November/December 2002
Digging into LTPP Pavement Data
by Antonio Nieves Torres and John J. Sullivan
IV
What can you do with the most extensive pavement study ever
conducted? That's the question Roger Smith, associate professor at
Texas A&M University, asks the students in his pavement engineering
courses as they begin working with the Long-Term Pavement Performance
(LTPP) database.
Smith and other faculty members in the United States and internationally
recognize the unique value of the LTPP database to the pavement industry.
The world's largest collection of pavement performance data ever compiled,
the database contains nearly two decades of data on climate, materials
tests, maintenance, rehabilitation, traffic, and pavement monitoring.
"We use the LTPP database as an exploratory data set," Smith says.
"It gives us the data to develop the concepts and processes when we
don't have the real data from a particular agency."
![DataPave 3.0 logo on cd](images/06nieves1.jpg)
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Each participant in the 2002 International Contest on LTPP
Data Analysis received a copy of DataPave 3.0, a CD-ROM containing
the most recent LTPP data.
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To encourage greater use of the data to benefit the pavement industry,
the Federal Highway Administration's (FHWA) LTPP product team, led
by Monte Symons, and an American Society of Civil Engineers (ASCE)
committee, chaired by Professor Fouad Bayomy, teamed up to sponsor
a contest based on LTPP data. The International Contest on LTPP Data
Analysis challenges students and professors from the United States
and around the globe to come up with new and innovative analyses of
the LTPP data. These analyses can enhance industry knowledge, improve
pavement performance, or lead to new pavement technologies.
For the academic year 2001-2002, FHWA and ASCE recognized a total
of five papers. One of Smith's students, for example, submitted a
paper that describes a process for applying LTPP data to help researchers
in California estimate road user costs due to pavement distress. Another
student, from the University of Kentucky, used LTPP data to develop
a climate map that could help highway engineers match pavement design,
construction, and maintenance strategies to regions with similar climate
patterns. Collectively, the winners demonstrate a variety of ways
to use the LTPP data to reveal new insights about pavement performance.
Relating Moisture and Pavement Subgrades
Hassan M. Salem, a Ph.D. student in civil engineering at the University
of Idaho, tied for first place in the graduate student category. Salem
studied the effect of seasonal moisture variation on the resilient
modulus of pavement subgrade soils. The changing seasons can lead
to cracks and ruts in pavements. By developing a seasonal adjustment
factor for the subgrade soil layer beneath asphalt pavements, Salem's
research aimed to help designers determine the subgrade's resilience
during any season and, ultimately, to improve the design of new and
rehabilitated pavements.
Salem extracted elastic moduli, temperature, and moisture data representing
different soil types in non-freeze zones at seven LTPP seasonal monitoring
sites around the United States. After analyzing the data, Salem found
that moisture and resilient modulus follow an almost sinusoidal function
with different months of the year.
Salem, who learned how to use the LTPP database in a class offered
by his advisor, relies on the data as an integral part of his graduate
work. "The enormous quantity of data in the LTPP database can provide
fodder for thousands of research papers—probably enough to keep
a researcher busy for the rest of his life," he says.
![Salem Hassad measures volumetric moisture content at a site in Idaho](images/06nieves2.jpg)
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Moisture content information from the LTPP database helped
first-place winner Hassan Salem determine a seasonal adjustment
factor for pavement subgrade. Here, Salem measures volumetric
moisture content at a site in Idaho.
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Developing Climate Maps
Yuhong Wang, a Ph.D. student in civil engineering at the University
of Kentucky, tied with Salem for first place in the graduate category.
As part of his thesis, Wang used environmental data from the database
to develop a climate map of the United States and Canada, plotting
the LTPP test sections according to their climate patterns.
"A potential use of the climate map," Wang says, "is to help highway
engineers get climate pattern information for their geographical areas
so they can apply the same design criteria, construction requirements,
and maintenance strategies to those regions with similar climate patterns."
Wang selected tables containing climate information from the database,
analyzed the data using clustering methods, and presented his results
on a geographic information system (GIS) map.
For Wang, the database already was contributing to his thesis, and
the contest provided an opportunity to share some of his findings.
"I wanted to get a chance to let other people look at my work and
maybe get some feedback."
![Map of US and Canada with markers for various climate groups](images/06nieves3.jpg)
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First-place winner Yuhong Wang used climate information to
organize test sections from the database into 61 climate groups,
some of which are shown on this map. Test section with similar
numbers tend to have similar climate patterns.
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Converting Distress Data
Shameem A. Dewan, a graduate research assistant at Texas A&M
University, tied for second place in the graduate category. Dewan
developed a method to convert LTPP distress data—such as cracking
and rutting—to a format compatible with a pavement management
system (PMS) developed by the Metropolitan Transportation Commission
(MTC) of Oakland, CA.
"The MTC intended to develop a model for incorporating road user
costs into decisions regarding maintenance and rehabilitation strategies
for city and county streets in the San Francisco Bay area," Dewan
says. "My objective was to estimate road user costs directly from
the MTC-PMS pavement distress information."
Dewan extracted distress data for sites in California from the LTPP
database and established a correlation between pavement distress and
the international roughness index (IRI)—a measure of the roughness
of a road. Since user costs depend on road roughness, Dewan developed
a model for IRI as a function of pavement conditions, which enabled
him to convert the LTPP distress data for use in the MTC-PMS software.
In his research, Dewan found that the LTPP data offered a suitable
proxy for specific data unavailable from State and local agencies
in California. "The cities and counties in the San Francisco Bay area
did not have IRI data for local streets, so I used distress and IRI
data collected from LTPP sites on California's highways and freeways
instead," he says. "Although it would be more appropriate for the
model to use data from city streets, the LTPP data offers a good starting
point. In the future, we can refine the model using data from city
streets."
Dewan first learned about the database while completing his master's
degree. He attended a demonstration on how to extract and use data
from the LTPP database offered by faculty members and FHWA staff members.
He described the database as "very user-friendly once someone helps
you start to use it."
Proofing Family Performance Curves
Mohammed Zulyaminayn, an exchange student from Bangladesh who studied
at Texas A&M University, tied with Dewan for second place in the
graduate category. Zulyaminayn developed a computer program to adjust
performance curves for different groups, or families, of pavements
to better predict the performance of individual pavement sections.
In prior research, Eun Sug Park and Clifford Spiegelman at the Texas
Department of Transportation (TxDOT) developed sets of empirical performance
curves to predict the development of individual types of damage for
different families of pavements. Recognizing that site-specific environmental
conditions and loading patterns cause the performance of individual
pavements to veer from conditions projected by family performance
curves, the Texas Transportation Institute developed an approach to
adjust the projected performance to account for all of the observed
performance data in TxDOT project 4186.
![Photo of rural road with cloudy conditions](images/06nieves4.jpg)
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LTPP climate information can help researchers better understand
how pavements react to environmental conditions such as soil
type, humidity, rainfall, and nearby water sources.
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Examining Influences on As-Built Roughness
Christopher M. Raymond, a Ph.D. candidate in civil engineering at
Canada's University of Waterloo, placed third in the graduate category.
Raymond used LTPP data to determine effects on the as-built roughness
of asphalt overlay pavements. Because pavement roughness is a key
measure of quality, designers and engineers need to understand the
factors that influence the as-built roughness of a pavement so they
can maximize their designs and develop smoothness specifications.
Raymond examined four factors: (1) extent of surface preparation
prior to resurfacing, (2) overlay thickness, (3) type of overlay material,
and (4) pavement roughness prior to resurfacing. Using data extracted
from the LTPP database, he performed various statistical procedures,
including paired data analyses, regression analyses, and a repeated
measures analysis, to investigate the interactive effects. He determined
that factors 1, 2, and 4 have statistically significant effects on
the as-built roughness of a pavement, either directly or interactively
with another variable. The overlay mix type was the only factor he
found not to have an influence on as-built pavement roughness.
Raymond was introduced to the database through a workshop at the 1999
annual conference of the Transportation Association of Canada in St.
John, New Brunswick. "In the area of pavement data, it's hard to obtain
good data," he says. "It would be extremely difficult to coordinate
the data required for my research without the LTPP database."
LTPP in the Classroom
Associate Professor Neeraj Buch and Assistant Professor Karim Chatti,
with the Department of Civil and Environmental Engineering at Michigan
State University, earned first place in the curriculum category for
inclusion of LTPP data in their undergraduate and graduate courses.
The professors found that using the LTPP database as a source for
real pavement data has "enhanced considerably" the quality of their
pavement rehabilitation, design, and analysis courses, according to
Dr. Buch. Previously, in an undergraduate course, Buch and Chatti
used pavement distress data from local and county roads. They found
a number of drawbacks to using local data, including limited distress
types, little or no deflection information, and lack of time series
data. With these shortcomings in mind, the instructors decided to
explore and use the LTPP database as a source of pavement distress
and deflection data, as well as information on traffic growth, pavement
inventory, and climate.
![Photo of Dr. Bayomy teaching a workshop](images/06nieves5.jpg)
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In December 2001, Dr. Fouad Bayomy taught a training workship
at the University of Nevada at Reno on LTPP data analysis.
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"In the past, we tried to create academic problems, but they didn't
relate well to real life because we always found ourselves short of
information," Buch says. "But with the LTPP database, we have real
data—you can't argue with it."
Because of large class sizes in the undergraduate course, rather
than provide direct access to the entire database, the instructors
extract the raw data from the LTPP database and distribute it to small
student groups to analyze. Armed with manageable amounts of raw data—including
pavement geometry, distress, deflection, temperature at the time of
testing, roughness, etc.—the students process the data, determine
the pavement condition, and recommend rehabilitation strategies.
"By the end, the students will be able to recommend rehabilitation
strategies based on the condition of the pavement," Buch says.
While the undergraduate course focuses on rehabilitation exercises,
the graduate course is more analytical. Given the smaller size of
the graduate course, the instructors provide each student with a copy
of DataPave 3.0—a set of two CD-ROMs that include the most recent
LTPP data. After a 2-hour tutorial, the students begin extracting
pavement response and performance data, which they can use to evaluate
existing performance prediction models.
"The LTPP database is such a wealth of meaningful data that graduate
students in pavement engineering cannot afford not to know about it,"
Chatti says. "The possibilities of using the data to investigate different
behaviors of pavement systems are almost endless."
About the Contest
![Photo of Fouad Bayomy](images/06nieves6.jpg)
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Professor Fouad Bayomy chairs the ASCE-LTPP Task Committee.
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FHWAs goal is to expose students—the
future engineers and pavement practitioners—to the variety
of data available in the LTPP database, says Dr. Fouad
Bayomy, chair of the ASCE-LTPP Task Committee that helped launch
the LTPP contest in 1998. With ASCE student chapters in
virtually every university in the United States, ASCE is in
a great position to deliver the data into the students
hands.
A win-win opportunity for all parties, the contest
benefits FHWA by inspiring new transportation products, which
will benefit managers of roadway systems throughout the world.
ASCE stands to gain
new members, and the contest generates a multitude of new papers
for possible publication. Most importantly, the LTPP contest
puts the data in the hands of the students who will be the Nations
future pavement engineers, managers, and administrators.
The partnership between FHWA and ASCE is
a great match, says Aramis Lopez, FHWAs LTPP team
leader. The LTPP contest is a good tool to promote the
use of the LTPP data to reveal new information about pavement
performance.
Students can enter the contest on their own or
with other students in either the Undergraduate or Graduate
categories, or partner with a State highway agency or industry
group in the Partnership category. Students set the research
objectives, conduct the research, analyze the data, and submit
their findings in the form of a paper. The Curriculum category
encourages educators to submit course curricula developed using
LTPP data. All participants receive letters of recognition,
and winners receive
cash prizes, plaques, and certificates. ASCE recognizes the
winners at its annual meeting, and winning papers may be submitted
for publication as well.
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A Golden Research Opportunity
Given four categories—Undergraduate, Graduate, Curriculum, and
Partnership—virtually anyone involved with pavement research,
development, or application can participate in the International Contest
on LTPP Data Analysis. For example, FHWA and ASCE encourage State
departments of transportation and others in the pavement industry
to reach out to up-and-coming pavement engineers and academia through
the Partnership category.
"The goal of the Partnership category," says Dr. Fouad Bayomy, professor
of civil engineering at the University of Idaho and chair of the ASCE
contest committee, "is to encourage State highway agencies and pavement
experts to build or renew ties with local universities. While gaining
valuable experience, student researchers can help agencies develop
innovative solutions to real-world pavement problems."
To encourage further involvement of academia in using the LTPP database,
Bayomy and ASCE's LTPP committee organized a training workshop in
December 2001 at the University of Nevada in Reno to acquaint college
professors with the LTPP program and provide hands-on training with
the DataPave software. The workshop, which was sponsored by FHWA,
attracted more than 20 faculty members from across the country. To
learn more about the workshop or to download the instruction materials,
visit http://www.uidaho.edu/engr/cedept/bayomy/bayomy.htm.
Antonio Nieves Torres is a graduate engineer from the Polytechnic
University of Puerto Rico where he also worked as a professor. Nieves
is a licensed professional engineer in Puerto Rico, and he has worked
as a hydraulics and geometric design engineer in Puerto Rico and Florida.
Over the past 18 years, Nieves has held positions in both the private
and public sectors. A graduate of FHWA's Highway Engineer Training
Program, Nieves has served as a research engineer for the LTPP program
and as the executive director of the Pan American Institute of Highways.
John J. Sullivan IV is a contract writer and assistant editor
for Public Roads magazine.
To learn more about the LTPP program, visit www.tfhrc.gov/pavement/ltpp/ltpp.htm.
For future contest dates, visit www.tfhrc.gov/pavement/ltpp/contest.htm
or contact Antonio Nieves at 202-493-3074 or antonio.nieves@fhwa.dot.gov.
To obtain a free copy of the DataPave 3.0 software or to request technical
support, contact LTPP Customer Support Services at 865-481-2967 or
e-mail ltppinfo@fhwa.dot.gov.
Other
Articles in this issue:
The Scan of the Wild
Filling the Pipeline
TELUS
Measuring the Road to Improvement
Students Grab the Gold Ring
Digging into LTPP Pavement Data
Making It Happen the Fast Way
"Back to Basics" Saves Lives
A Decade of Achievement
Does Your Interchange Design Have You Going Around in Circles?
From Small Beginnings Come Great Things