Transportation Infrastructure: Highway Pavement Design Guide Is Outdated
(Letter Report, 11/21/1997, GAO/RCED-98-9).
A road test conducted by the American Association of State Highway
Officials in 1959-60 found that heavy trucks cause more highway pavement
damage than do other vehicles. On the basis of this test, the
Association developed an initial pavement design guide in 1961, which
has been updated periodically since then. The Federal Highway
Administration (FHWA) has neither adopted the guide nor mandated its use
by states. Rather, FHWA requires that sound engineering and management
principles and practices be used in pavement design. This report (1)
describes the roles of FHWA and others in developing and updating the
pavement design guide and (2) examines the use and the potential of a
computer analysis method known as the nonlinear 3 dimensional-finite
element method for improving the design and the analysis of highway
pavement structures.
--------------------------- Indexing Terms -----------------------------
REPORTNUM: RCED-98-9
TITLE: Transportation Infrastructure: Highway Pavement Design
Guide Is Outdated
DATE: 11/21/1997
SUBJECT: Highway engineering
Highway planning
Highway safety
Road construction
Highway research
Statistical methods
Computer modeling
IDENTIFIER: Three Dimensional Finite Element Pavement Analysis Method
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GAO/RCED-98-9
Cover
================================================================ COVER
Report to the Secretary of Transportation
November 1997
TRANSPORTATION INFRASTRUCTURE -
HIGHWAY PAVEMENT DESIGN GUIDE IS
OUTDATED
GAO/RCED-98-9
Highway Pavement Design Guide
(342929)
Abbreviations
=============================================================== ABBREV
AASHTO - American Association of State Highway Transportation
Officials
DOT - U. S. Department of Transportation
FHWA - Federal Highway Administration
NCHRP - National Cooperative Highway Research Program
TRB - Transportation Reasearch Board
3D-FEM - 3 Dimensional-Finite Element Method
NCHRP/TRB -
Letter
=============================================================== LETTER
B-275328
November 21, 1997
The Honorable Rodney E. Slater
The Secretary of Transportation
Dear Mr. Secretary:
The National Highway System encompasses about 155,000 miles of the
nation's most important interstate, arterial, and major highways and
freeways, which represents about 4 percent of the nation's
approximately 4 million miles of public roads. Billions of dollars
have been spent to construct these roads and highways, and preserving
and maintaining them is estimated to cost billions of dollars more
each year. In 1995, the U.S. Department of Transportation (DOT)
estimated that the average annual cost to maintain overall highway
conditions and performance for this system through the year 2013 to
be $44.8 billion.\1
An American Association of State Highway Officials\2 road test
conducted in 1959-60 to obtain pavement performance data
showed--among other things--that heavy trucks cause more highway
pavement damage than other vehicular traffic. On the basis of this
test, the Association developed an initial pavement design guide in
1961, and it has been updated periodically since then. DOT's Federal
Highway Administration (FHWA) neither adopts the guide nor requires
its use by states. Rather, FHWA--in its working relationship with
states--requires that sound engineering and management principles and
practices be used in the pavement design process. According to FHWA,
one indication of this is the states' use of guides and standards
developed by a number of standard-setting industry organizations,
including AASHTO.
This report (1) describes the roles of FHWA and others in developing
and updating the pavement design guide and (2) examines the use and
potential of a computer analysis method known as the nonlinear 3
Dimensional-Finite Element Method (3D-FEM)\3 for improving the design
and analysis of highway pavement structures.
--------------------
\1 1995 Status of the Nation's Surface Transportation System:
Condition and Performance, DOT (Washington, D.C.: Oct. 27, 1995),
pp. xix, 175.
\2 This organization has since become the American Association of
State Highway and Transportation Officials, more commonly known as
AASHTO.
\3 The nonlinear 3D-FEM method uses a set of computer programs to
analyze engineering problems. It has been used for about 25 years
for solving structural problems with complicated geometries,
loadings, and material properties associated with aeronautical,
biomedical, automotive, naval architecture, nuclear weaponry,
off-shore drilling, piping, and seismic engineering.
RESULTS IN BRIEF
------------------------------------------------------------ Letter :1
The Federal Highway Administration has worked cooperatively with the
American Association of State Highway and Transportation Officials in
developing and updating the pavement design guide. The current guide
is slated to be updated by the year 2002 to better reflect the
changing priority of rehabilitating the nation's highways rather than
building new ones. In contrast to the current guide that many
transportation experts believe is outdated, the new guide is expected
to incorporate the use of analytical methods to predict pavement
performance under various loading and climatic conditions. Sponsors
believe that "a new design approach will more realistically
characterize existing highway pavements and improve the reliability
of designs."
A promising analytical method to accurately predict pavement response
is the nonlinear 3 Dimensional-Finite Element Method. Only with
accurate response data can one reliably predict pavement performance.
The use of this method has the potential to improve the design of
highway pavements--which encompasses their safety, durability, and
cost-effectiveness--because values of stresses, strains, and
deflections (pavement response) can be calculated accurately from a
variety of static, impact, vibratory, and moving mixes of traffic
loads. Several state departments of transportation, academicians,
and scientists have pioneered the use of the nonlinear 3
Dimensional-Finite Element Method and are using it to solve a variety
of complex structural engineering problems, including the design and
analysis of highway pavement structures. While this is a promising
method for improving highway pavement design and analysis, we could
find no evidence that it is being considered for inclusion in the
current design guide update.
BACKGROUND
------------------------------------------------------------ Letter :2
FHWA is responsible for administering and overseeing various highway
transportation programs, including the Federal-Aid Highway
Program--which provides financial assistance to the states for
improving the efficiency of highway and traffic operations. FHWA
relies on AASHTO to (1) provide technical guidance for the design,
construction, and maintenance of highways and other transportation
facilities; (2) publish manuals, guides, and specifications regarding
design, safety, maintenance, and materials; and (3) conduct planning
for highways, bridges, and other structures. Active membership in
AASHTO is open to the state departments of transportation of the
United States, Puerto Rico, and the District of Columbia. DOT is an
active, albeit nonvoting, member. FHWA supports AASHTO's manuals,
guides, and specifications, which the states can use in designing and
analyzing federally funded highway projects. In addition, states can
use their own pavement design criteria and procedures for such
projects, which generally mirror what is in AASHTO's pavement design
guide.
UPDATING THE PAVEMENT DESIGN
GUIDE
------------------------------------------------------------ Letter :3
Currently, highway pavement design criteria and procedures are
documented in AASHTO's 1993 Guide For the Design of Pavement
Structures. AASHTO's Joint Task Force on Pavements is responsible
for the development and updating of the guide. The guide was first
issued in 1961 and then updated in 1972, 1981, 1986, and 1993.
Another update of the guide is forthcoming. The task force's efforts
to update the guide are overseen by a National Cooperative Highway
Research Program (NCHRP) project panel, which functions under the
Transportation Research Board (TRB) of the National Academy of
Sciences' National Research Council.
While constructing new highways was once the primary goal of state
transportation departments, the major emphasis in pavement design in
the 1990s has progressed to rehabilitating existing highways.
According to NCHRP, the current guide does not reflect this shift in
emphasis, and the updated guide is the expected product of an
NCHRP/TRB contract with an engineering consulting firm that is
expected to be awarded in the near future. Under the contract, the
guide would be updated by 2002. In updating the guide, NCHRP intends
to improve upon the outdated pavement design procedures contained in
the current guide.
The current design guide and its predecessors were largely based on
design equations empirically derived from the observations AASHTO's
predecessor made during road performance tests completed in 1959-60.
Several transportation experts have criticized the empirical data
thus derived as outdated and inadequate for today's highway system.\4
\5 In addition, a March 1994 DOT Office of Inspector General report
concluded that the design guide was outdated and that pavement design
information it relied on could not be supported and validated with
systematic comparisons to actual experience or research.\6 In
contrast to the current guide, which relied heavily on an empirical
approach to derive its design equations, the NCHRP contract to update
the guide by 2002 calls for the use of an approach that would more
realistically characterize existing highway pavement usage and
improve the reliability of designs.
Under the first phase of the contract that ended in July 1997,
Nichols Consulting Engineers developed a detailed work plan for
completing the new pavement design guide. When the project manager
resigned in June 1997, NCHRP decided to rebid the contract. The
NCHRP program officer stated that he believes that the new guide will
be completed as planned.
--------------------
\4 Kenneth A. Small, Clifford Winston, and Carol Evans, Road Work,
The Brookings Institution (Washington, D.C.: 1989), pp. 26-27.
\5 Jerry J. Hajek, General Axle Load Equivalency Factors, Ontario
Ministry of Transportation, Downsview, Ontario, Canada, TRB,
Transportation Research Record No. 1482 (Washington, D.C.: 1995).
\6 Report on Audit of Cost Comparison of Asphalt Versus Concrete
Pavement, DOT Office of Inspector General, FHWA Region 4, Report
Number R4, FH-4-008 (Mar. 30, 1994).
AN EXISTING PAVEMENT DESIGN AND
ANALYSIS METHOD HAS THE
POTENTIAL TO IMPROVE HIGHWAYS
AND IS BEING USED BY OTHERS
------------------------------------------------------------ Letter :4
An existing method called nonlinear 3D-FEM has the potential to
significantly improve the design and analysis of highway pavement
structures. A number of nonlinear 3D-FEM computer programs have been
available since the 1970s that can be used for solving complex
structural engineering problems, including designing safer,
longer-lasting, more cost-effective highway pavement structures.\7
Nonlinear 3D-FEM is considered by many experts to be superior to
current design and analysis methods because values of stresses,
strains, and pavement deflections can be calculated accurately from a
variety of traffic loads--static, impact, vibratory, and moving mixes
of traffic loads, including multiaxle truck/trailer loads both within
and outside legal weight limits. The nonlinear 3D-FEM analysis
allows a level of detail that aids in selecting pavement materials as
well as improving the accuracy of determinations of the thickness
needed for new, reconstructed, and overlay pavements. This method
can be used to analyze pavements for strengthening that may be
required for expected traffic loads in the future and for computing
the pavements' remaining structural and operational lives.
Several highway departments and academic institutions have already
used nonlinear 3D-FEM for various structural analysis applications.
The Indiana, Mississippi, and Ohio departments of transportation, for
example, have pioneered the use of nonlinear 3D-FEM in pavement
design and analysis. Officials of these agencies told us that they
are very satisfied with its application on various road systems.
In 1995, the University of Mississippi used nonlinear 3D-FEM to
analyze jointed concrete pavement for dynamic truck loads and thermal
analysis.\8 An official from the Mississippi State Department of
Transportation told us that this method enabled the state to
determine the conditions causing the rapid deterioration of its
concrete pavement. Similarly, a senior scientist from a firm
specializing in evaluating the integrity of engineering structures
told us that, among other things, the finite element method--combined
with statistical theory (which factors in uncertainties in material
properties)--has been used to predict the expected life of a concrete
runway at Seymour Johnson Air Force Base in North Carolina.
Because it considers AASHTO's pavement design guide to be outdated,
the School of Civil Engineering, Purdue University, also has been
using nonlinear 3D-FEM to analyze various pavement problems. The
university has used this method to analyze responses to moving
multiaxle truck/trailer loads within and outside legal weight limits
on both flexible and rigid pavements. Studies the university has
conducted to verify the analyses have shown a strong correlation
between field and predicted pavement responses (strains and
deflections).\9
More recently, Purdue University conducted a study--including the use
of field instrumentation, laboratory testing, field data collection,
and subgrade and core sampling--of three asphalt pavement sections
with different subdrainage configurations on a portion of Interstate
469 in Ft. Wayne, Indiana.\10 Nonlinear 3D-FEM was used to evaluate
the subdrainage performance and the analysis of moisture flow through
the pavement. The results of the study indicated a strong
correlation between the predicted and field-measured outflows of
water.
The effects of high moisture conditions on pavement performance
include rutting, cracking, and faulting--leading to increased
roughness, unsafe conditions, and a loss of serviceability. A
pavement design manager with the Indiana Department of Transportation
told us that the Purdue study, using nonlinear 3D-FEM, confirmed that
the Department's previously used subdrainage design procedures
resulted in a drainage outflow pipe that was too small--thus limiting
moisture outflow. Subdrainage layers with filter layers, a
perforated pipe (subdrainage collector pipe), trench material, and an
outlet pipe play a key role in reducing the extent and duration of
high moisture conditions in pavement structures and their subgrade.
The manager said that nonlinear 3D-FEM provided the (1) proper
(increased) size of drainage outlet pipe and (2) best, most efficient
filter material, which turned out to be less costly than the material
previously being used. We were told that Indiana's Transportation
Department is now in the process of adopting nonlinear 3D-FEM as its
preferred method for designing subdrainage systems. An Indiana
research section engineer also told us that he believes that
nonlinear 3D-FEM could be used by all state highway departments to
design subdrainage systems.
Battelle Memorial Institute recently applied nonlinear 3D-FEM to
predict pavement response to a broad range of vehicle loads on 4
miles of newly constructed highway pavement (2 miles southbound and 2
miles northbound) north of Columbus, Ohio. According to a Battelle
project scientist and an academician from Ohio University, the
results of the heavily instrumented highway test sections showed a
strong correlation with the analytical results achieved from
nonlinear 3D-FEM.\11 They also told us that nonlinear 3D-FEM is the
best computational method to address pavement problems. A chief
engineer of the Ohio Transportation Department further told us that
the state was pleased with Battelle's efforts to predict pavement
response using the nonlinear method.
According to an engineer-advisor with the DOT Inspector General's
Office, AASHTO's pavement design guide has changed very little over
the years. He was of the opinion that new design procedures are
needed, incorporating nonlinear 3D-FEM, if FHWA and the states are
going to be better able to ensure that highway pavement is
constructed, reconstructed, or overlaid according to current FHWA
policy that it be safe, durable, and cost-effective.
We reviewed the scope of work of the contract NCHRP awarded in
December 1996 to Nichols Consulting Engineers for the development of
the new guide. The scope of the most recent contract work does not
directly cite nonlinear 3D-FEM as a technique that can be used in the
design and analysis of highway pavement. In discussions with
Nichols' project manager and with an NCHRP official and in our review
of the contractor's work plan for the guide, we did not find any
specific reference that nonlinear 3D-FEM would be investigated for
inclusion or exclusion in the 2002 update. Through interviews with
FHWA, AASHTO, and NCHRP officials, we attempted to determine why the
method was not specifically being considered. We did not receive any
explanation. However, the program officer said that while the
contractual documentation for this particular effort does not contain
specific reference to nonlinear 3D-FEM as a pavement design and
analysis method, the documentation does not exclude the use of such a
method either.
--------------------
\7 Dr. John Hallquist, formerly of the Lawrence Livermore National
Laboratory, Livermore, California, developed the nonlinear 3D-FEM
computer programs DYNA-3D in 1976 and NIKE-3D in 1978. Lawrence
Livermore used these nonlinear 3D-FEM programs to analyze the effects
of nuclear explosive devices underground and the ability of
intercontinental ballistic missiles to penetrate hardened military
structures. Improved versions called LS-DYNA-3D and LS-NIKE-3D have
become available since 1989 and 1995 from Dr. Hallquist, Livermore
Software Technology Corporation, 2876 Waverely Way, Livermore,
California 94550. The nonlinear 3D-FEM computer program ABAQUS has
been available since 1978 from Hibbitt, Karlsson and Sorensen, Inc.,
1080 Main Street, Pawtucket, Rhode Island 02860.
\8 Three Dimensional-Finite Element Analysis of Jointed Concrete
Pavement, Waheed Uddin, Robert M. Hackett, Ajith Joseph, Zhou Pan,
Department of Civil Engineering, University of Mississippi, and A.B.
Crawley, Mississippi Department of Transportation, TRB,
Transportation Research Record No. 1482 (Washington, D.C.: 1995).
\9 Sameh Zagloul and Thomas D. White, Effect of Overload Vehicles on
the Indiana Highway Network, School of Civil Engineering, Purdue
University, Joint Highway Research Project (FHWA/IN/JHRP-93-5)
(IN47907, June 2, 1994).
\10 Hossam F. Hassan and Thomas D. White, Locating the Drainage
Layer for Flexible Pavements, School of Civil Engineering, Purdue
University, Joint Highway Research Project (FHWA/IN/JHRP-96/14) (IN
47907, Dec. 1996).
\11 James C. Kennedy, Jr., Pavement Response to Vehicular Roads--A
Mechanistic Approach Involving Nondestructive Evaluation Techniques,
Battelle Memorial Institute, Columbus, Ohio, Proceedings:
International Society for Optical Engineers, Nondestructive
Evaluation Techniques for Aging Infrastructure and Manufacturing,
Scottsdale, Arizona (Dec. 2-5, 1996).
CONCLUSIONS
------------------------------------------------------------ Letter :5
The pavement design guide developed and updated by AASHTO over the
years for designing and analyzing highway pavement structures is
outdated. NCHRP has undertaken a 5-year effort to update the guide
employing improved design approaches. Research on nonlinear 3D-FEM
and documented successes in its application suggest that this method
could be an important tool for accurately (1) designing and analyzing
new highway pavement structures and (2) analyzing the response of
deteriorated pavement structures for rehabilitation. We believe it
should be considered in NCHRP's ongoing efforts to update AASHTO's
current pavement design and analysis guide. The recent decision to
rebid the contract for the design guide update provides an
opportunity for FHWA to specify the consideration of this method.
RECOMMENDATION
------------------------------------------------------------ Letter :6
To better assist states in designing safer, longer lasting, and more
cost-effective new, reconstructed, and overlay highway pavement
structures, we recommend that the Secretary of Transportation direct
the Administrator, FHWA, to ensure that nonlinear 3D-FEM is
considered in the current update of the pavement design guide.
AGENCY COMMENTS AND OUR
EVALUATION
------------------------------------------------------------ Letter :7
We provided a draft of this report to DOT for its review and comment.
In written comments dated October 31, 1997 (see app. II), DOT stated
that it has maintained a long- standing commitment to ensuring that
the nation's investment in its highway infrastructure is
cost-effective. DOT concurred with our recommendation that nonlinear
3D-FEM be considered in the current update of AASHTO's pavement
design guide. DOT stated that it would work with NCHRP to encourage
full consideration of the method along with other quantitative
analytical methods.
As part of its commitment to a cost-effective highway infrastructure,
DOT stated that FHWA has supported research efforts at its own
Turner-Fairbank Highway Research Center as well as efforts by AASHTO,
NCHRP, and TRB. DOT further stated that FHWA is fully aware of and
recognizes the potential benefits to highway design offered by
3D-FEM. According to DOT, FHWA has supported the development of this
technology at its Turner-Fairbank facility and with individual states
through the State Planning and Research program. DOT stated that
FHWA considers 3D-FEM to be a very useful research tool for analyzing
pavement structures but that it will be up to NCHRP and AASHTO to
determine whether the method has achieved the maturity necessary to
become a practical engineering tool.
We are pleased to hear of DOT's interest in and acceptance of
nonlinear 3D-FEM as an analytical tool for designing and analyzing
highway pavement structures. Such interest and acceptance was never
made known to us (1) during discussions we had with the Chief,
Pavement Division, FHWA; the project manager, AASHTO; a senior
program officer, NCHRP; and the initial contractor's project manager
for the development of the 2002 pavement guide nor (2) in
documentation we gathered and reviewed during the assignment.
We made other clarifying changes to the report as appropriate on the
basis of other comments by DOT.
---------------------------------------------------------- Letter :7.1
We performed our work from May 1996 through October 1997 in
accordance with generally accepted government auditing standards.
Appendix I contains details on our objectives, scope, and
methodology.
As you know, 31 U.S.C. 720 requires the head of a federal agency to
submit a written statement of the actions taken on our
recommendations to the Senate Committee on Governmental Affairs and
to the House Committee on Government Reform and Oversight not later
than 60 days from the date of this letter and to the House and Senate
Committees on Appropriations with the agency's first request for
appropriations made more than 60 days after the date of this letter.
We are sending copies of this report to the Administrator, FHWA; the
Director, Office of Management and Budget; and appropriate
congressional committees. We will make copies available to others
upon request.
Please call me at (202) 512-2834 if you have any questions. Major
contributors to this report are listed in appendix III.
Sincerely yours,
John H. Anderson, Jr.
Director, Transportation Issues
OBJECTIVES, SCOPE, AND METHODOLOGY
=========================================================== Appendix I
The objectives of this review were to (1) describe the roles of the
Federal Highway Administration (FHWA) and others in developing and
updating the pavement design guide and (2) examine the use and
potential of a computer analysis method known as the nonlinear 3
Dimensional-Finite Element Method (3D-FEM) for improving the design
and analysis of highway pavements.
To accomplish these objectives, we first reviewed the American
Association of State Highway and Transportation Officials' (AASHTO)
highway pavement guide, which is being used by many state departments
of transportation as an aid in designing and analyzing pavement
structures, federally funded and otherwise. We reviewed available
literature and contacted officials from FHWA, AASHTO, and the
Transportation Research Board. We also contacted contractor
officials responsible for the development and updates of the pavement
design guide. We contacted officials from the Transport Research
Laboratory, Crawthorne, Berkshire, United Kingdom, and reviewed its
pavement design practices. We contacted officials from the U.S.
Army Engineer Waterways Experiment Station, Vicksburg, Mississippi;
Indiana, Mississippi, and Ohio state highway departments; and various
engineering consulting firms. We contacted academicians from the
University of Arizona, the University of Cincinnati, Florida A&M
University-Florida State University, Ohio University, the University
of Iowa, the University of Mississippi, the University of Nebraska,
and Purdue University, as well as Birmingham University in the United
Kingdom. Also, we contacted scientists from Battelle Memorial
Institute and Lawrence Livermore National Laboratory.
We selected these educational institutions and nonprofit
organizations because all have conducted research and development
work related to pavement design and analysis and/or the application
of nonlinear 3D-FEM for solving structural engineering problems.
Furthermore, we performed a literature and database search to
identify any individuals who have authored publications on the
applications of nonlinear 3D-FEM to highway pavement design and
analysis or other structural engineering problems.
We discussed with FHWA and others their roles in keeping up with and
promoting up-to-date techniques regarding pavement design and
analysis. We reviewed FHWA's pavement policy issued in December
1996, which states that pavements should be designed to accommodate
current and predicted traffic needs in a safe, durable, and
cost-effective manner.
More broadly, we used in this review information we obtained through
attendance at the Fourth International Conference on the Bearing
Capacity of Roads and Airfields held in July 1994 in Minneapolis,
Minnesota; the Third Materials Engineering Conference held in
November 1994 in San Diego, California; annual Transportation
Research Board meetings held in January 1995 and in January 1997 in
Washington, D.C.; and the Structures Congress XV held in April 1997
in Portland, Oregon.
(See figure in printed edition.)Appendix II
COMMENTS FROM THE DEPARTMENT OF
TRANSPORTATION
=========================================================== Appendix I
(See figure in printed edition.)
(See figure in printed edition.)
MAJOR CONTRIBUTORS TO THIS REPORT
========================================================= Appendix III
RESOURCES, COMMUNITY, AND ECONOMIC
DEVELOPMENT DIVISION
Dr. Manohar Singh, P.E., Engineering Consultant
Ralph W. Lamoreaux, Assistant Director
*** End of document ***