aerial photo shows the John J. Shumaker Memorial Highway, a
bypass around Dauphin Borough in Dauphin County, Pennsylvania.
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Asset
Management
LTPP
provides the data necessary to support pavement performance models
that help engineers and planners
develop reliable predictions regarding the resources required for
efficient highway maintenance, rehabilitation,
and construction strategies.
The
LTPP Story
The need for the LTPP was identified
in the "infrastructure crisis" of the early to mid-1980s. Pavements were simply
not living up to expectations. LTPP was initiated in 1987 as
part of the Strategic Highway Research Program.
LTPP
has six program objectives. The first five can be summarized
as providing factual and accurate answers as to how and why
pavements perform as they do. The
sixth goal is the creation of a national LTPP database to support
objectives 1-5.
LTPP
monitors approximately 2,500 sections of pavement sections across
the United States and Canada. Of these, 780 were selected from
existing highway pavements and are the subjects of LTPP General
Pavement Studies (GPS). The remaining sections were constructed
by State highway agencies for LTPP Specific Pavement Studies
(SPS).
Data
collection on the GPS sections began in 1989, while the SPS
data collection started in the early 1990s. The collected data
characterize climatic conditions, material properties, traffic
volumes and loads, pavement layer thicknesses, and pavement
performance. LTPP uses extensive quality control and quality
assurance measures to achieve complete, accurate, and consistent
results.
With
the conclusion of the Strategic Highway Research Program
in 1992, FHWA agreed to
take over operation of LTPP. To maintain State, industry, and
academia ownership, involvement, and input, FHWA asked the Transportation
Research Board (TRB) to create a TRB-LTPP committee. The 15-member
committee is chaired by a State chief administrative officer,
with seven of the members drawn from the State DOTs.
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For asset
management, the wealth of data available in the LTPP database
provides a strong foundation for developing empirical performance
prediction models. Similarly, LTPP data also offers a strong foundation
for the evaluation, validation, and verification of empirical or mechanical
models.
Benefits
in 2001
Throughout
2001 the opportunities to benefit from LTPP continued to grow. Specifically:
- The
release of DataPave 3.0 software, which provides quick access to
most of the LTPP data, makes it easier for everyone to benefit from
this valuable resource.
- LTPP
findings regarding the adequacy of 3- and 5-point rut bar data helped
Pennsylvania's neighbor New York make informed decisions in its
specification of a data collection vehicle.
- The
release of LTPP findings on the topic of pavement smoothness—arguably
the most important measure of performance to highway users—provided
the basis for new smoothness index relationships developed for use
in construction quality control.
- Both
the AASHTO Subcommittee on Materials and the American Society for
Testing and Materials (ASTM) balloted LTPP-based standards for temperature
correction of FWD test results.
LTPP
Benefits All of Us
Although
the transportation community cannot and should not expect LTPP to
be the solution to all of its problems, the industry can rely on it
as a preeminent source of pavement performance
data, answering all kinds of questions yet to be conceived.
The number
of ways in which States can benefit from LTPP continues to grow, but
the extent to which the transportation community benefits will depend
on the investment made in learning about, testing, and applying the
findings and products of LTPP.
The exact
relationship between the investments made in LTPP and the benefits
accrued is difficult to calculate. However, what we do know is that
if we do not seize the opportunity to invest in learning about, adopting,
adapting, and applying the findings and products of LTPP, we will
not achieve all the benefits that are possible.
One of
the Long Term Pavement Performance Falling Weight Deflectometers is
collecting deflection data from an LTPP test section.
![Photo of State Route 79 in Allegheny County, Pennsylvania](images/09pict4.jpg) |
State
Route 79 in Allegheny County, Pennsylvania.
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Gary
L. Hoffman, P.E., was appointed to the position of chief engineer
of highway administration for the Pennsylvania Department of Transportation
(PennDOT) on June 26, 1995. As chief engineer, he directs a team of
more than 650 employees involved with the maintenance, operations,
restoration, and expansion of Pennsylvania's transportation infrastructure.
The focus of his organization is setting policy and standards, performing
quality assurance, identifying and implementing technological change,
and providing for development of the technical workforce. Chief Engineer
Hoffman is a licensed professional engineer and surveyor with more
than 33 years of experience, 29 of which have been with PennDOT. He
has steadily moved through the ranks at PennDOT serving as director
of maintenance and operations prior to his appointment as chief engineer.
From 1983 to 1992, Hoffman was the director of the Bureau of Bridge
and Roadway Technology where he was contract manager for developing
the department's RMS, BMS, and NBIS Safety Inspection Systems. Hoffman
received both a B.S. and M.S. in civil engineering from Drexel University
in Philadelphia. He has authored or co-authored more than 40 published
technical papers and articles, primarily in the areas of transportation
materials, pavement designs, construction practices, and management
systems. Many of these papers and articles have received national
exposure. Hoffman is active in strategic planning and innovation implementation
at the national level and serves as chairman or as an active member
of several National Academy of Science- and AASHTO-sponsored boards
and committees. He chairs the new AASHTO Committee on Technology Implementation,
is a vice-chair of the Subcommittee on Maintenance, and chairs the
Task Force on Retroreflectance of Signs and Markings. He is a member
of AASHTO's Asset Management Committee of AASHTO's Land Transportation
Security Task Force and the National Partnership for Highway Quality
and is an active participant in the Standing Committee on Highways.
He is also a member of the TRB Steering Committee on Long Term Pavement
Performance and the TRB Committee for Research on Improved Concrete
Pavements.
Other
Articles in this issue:
Arizona
Tackles Work Zone Delays
A
Hallmark of Context-Sensitive Design
Safer
Roads Thanks to ITS
Do
Better Roads Mean More Jobs?
Exciting
Opportunity for ITS Work
See
It Before It's Built
Roadway
Lighting Revisited
The
Man Who Loved Roads
Benefitting
from LTPP—A State's Perspective