a

Long-Term Pavement 

Performance Program

Accomplishments and Benefits

1989–2009 
b

Contents

BACKGROUND 1

Program Objectives 1

Test Sections 1

National and Highway Agency Investment 3

Accomplishments and Benefits 3

BENEFITS OF THE LTPP DATABASE 4

Primary Data 4

Ancillary Data 4

Data Accessibility 4

LTPP Data Analysis Program 5

Seasonal Monitoring Program 5

LTPP and the Next Generation of Pavement Professionals 6

ADVANCES IN PAVEMENT PERFORMANCE MEASUREMENT 7

Field Data Collection 7

Quality Control/Quality Assurance 9

CONTRIBUTIONS TO PAVEMENT DESIGN AND MANAGEMENT 12

The Mechanistic-Empirical Pavement Design Guide 12

Evaluation and Modification of Design Methods 14

Improved Predictive Capabilities 15

Understanding Factors That Contribute to Pavement Performance 15

Maintenance and Rehabilitation Insights 16

RETURN ON INVESTMENT 18

LTPP by the Numbers 18

Opportunity Cost 18

Projected Cost/Benefit Ratios 19

THE ROAD AHEAD 21

ENDNOTES 23

ACCESSING LTPP INFORMATION AND PRODUCTS 24

Photo credits: Front and inside front covers, ©istockphoto.com/SandSun. Page 19, istockphoto.com/Tim McCaig. 

All other images, Federal Highway Administration.

Long-Term Pavement Performance Program Highlights 

Accomplishments and Benefits 1989–2009
1

The need for information on how pavements perform 

over time came to the forefront in the early 1980s, as the 

deterioration of highways built two or three decades earlier became a concern for highway agencies. The mission 

to study performance data systematically all across the 

country and to promote extended pavement life was advanced by the National Academy of Sciences Transportation Research Board (TRB), American Association of State 

Highway and Transportation Officials (AASHTO), and 

Federal Highway Administration (FHWA). 

Supported by Congress, the Long-Term Pavement 

Performance (LTPP) program started in 1987, as part of 

the Strategic Highway Research Program (SHRP), a 5-year 

applied research program funded by the 50 States and 

managed by TRB. The LTPP program mission was to 

•	 Collect and store performance data from a large

number of in-service highways in the United States 

and Canada over an extended period to support 

analysis and product development. 

•	 Analyze these data to describe how pavements perform and explain why they perform as they do. 

•	 Translate these insights into knowledge and usable

engineering products related to pavement design, 

construction, rehabilitation, maintenance, preservation, and management. 

Data collection began in 1989. Although SHRP ended as 

planned in 1992, the LTPP program continued under the 

leadership of FHWA, and continues today, with the participation of highway agencies in all 50 States and 10 Canadian Provinces. 

Over a span of 20 years, the LTPP program has monitored the performance of nearly 2,500 in-service pavement test sections throughout the United States and 

Canada representing the wide range of climatic and soil 

conditions on the continent. Test sections are monitored 

until they reach the end of their design life or are otherwise recommended to be taken out of study by the participating agency. By following these pavements over 

time, researchers are gaining insight into how and why 

they perform as they do, which provides valuable lessons on how to build better, longer lasting, more costeffective pavements. 

Program Objectives 

With the goal of extending the life of pavements through 

investigation of the long-term performance of various 

designs of pavements (as originally constructed or rehabilitated) under various conditions, the following objectives were established for LTPP: 

•	 Evaluate existing design methods.

•	 Develop improved design methodologies and strategies for the rehabilitation of existing pavements. 

•	 Develop improved design equations for new and reconstructed pavements. 

•	 Determine the effects of loading, environment, material properties and variability, construction quality,

and maintenance levels on pavement distress and 

performance. 

•	 Determine the effects of specific design features on

pavement performance. 

•	 Establish a national long-term pavement database.

Test Sections 

Test sections are the heart of the LTPP program. The test 

sections were nominated by State and Provincial highway agencies in accordance with statistically sound experimental matrices designed to achieve LTPP program 

BACKGROUND 
2

objectives. The nearly 2,500 test sections, both asphalt 

concrete (AC) and portland cement concrete (PCC), were 

designated throughout all 50 States, Puerto Rico, the District of Columbia, and Canada, as shown in figure 1. 

Each test section is classified as being in either the 

General Pavement Study (GPS) or the Specific Pavement Study (SPS) category. GPS test sections were usually selected from in-service pavements designed and 

built according to good engineering practice by departments of transportation (DOTs), while SPS sections 

were designed and constructed to answer specific research questions. The broad study categories are listed

in table 1. Nearly 800 LTPP test sections are in the GPS 

category, and more than 1,700 other test sections are in 

the SPS category. Full suites of data (such as distress, 

traffic, material sampling, and climatic data) have been 

collected for each of the test sections. Some data are 

collected centrally; others are collected by the States 

and Provinces.

Above: Construction of an 

Arizona SPS-1 site in 1993.

Right: Materials sampling 

and testing for quality

control during construction 

of the SPS-2 site in 

Washington State.

2

FIGURE 1. Distribution of LTPP pavement test sections.
3

Table 1. LTPP General and Specific Pavement Studies 

 General Pavement Studies (GPS) Specific Pavement Studies (SPS)

GPS-1 Asphalt Concrete on Granular Base SPS-1 Strategic Study of Structural Factors for 

Flexible Pavements 

GPS-2 Asphalt Concrete on Bound Base SPS-2 Strategic Study of Structural Factors for 

Rigid Pavements 

GPS-3 Jointed Plain Concrete Pavement SPS-3 Preventive Maintenance Effectiveness of 

Flexible Pavements 

GPS-4 Jointed Reinforced Concrete Pavement SPS-4 Preventive Maintenance Effectiveness 

of Rigid Pavements 

GPS-5 Continuously Reinforced Concrete Pavement SPS-5 Rehabilitation of Asphalt Concrete Pavements 

GPS-6 Asphalt Concrete Overlay of Asphalt Concrete Pavement SPS-6 Rehabilitation of Jointed Portland Cement 

Concrete Pavements 

GPS-7 Asphalt Concrete Overlay of Portland Cement Concrete SPS-7 Bonded Portland Cement Concrete Overlays 

on Concrete Pavements 

GPS-8 (discontinued) SPS-8 Study of Environmental Effects in the 

Absence of Heavy Loads 

GPS-9 Unbonded Portland Cement Concrete Overlays on SPS-9 Validation of Strategic Highway Research

Portland Cement Concrete Pavements Program Asphalt Specification and Mix Design 

(Superpave) 

National and Highway Agency Investment 

Establishing and operating a program of this magnitude requires significant resources, and the total Federal investment since 1987 exceeds $260 million.1

These funds have supported the wide array of LTPP 

activities, including test section construction and 

data collection; database development and maintenance; rigorous quality control/quality assurance

(QC/QA) programs; coordination through local, regional, and national meetings; and data analysis and 

product development.

State and Provincial highway agencies have supported the LTPP program by bearing most of the construction costs for the test sections, maintaining and allowing 

access to the sections, providing traffic control for field 

monitoring and materials testing, supplying monitored 

traffic loading and classification data, and serving on 

TRB’s LTPP Committee and its supporting expert task

groups. Many States have participated in pooled fund 

studies that have greatly extended the usefulness of the 

LTPP program.

Accomplishments and Benefits 

The LTPP program has generated a wide range of benefits across the pavement engineering and performance 

spectrum. Hundreds of applications have been identified that make use of LTPP data, and the utility of LTPP

data is increasing. A detailed listing of each report, procedure, and product utilizing LTPP information has been

compiled on the FHWA LTPP Web site at http://www.

fhwa.dot.gov/pavement/ltpp. A summary of available 

tools and resources for highway agency pavement engineers appears on the inside back cover of this report.

LTPP benefits and products fit broadly within three 

categories, which form the structure of this report: 

•	 The LTPP database—largest and most comprehensive in the world. 

•	 Advances in pavement performance measurement.

•	 Contributionsto pavement design and management.

Examples in each category are highlighted in the following sections to show how LTPP-related findings continue 

to benefit the pavement community and the driving 

public. 
4

Primary Data

The single most significant product of the LTPP program 

is the pavement database—the largest and most

comprehensive collection of research-quality

performance data on in-service highway 

pavements ever assembled. The database 

has supported national, State/Provincial, 

and local research projects, as well as a variety of international analysis efforts. With appropriate maintenance and update activities in 

place, the LTPP database will continue to be the primary source of information for future generations of 

pavement researchers. 

The LTPP database is composed of 21 modules containing data categories such as climate, materials testing, 

traffic volumes and loads, pavement layer types and 

thicknesses, material properties, and pavement condition (distress, longitudinal and transverse profile, and 

structural response). Each module contains a number of 

related tables. Within each table are data elements selected by their importance to pavement engineering applications. To help users navigate the millions of records 

stored in the database, the LTPP Table Navigator application was developed. 

Ancillary Data

The LTPP Ancillary Information Management System 

(AIMS) data contains supplementary information that 

complements the LTPP database. Examples of AIMS data 

include the following: 

•	 Time history files collected from falling-weight

deflectometers (FWDs). 

•	 Raw profile data.

•	 Scanned distress maps and photos.

•	 Traffic files from the central traffic database.

•	 Test section materials stored at the FHWA Materials

Reference Library in Nevada. 

Data Accessibility

The LTPP Customer Support Service Center provides free 

access to the latest pavement performance data and related data quality information through the Customer

Support Service Center’s annual standard data release 

on DVD in Microsoft Access format and the LTPP Products Web site (www.ltpp-products.com). Users typically 

are from State and Provincial highway agencies, local 

highway agencies, academia, and pavement engineering firms. Information in the LTPP database is readily 

available to support user requests.

Users can submit data requests for pavement performance data as well as data from the AIMS system through 

BENEFITS of the LTPP DATABASE 

“We see the LTPP database serving into the indefinite future as a key component 

of the agency’s pavement research activities, and those activities will benefit 

substantially from the many LTPP data collection and analysis activities in 

FY 2010–FY 2015 that are mentioned in the FHWA document.” 

Victor Mendez, Chairman 

Twenty-third letter report of the Transportation Research Board 

Long-Term Pavement Performance Committee, 

December 27, 2007

An updated, 

comprehensive LTPP 

Standard Data Release 

is distributed each year. 

Also available on DVD 

is the comprehensive 

LTPP Reference Library. 

The primary LTPP 

database is maintained 

at the Turner-Fairbank

Highway Research 

Center.
5

A Foundation for Advancement 

The LTPP database will continue to be the single largest benefit from the 

LTPP program, a legacy to future pavement researchers. Providing reliable pavement performance data to thousands of requestors throughout the academic community and the public and private sectors, the 

database has been the foundation for fundamental and applied research and the nucleus for advancements in pavement design and 

management processes. With continued support supplementing the 

quantity, quality, and accessibility of LTPP data, the LTPP database will be

the catalyst for pavement advancements over the foreseeable future. 

Future benefits will be achieved primarily through the exposure of 

engineers and researchers to the LTPP program and database. This effort is already underway, and many universities incorporate the LTPP 

database as part of undergraduate curriculums. Familiarity with the program will facilitate the implementation of LTPP products, and increased 

exposure to LTPP products will result in applications beyond those currently envisioned. 

LTPP’s Customer Support 

Service Center, which has 

filled more than 5,000 data 

requests since 1997. The

LTPP Products Web site has 

more than 3,000 registered 

users from 77 countries, and 

more than 45,000 requests

have been processed online. 

The more than 50,000 total 

requests for LTPP information are a testament to the 

program’s usefulness and its 

broad acceptance by the research community and State and Provincial partners. 

The LTPP database supports research and product development. By the end of 2009, more than 600 research 

documents that utilized LTPP data had been published.

Based on the steady growth in the number of publications with time, it is anticipated this number will increase 

significantly in the years ahead. The benefits this information has yielded are far-reaching, and those benefits and 

accomplishments are discussed in the following sections. 

Data Analysis Program 

Data analysis has been a critical component of LTPP from 

the program’s inception. Members of expert task groups

and other stakeholders have expended significant effort

over the years in optimizing data analysis activities. For

the past decade, the Strategic Plan for LTPP Data Analysis 

has guided the analysis efforts using LTPP program 

funds.2 Testing the quality and completeness of the LTPP

data has been a major activity under the program, which 

has funded many studies that provide a solid technical 

basis for understanding pavement performance. 3

Seasonal Monitoring Program 

Recognizing that weather and traffic loading are the two

major causes of pavement deterioration, LTPP made the 

collection of research-quality environmental data a top

priority. The Seasonal Monitoring Program (SMP) study 

was designed to measure the impact of daily and seasonal temperature and moisture changes on pavement 

structures and the response to loads. Sixty-four sites (see 

figure 2) were instrumented to collect climatic data and 

variations in parameters such as temperature and moisture content. Monitoring data were collected frequently,

in many cases monthly, so that, for example, pavement 

deflection data could be correlated to seasonal variations of material properties.

Direct measurements at SMP projects and automated 

weather station locations have provided designers and 

researchers with an abundance of high-quality data. The

further innovative step of developing virtual weather stations has already paid significant dividends, and all environmental data will support significant future savings.

Analysis using SMP data has been useful in evaluating 

seasonal load restrictions, defining moisture and frost 

penetration prediction models, and developing the 

LTPPBind software application that helps highway 

agencies select the most suitable and cost-effective 

SuperPave® asphalt binder performance grade for a particular site. The LTPP program has produced a set of three 

CD-ROMs that document the installation, monitoring, and 

decommissioning of SMP sites, as well as detailed information on the equipment and experimental design.

The climatic information available through the LTPP 

program has proved valuable in many areas. Of particular 

note is the LTPPBind software, which was developed to 

aid in the selection of performance-graded binders. This 

software was based on the original SHRPBind software 

LTPP DataPave and other 

LTPP products are available 

online at www.ltppproducts.com.
6

and incorporates LTPP’s revised temperature models. In 

many instances, the original SHRPBind models were 

found to be overly conservative, and implementation of 

LTPPBind has resulted in significant cost savings—an estimated $50 million per year. 

LTPP climatic information can be useful in other areas 

of research. One study used climatic data from the LTPP 

program to evaluate rigid pavement design procedures 

for airfields.4 The research investigated the estimation of 

critical design edge stress, effect of finite slab width and 

length, effect of a second subbase layer and stress adjustment factor required due to effective temperature

differential, thermal curling and moisture warping, fatigue versus thickness relationships, and alternative

structural deterioration relationships. 

Findings from the study were used to modify the fatigue curve used for airfield design. The new curve is 

more representative of actual critical edge stresses and 

can incorporate additional design features, such as various slab sizes, climatic effects, and multiple subbase layers, as well as innovative pavement configurations. The 

results from the study are currently being used to modify 

the stress analysis and thickness design program used

for rigid pavement design in airfield applications. 

LTPP and the Next Generation of 

Pavement Professionals 

Familiarizing users with the LTPP database is a major program accomplishment. LTPP data are used not only in 

pavement research at the State/Province and national levels, but also at local and county levels and internationally. 

Introducing LTPP data to analysts has long been a priority, 

particularly so at the university level. LTPP training has 

been given to interested professors, and several universities have introduced curriculums involving LTPP data. Using the LTPP database allows professors to create academic problems that relate to real conditions. Students learn to 

process the data, determine pavement condition, and recommend rehabilitation strategies. For graduate students 

in pavement engineering, using the pavement data is essential to investigating how pavement systems behave.

The American Society of Civil Engineers (ASCE) jointly 

with FHWA sponsors a competition to encourage use of 

LTPP data. The ASCE-LTPP International Contest on LTPP 

Data Analysis has been running since 1998 and has four 

entry categories: undergraduate students, graduate students, partnerships, and curriculum. (Contest information is available at www.fhwa.dot.gov/pavement/ltpp/

contest.cfm.) Student participation is ensuring that the 

next generation of pavement designers and researchers 

will be LTPP savvy—and spurs the development of new

products and practices.

 “...Kansas DOT uses LTPPBind software as 

an integral part of their pavement design 

process.” 

Lon Ingram 

Former Chief of Materials and Research, Kansas 

Department of Transportation 

“The best part of the database is that it 

allows students to ‘get their hands dirty’ 

with real data.”

Susan Tighe, Ph.D.

Professor of Engineering, University of Waterloo

FIGURE 2. Distribution of instrumented sites in

the LTPP Seasonal Monitoring Program.

An automated weather station at an SPS-8 site in Francis, Utah.
7

Through both design and necessity, the LTPP program 

has advanced pavement measurement and monitoring 

practices. In addition, bias and variability—which can

have large consequences on pavement treatment selection—can be thoroughly evaluated using the data collected by the LTPP program. The data collection techniques developed for the program have been fully

documented and have been implemented by highway 

agencies across North America, providing the highway 

community with better and more consistent data. Improved data collection practices have resulted in twofold 

savings—reducing both data collection costs and pavement rehabilitation or reconstruction life cycle costs. 

Pavement condition data that are of consistently high 

quality are extremely important in pavement evaluation,

design, and management to ensure that decision makers select the best possible alternatives and timing 

schedules for maintaining agency networks. Distress

data are also used in research studies, construction QC/

QA, and pavement failure investigations—all of which

demand quality data.

Based on its long history in managing LTPP activities, 

FHWA is uniquely qualified to assist agencies and industry with data collection issues. 

Field Data Collection 

The LTPP program has provided a wide variety of benefitsrelated to field data collection equipment and procedures. Numerous LTPP data collection procedures have 

been adopted by AASHTO and industry, with the most 

widely implemented being the Distress Identification 

Manual for the Long-Term Pavement Performance Program 

(DIM). In discussions of LTPP implementation, 90 percent 

of State highway agencies have indicated that LTPP data 

collection equipment or test methods have been used

by their organizations.

Distress Monitoring 

The LTPP program has developed the robust and 

thorough DIM that highway agencies can use to 

improve or standardize their condition data collection. Illinois and Mississippi have used the DIM 

as the basis for quantifying distress on projects

with pavement warranties. Additional benefit has 

been realized in other States, including Nevada

and Oklahoma, as they update and standardize

their condition data collection techniques for

pavement management purposes. Many local 

agencies also use the DIM, which enables them to collect 

data on local roads without spending valuable resources 

to develop their own collection systems. 

Distress Viewer and Analyzer (DiVA Online) is a software application that can overlay distress information for 

graphical analysis. Originally developed as a QA/QC review tool for LTPP distress data, DiVA islinked to the LTPP

distress survey maps, photographs, and digital images. 

The distress data can be displayed to show a time series/

time history of a pavement section under evaluation for 

trend analysis and variability bands for distress trends. 

DiVA can analyze several survey sections at the same

time. It provides reports in both graphical and exportable tabular formats. 

DiVA’s ability to graphically display distress data can 

assist highway agenciesin analyzing distressinformation

in several ways, for example: 

•	 Examining collected data prior to entry in a pavement management system. 

•	 Comparing survey results against previous surveys

and reviewing abnormalities.

•	 Evaluating trend discrepancies for possible explanations (e.g., differences in interpretation, maintenance 

or rehabilitation activities).

ADVANCES in PAVEMENT PERFORMANCE MEASUREMENT 

Distress Identification 

Manual, first issued in 

1987, now in its 4th 

edition. Available at 

http://www.tfhrc.gov/

pavement/ltpp/

reports/03031.
8

•	 Validating distress data for MEDPG calibration.

•	 Reviewing variability in distress data within pavement management systems, thus lessening the impact of variability.

Other recent publications include updated manuals for 

FWD measurements and for profile measurements and 

processing. These and other LTPP documents are available 

on the LTPP Web site or by contacting the LTPP Customer 

Support Service. 

Profile Monitoring

The LTPP program developed procedures for 

evaluating profiler equipment and comparing

the performance of various models against actual 

elevation measurements. The program also developed tools to monitor the consistency of measurements between different devices and wrote 

model procurement specifications. LTPP also developed a set of routine premeasurement equipment checks, calibration procedures, and qualitycontrol protocols. Ultimately, FHWA published 

the definitive work on the use of profiling technology:

Long-Term Pavement Performance Manual for Profile Measurements and Processing (FHWA-HRT-08-056, 2008). 

Traffic Monitoring

The LTPP program has made significant advances across 

the pavement engineering spectrum since its initiation 

in the late 1980s. It can be argued that the program’s single 

greatest impact in pavement 

performance monitoring to 

date is in the area of collecting 

data on traffic volumes and 

loads. While the technologies for 

collecting automated vehicle 

classification (AVC) and weighin-motion (WIM) data were commercially available when 

the LTPP program began, their implementation was varied, and there were no standardsfor data quality, analysis,

or interpretation. 

In the program’s early years, significant unknowns

related to AVC and WIM data collection included the accuracy and reliability of the wide range of available 

equipment—both portable and permanent. Since then,

the LTPP program has been instrumental in advancing 

the technology of AVC and WIM data collection. Several 

States, including Washington, Arizona, and Texas, have

used LTPP test sections as a means to incorporate automated data collection into their standard operations. 

The LTPP program has developed standards and 

products to address variability in the data collected from 

the various AVC/WIM technologies: 

•	 Equipment calibration protocols.

•	 Smoothness specifications for the pavement in the

vicinity of the monitoring equipment, along with an

associated software application—the WIM Smoothness Index Software—to help optimize WIM equipment locations. 

•	 Software that imports data records and provides both

quality control checks and computed parameters.

Based on LTPP work, Smoothness of Weigh-in-Motion Systems (AASHTO provisional specification MP 14-05) was developed to assess the smoothness of pavement approaches at WIM sites. There are both long and short wavelength 

pavement contributions to vehicle dynamics, and this 

specification helps agencies to determine whether the 

pavement smoothness at existing locations will introduce 

significant errors in the resulting WIM data, as well as to 

identify the optimal location for new WIM installations. 

Considering the importance of the SPS projects—

with multiple sections at the same location to allow 

comparison of various design features and rehabilitation 

“It is important to note that the obtained data had previously been checked for 

accuracy and summarized into the Microsoft Access format. If this had not been the 

case, extensive time would have been required to manually process and edit the 

large amount of traffic data.” 

M.S. Buchanan, Ph.D.

Traffic Load Spectra Development for the 2002 AASHTO Design Guide 

Truck approaching

a WIM installation in 

Arkansas.

Operational procedures for measuring 

longitudinal pavement 

profiles. Available at 

http://www.fhwa.dot.

gov/pavement/ltpp/

pubs/08056.
9

strategies—the SPS Traffic Data Collection Pooled Fund

Study was established to install, calibrate, and validate 

continuous traffic data. The study guidelines require a

site to have data that pass the LTPP quality control standards for at least 210 days a year, including field validations. Highway agencies have contributed more than 

$2.7 million to this effort, and the LTPP program has significantly improved the availability and quality of monitored traffic data as a result. 

Quality Control/Quality Assurance

QC/QA have been integral components of the LTPP program since its inception. Quality control plans are in 

place for every field data element, and while processes 

are in place for office processing software and detailed 

QC checks in the LTPP database, the LTPP program has

long recognized that collecting high-quality data expedites subsequent data processing activities. Many of the

LTPP products, such as the DIM and the FWD calibration 

centers, are the direct results of the program’s emphasis 

on QC/QA. In 2001, when the Office of Management and 

Budget issued government-wide guidelines regarding 

data quality standards, the LTPP program already had

policies in place that ensured compliance. 

FWD Calibration Centers 

Reliable and precise measurements of pavement strength 

enable pavement engineers to design and schedule appropriate repairs at cost-effective intervals. Errors in FWD 

data lead to errors in pavement analysis. Securing accurate data depends on the periodic calibration of these 

complex hydraulic-electrical-mechanical devices.

In the early days of the LTPP program, calibration procedures and regional calibration centers were identified 

as priority needs. The original FWD calibration protocol 

was finalized in 1992, and calibration centers were established in Pennsylvania, Texas, Minnesota, and Nevada 

(the Nevada center was eventually moved to Colorado). 

These centers provided calibration services not only for 

LTPP FWDs, but also for FWD equipment owned by highway agencies and consultants. In the first 3 years of center operations, many of the non-LTPP FWD units were 

found to be significantly out of calibration. The LTPP calibration centers thus provided an essential public service 

that resulted in significant construction savings. These 

savings were most notable in situations where design is 

driven by FWD measurements, such as in flexible pavement overlay designs and jointed rigid pavement loadtransfer rehabilitation designs. 

With advances in technology, FHWA recognized the

need to update the FWD calibration system and initiated 

a pooled fund study, Falling-Weight Deflectometer Calibration Center and Operational Improvements (TPF 

5(039)), for that purpose. The study resulted in a new 

calibration system that takes advantage of improvements in technology; an updated FWD calibration protocol: AASHTO Standard Practice R 32-09: Calibrating the 

Load Cell and Deflection Sensors for a Falling Weight Deflectometer; and arrangements for ongoing support of 

the calibration centers, ensuring that they will remain 

available to the pavement community. 

Left: Calibrating an FWD. The reference load cell is positioned under the FWD load plate.

Right: The LTPP program periodically updates its data collection guidelines for use of FWD equipment (available at http://www.

fhwa.dot.gov/pavement/ltpp/pubs/06132).
10

The upgraded hardware and software in the new 

system allow calibration to be completed in about 

2 hours, about a third of the time previously required.

The system is compatible with all brands of FWDs available in the United States. Changes in the new system 

include the use of an accelerometer for deflection sensor 

calibration, the ability to calibrate all deflection sensors 

simultaneously by using a multiple sensor stand, use of 

a Windows-based programming language that can 

read native data formats from each brand of FWD, and 

use of modern data acquisition techniquesto eliminate

sensitivity problems. 

Extensive research has established that the new procedure is as accurate and repeatable as the old one. All 

State DOT–operated calibration centers have implemented the procedure, as have three manufacturer-run 

centers in the United States and Europe.

To encourage State highway agencies and other 

FWD users to use the calibration facilities, FHWA has produced a video, “Calibrating the Falling Weight Deflectometer,” which can be viewed at www.fhwa.dot.

gov/multimedia/research/infrastructure/calibration. 

Also available on CD, the video illustrates the new calibration procedure, explains how to prepare for a successful calibration, describes how calibration improves 

the quality of backcalculated data, and explains the

impact of proper calibration on overlay design.

The LTPP program also developed a maintenance 

manual that provides instructions on reconditioning an 

FWD: The Long-Term Pavement Performance Program Falling Weight Deflectometer Maintenance Manual. Addressed 

to FWD owners, operators, and technicians, the manual 

describes the process of disassembling and reassembling 

the components and subcomponents of an FWD to extend its service life. 

Since 1997, more than 500 FWD and heavy-weight 

deflectometer calibrations have taken place at the FWD

calibration centers. The centers provide an important 

service to the highway community, particularly when 

FWD-derived inputs are used for rehabilitation design. 

With support services from the AASHTO Materials Reference Laboratory, the centers continue to serve public 

and private agencies.

Data Variability 

An important element to consider in pavement management systems and many research applications is the 

variability associated with a data point. LTPP data has 

been analyzed to develop typical variability ranges for

manual distress surveys5, 6, 7

 and longitudinal profiles.8

Pennsylvania used LTPP data to verify its own acceptance limits for pavement distress data.9

 Variability associated with data collection equipment has also been

studied, particularly in longitudinal profile where three 

different makes of high-speed profilers have been used

over the years. An in-depth analysis comparing profiles 

by equipment type, completed in 2005, determined that

changesin profiler equipment did not impact the overall

variability in LTPP smoothness data.10

Objective Comparisons Between 

Geographic Locations 

Researchers must determine how much confidence to 

assign information obtained from different sources, 

particularly if those sources are from different parts of 

North America, where collection and testing procedures 

can vary. The LTPP program has established strict guidelines for data collection and processing that require

State-Operated FWD Calibration Center Contacts 

California

Lorina Popescu, University of CaliforniaBerkeley Pavement Research Center

510-665-3663; lpopescu@berkeley.edu

Colorado

Paul J. Smith, Colorado Department 

of Transportation

303-398-6547; 

paul.j.smith@dot.state.co.us

Minnesota

Tim Andersen, Minnesota Department 

of Transportation

651-366-5455; timothy.lee.andersen@

state.mn.us

Montana

John Amestoy, Montana Department 

of Transportation

406-444-7651; Jamestoy@mt.gov

Pennsylvania

Cal Heinl, Pennsylvania Department 

of Transportation

717-783-4824; cheinl@state.pa.us

Texas

John Ragsdale, Texas Transportation 

Institute

979-845-9921; j-ragsdale@tamu.edu
11

A dynamic modulus testing 

apparatus (courtesy North 

Carolina State University).

Innovations and New Products 

In both the field and lab, LTPP measurement innovations and related products are benefiting the pavement 

community. Direct measurements at SMP projects and automated weather station locations have provided 

designers and researchers with an abundance of high-quality environmental data. The further step of developing virtual weather stations has already paid significant dividends (an estimated $50 million per year for 

LTPPBind alone), and all environmental data will support significant future savings. 

Improving material characterizations for bound and unbound layers is critical for advancing mechanisticbased designs. The LTPP program has provided many advances across this spectrum—from establishing

testing protocols and increasing uniformity between testing labsto providing quality data sets used in analysis activities.

Tools such as LTPP WIM Cost Online and the LTPP WIM Smoothness Index software provide agencies with 

the means to optimize their entire traffic data collection program—and further guidelines on calibrating and

validating equipment allow loading and classification information to be utilized with confidence. Anecdotally,

Arizona hasreported saving $2 million in construction costs on a single project by utilizing the LTPPWIM data.

specific equipment, accredited distress raters, standardized processing software, and thorough QC/QA practices that enable analysts to utilize data from sections

around the country without introducing additional 

sources of uncertainty. 

Laboratory Testing 

The ability to accurately and consistently quantify material properties is an important step in pavement selection, design, and construction. The LTPP program has 

made significant contributionsin characterizing material

properties by improving test protocols, as well as in providing a database of properties that are linked to actual

field performance—both of which have furthered the

development and use of mechanistic approaches in 

pavement engineering. 

Resilient Modulus Testing of Bound and 

Unbound Layers 

When establishing characteristics in the unbound layers

—including subgrade, subbase, and base materials—

resilient modulus is the property most relevant to pavement design. It is no surprise that establishing granularlayer resilient modulus values has been a priority activity 

for the LTPP program. In the program’s early days, researchers, observing that samples from the same location 

yielded wide variations in test results regardless of which 

lab was used, recognized that there was no

concise test protocol for resilient modulus testing. 

LTPP made a considerable investment in establishing Test Protocol P46—Resilient Modulus

of Unbound Materials.11 This protocol has been 

widely adopted, a process that was accelerated 

first by a series of videos directed to administrators, engineers, and lab managers and technicians, followed by a CD-ROM containing both 

the videos and documentation for the LTPP 

Guide for Determining Design Resilient Modulus 

Values for Unbound Materials.12 The LTPP program also adopted a highly repeatable test protocol to determine asphalt resilient modulus: 

Protocol P07.13 

Equipment Startup Procedures 

For both bound and unbound resilient modulus testing, 

a key element for ensuring uniformity is the LTPP startup

procedure. The LTPP resilient modulus CD-ROM contains 

a 15-minute video describing the startup and quality

control processes. The startup procedures were developed specific to the resilient modulus protocols, but 

could broadly be applied to setting up closed-loop, servohydraulic testing equipment. This procedure has been

adopted by equipment manufacturers as a quality control check during equipment production.
12

An original LTPP objective was to acquire data for use in

evaluating existing design methods and in developing 

new ones. The program has achieved this objective. 

LTPP data have been used in numerous studies tasked

with evaluating or developing design procedures, the 

most recent being the Mechanistic-Empirical Pavement 

Design Guide (MEPDG). The LTPP program has also supported the implementation of, and advancements in, 

pavement management systems for agencies throughout the country. 

The Mechanistic-Empirical Pavement 

Design Guide 

Since the late 1990s, one of the pavement research community’s single largest investments has been in the 

development of the MEPDG. Development of the new 

guide required detailed information about pavements

located across the country and representing a wide 

range of loading, climate, and subgrade conditions with 

varying structural compositions. The LTPP database was 

critical to the development of the MEPDG, as it is the 

only source of comprehensive pavement data representative of national conditions. In fact, the MEPDG could 

not have been completed without the type and national 

extent of data provided by the LTPP studies. All of the 

traffic loading defaults provided in the MEPDG, for example, were derived from the LTPP traffic database using 

WIM sites across the United States and Canada, and all of 

the distress and smoothness models in the MEPDG were 

calibrated using LTPP data.

The MEPDG models evaluate the impact of traffic, climate, materials, and subgrade stiffness on performance 

and account for the interactions among these components. The MEPDG predicts individual performance 

measures (i.e., transverse cracking, fatigue, smoothness,

rutting) based on site condition input for a given trial 

pavement section. These prediction techniques can be

used in pavement evaluation studies, as well as in forensic investigations. 

MEDPG Development 

National Cooperative Highway Research Program 

(NCHRP) Project 1-37A (Development of the 2002 

Guide for the Design of New and Rehabilitated Pavement Structures: Phase II) was undertaken to develop a

new pavement design guide based on mechanisticempirical relationships and utilizing accepted and proven

technologies. The new guide was developed to address 

the many limitations of the existing design procedure, 

which was based on data collected at the American 

Association of State Highway Officials (AASHO) Road 

Test in Illinois in the late 1950s. That design procedure has 

served the industry well, but has deficiencies due to 

some of the limitations of the AASHO Road Test: 

•	 Today’s traffic loads are much higher than they were

six decades ago. 

“The AASHTO MEPDG is based on engineering mechanics principles as 

much as possible. However, the heart of the design procedure is key

distress and smoothness prediction models that required calibration

with measured performance data. The LTPP database provided such 

long-term performance data for hundreds of asphalt, concrete, and 

rehabilitated pavement sections that were used in the national calibration. Without LTPP data for the national calibration, the MEPDG distress 

models could not have been validated for use throughout the country. 

In addition, LTPP data is invaluable to each State highway agency for its 

own local validation and calibration purposes.” 

M. I. Darter, Ph.D.

Applied Research Associates, Inc. 

CONTRIBUTIONS to PAVEMENT DESIGN and MANAGEMENT 
13

•	 Rehabilitated pavements were not monitored.

•	 Only one climatic condition and one subgrade type

were included in the road test. 

•	 Only one hot-mix asphalt and one PCC mixture were

studied. 

•	 Test pavements did not include drainage.

•	 Only 2 years of monitoring were conducted, rather

than the entire pavement life of every section (some 

sections did, however, fail within 2 years). 

Local Calibration 

The LTPP database is serving as a critical tool in implementing the new design guide. The MEPDG was delivered with the prediction models calibrated to average 

national conditions. For the guide to be an effective resource for individual agencies, the national models need 

to be evaluated against local and regional performance. 

The results of these evaluations are being used to determine if local calibration isrequired. In addition, LTPP sites

provide typical values for many of the MEPDG inputs. 

Additional studies have been initiated as a direct result of the MEPDG. NCHRP 1-40A (Independent Review 

of the Recommended Mechanistic-Empirical Design 

Guide and Software) investigated the assumptions, evaluated the reasonableness and reliability, and assessed 

the implementation opportunities of the new design 

procedure. 

The objectives of the NCHRP 1-40B project (Local 

Calibration Guidance for the Recommended Guide for 

Mechanistic-Empirical Design of New and Rehabilitated 

Pavement Structures) were to develop a user guide and 

a manual on local calibration of the MEPDG. Local validation and calibration will rely heavily on the LTPP database 

as many agencies do not otherwise have the data necessary to complete this endeavor. 

Sensitivity Studies of Models 

Data from the LTPP SPS-5 project in New Jersey have 

been used to study the sensitivity of the MEPDG to 

weather and traffic inputs.14 The initial analysis compared 

the predicted outputs of the Enhanced Integrated Climatic Model for Pavement Design and found that the 

predicted moisture content for unbound material and 

temperature profiles of bound layers were significantly 

different from those measured on the SPS-5 project. 

LTPP and the Texas Flexible Pavement Database

Pavement data from the LTPP program were essential to the development of the MEPDG. Now those same data are proving critical to the development of local and regional pavement design models. Calibrated for 

national standards, the MEPDG models cannot be assumed to apply to 

specific locales—researchers have noted that in some cases the software

produces unreasonable results, partly due to regional differences in soil, 

construction materials and practices, climate, and traffic loads. 

Recognizing the need for data that can be used to develop, validate,

and calibrate flexible pavement design models, the Texas DOT (TxDOT) 

recently sponsored a 3-year project at the University of Texas at Austin to 

develop and deploy a flexible pavement database, with two objectives: 

•	 To build a reference database comprising design, construction, structural, and performance data for selected flexible pavement sections in 

Texas. 

•	 To develop guidelines for local calibration of the MEPDG.

A major challenge for the project researchers was to design a database of 

sufficient size and complexity to fulfill pavement design needs—yet not

so large or complex as to be too burdensome to maintain. 

The project resulted in the online Texas Flexible Pavements Database 

with pavement sections spanning the climate, traffic, and structure types 

found in Texas. LTPP data were critical to the development of the database, 

providing the long-term performance data necessary for initial calibration. 

Of the 86 pavement sections housed, 45 are LTPP sections in Texas. Each 

has information on traffic, materials, structure, and performance history. 

The other 41 sections are relatively new sections recommended by TxDOT. 

When sufficient performance data have been collected on the newer sections, they will become the primary data source for validation and calibration of pavement design and performance models.

“The database is delivering what it was designed for. There is no doubt 

that the interim calibration factors recommended by this study are more 

accurate for predicting pavement performance in Texas than the default 

national values,” says Jorge Prozzi, the principal investigator. “The database will evolve over time. We recommend that Texas continue to monitor these sections annually for at least the next 10 years, and add new 

sections as newer materials like recycled asphalt and warm-mix asphalt

come into wider use in the State. New sections with thin asphalt surfaces 

and surface treatments should also be added.”

The procedures followed and the calibration factors determined in the 

calibration methodologies—one for calibration of mechanistic rutting

models and the second for empirical roughness models—are available in

the project’s final report, Development of the Texas Flexible Pavements Database, available at www.utexas.edu/research/ctr/pdf_reports/0_5513_2.pdf.
14

These differences prompted additional research on the 

sensitivity of the MEPDG performance predictions using 

climatic inputs from different weather stations. 

This study stands as a testament to the critical role 

LTPP data will play in evaluating, calibrating, and validating the MEPDG on a local level. The results indicate that 

the MEPDG will need to be refined for use in New Jersey’s conditions, and the refinement process will likely

rely heavily on LTPP data. 

Other studies are being performed in support of the 

MEPDG at the State and national levels. One example is 

NCHRP 1-42A (Modelsfor PredictingTop-Down Cracking

of Hot-Mix Asphalt Layers), which is investigating models 

to predict top-down cracking, a damage function included in the MEPDG as a placeholder for this observed 

but not fully understood distress. The LTPP SPS-1 projects 

will serve as an excellent resource for studying the effect 

of pavement thicknessin the development of top-down

versus bottom-up cracking. Forensic analysis of the

SPS-1 projects can provide valuable information on the 

factors influencing the origins of top-down cracking.

Evaluation and Modification of 

Design Methods 

Understanding how design methods relate to actual 

performance is extremely valuable. Design procedures 

can be modified based on research findings, and better 

decisions on design policy can be made. 

AASHTO Rigid Pavement Design Spreadsheet 

A study was undertaken to make improvements to the

1993 AASHTO Rigid Pavement Design Guide. The improvements included enhanced k-value selection techniques, curling and warping considerations, guidance

on joint spacing, inclusion of slab/base friction, and new 

performance prediction capabilities. 

These advancements led to more cost-effective and 

reliable pavement designs. The research utilized LTPP

data to conduct the most critical portion of the study—

validation of the new methodologies. Based on the findings, AASHTOadopted the new techniques as part of the

1998 Supplement to the AASHTO Guide for Design of 

Pavement Structures. 

In addition, the LTPP program sponsored the development of a software application to automate the new 

and improved design process. Not only does the software incorporate all of the new features of the Rigid 

Pavement Design Guide, it can also perform sensitivity 

analyses. This capability has contributed to improved 

pavement designs as engineers have better information 

regarding the effects of variability in design inputs. The 

software has been Web-enabled—LTPP Pavement Online—and is available through the LTPP Products Online

Web site, free of charge (see figure 3).

Continuously Reinforced Concrete Pavement 

Performance Study 

The LTPP GPS-5 experiment provides performance, design, climatic, and traffic information for 85 continuously 

FIGURE 3. Screen capture 

of LTPP Pavement Online—

Rigid Pavement Design 

software. 
15

reinforced concrete pavement (CRCP) test sections located in 29 States across the country.15 This information 

was used to study CRCP performance and to identify the 

characteristics of sections that are performing well. 

Using the September 1999 LTPP database, inventory and performance information was used to evaluate CRCP test sections. High-severity transverse cracking, average crack spacing, total punchouts and

patches (i.e., localized failures), and smoothness were

of particular interest to the researchers. This information was beneficial in evaluating current CRCP design 

practices as well as understanding key design factors

in performance. 

Further analysis was conducted to evaluate the characteristics of the GPS-5 test sections that were performing extremely well. Pavements that were 20 or more 

years old and that exhibited an International Roughness 

Index measurement of less than 1.5 m/km, no localized

failures, and no high-severity transverse cracks were defined as excellent performers. Of the 85 GPS-5 test sections, 13 fell into this category. 

The results from this study are useful to pavement designers, materials engineers, and others who make the

critical choices that will determine level of service and return on investment when building CRCP pavements. The 

data available through LTPP will continue to provide a 

means of evaluating pavement performance to enhance 

design, construction, and maintenance activities. These 

analyses will lead to improved performance at reduced 

overall cost. 

Improved Predictive Capabilities 

Using the models developed as part of pooled fund 

study TPF-5(013), Effect of Multiple Freeze–Thaw Versus

Deep Frost Penetration on Pavement Performance (Final 

Report, FHWA-HRT-06-121), a software application, LTPP 

Performance Forecast Online, was developed that provides pavement performance predictions (i.e., smoothness and distress) for both flexible and rigid pavements. 

Each of the models provided in the Performance Forecast application incorporated data from LTPP test sections and is completely described and documented in 

the report. The predictions/forecasts are based on userdefined inputs for environment, traffic, structure, and 

subgrade conditions.

The online application (www.ltpp-products.com/

Predictor/index.aspx) can be used by State, county, and 

local highway agencies to forecast or estimate performance trends for pavement sections within their jurisdictions. These estimates are useful in evaluating the 

prediction capabilities of the MEPDG to determine 

whether local calibration is necessary for the validation 

and implementation process. The predictions are also 

beneficial in updating pavement family performance 

curves within pavement management systems, allowing 

decision makers to optimize investment choices and

improve overall pavement network conditions.

Understanding Factors That Contribute to 

Pavement Performance 

Traffic loading and environmental conditions are the 

two major causes of pavement deterioration. Therefore, 

accurately capturing both elements—as done in the

LTPP program—is paramount in analyzing pavement

performance. Other critical elements in pavement performance include the materials used in the bound and 

unbound layers, as well as the selection and timing of 

preventive maintenance activities. 

Pavement engineers consider many alternatives 

when designing a pavement system. The LTPP database 

has been used to sort out these alternatives and establish optimal design features for use in certain situations. 

The data has also been used to change design policy at 

State and local agencies. 

An extensive study, LTPP Data Analysis: Influence of 

Design and Construction Features on the Response 

and Performance of New Flexible and Rigid Pavements, 

was conducted under NCHRP16 on all SPS-1, SPS-2, and 

SPS-8 projects to evaluate the influence of site condi-

“Indeed, LTPP is providing one of the most important elements in 

technology development through field validation and calibration. 

The use of LTPP data helps demonstrate to the user community that 

the models and technologies being developed really match realworld problems.” 

M. W. Witczak, Ph.D.

Professor of Civil Engineering, Arizona State University 
16

tions and design factors on pavement response and 

performance. SPS-1 projects consist of multiple flexible 

pavement test sections constructed consecutively with 

various layer thicknesses, base types, base thicknesses,

and drainage configurations. Similarly, test sections on 

an SPS-2 project are composed of various slab thicknesses of the PCC, base type, PCC flexural strength, 

drainage, and lane width combinations. Both of these 

projects provide an excellent source of data to evaluate 

the effectiveness of various design features and the impact of in situ conditions. The SPS-8 experiment was 

designed to study the influence of environment in the 

absence of heavy loading. 

This study can be used by those interested in the 

contribution of design factors on flexible and rigid 

pavement performance. The present benefit of this 

study is an understanding of the interaction between 

design parameters and climate and the resultant 

changes in pavement performance. The LTPP database 

provides a means of conducting this type of study on a 

national scale. The findings from this study can be used 

to optimize cost-effective design alternatives and will

be useful in transferring mechanistic evaluations to 

field performance for various design parameters. 

Maintenance and 

Rehabilitation Insights 

Before the LTPP program, there was limited information 

on the performance of rehabilitation and maintenance 

activities. The experimental design of the LTPP database 

ensured that information on maintenance and rehabilitation strategies and their deterioration rates was collected (SPS-3 and SPS-4 maintenance studies; SPS-5 and 

SPS-6 rehabilitation projects; GPS-6 and GPS-7 asphalt 

concrete overlay sections). Thus the database provides 

performance data for various maintenance and rehabilitation alternatives. 

Some of the LTPP experiments offer side-by-side comparisons of treatment alternatives that allow direct comparison while keeping selected factors (such as subgrade,

traffic, and climate) constant. The results can be used to 

determine the most cost-effective treatments based on 

life cycle cost analysis. These experiments can also be used 

to predict the expected service life of treatments based on 

in situ conditions. By knowing the expected life,pavement

management engineers can develop proper timing intervals and determine budgetary needs. 

As part of the LTPP data analysis program, an NCHRP 

study, LTPP Data Analysis: Effectiveness of Maintenance 

and Rehabilitation Options,17 evaluated the performance of various maintenance and rehabilitation strategies on immediate improvements in pavement condition, as well as their long-term effects. In addition, the 

impact of climate, traffic, and pre-treatment pavement 

condition were analyzed. For flexible pavements, both

maintenance and rehabilitation strategies were studied; for rigid pavements, only rehabilitation strategies 

were considered. Data from LTPP SPS-3, SPS-5, SPS-6, 

GPS-6B, and GPS-7B experiments were utilized in the

NCHRP study. The findings from this study can be used 

to understand the impact of maintenance and rehabiliAbove: A pavement test section with a 2-in. recycled 

asphalt overlay.

Left: LTPP rehabilitation experiments included jointed 

concrete pavements.

LTPP experiments have 

contributed to more costeffective pavement preservation 

strategies. 
17

tation treatments. With this understanding, engineers 

can make informed decisions on treatment types

based on the existing condition of the pavement, expected traffic, and climate. Findings such as these are 

very useful to pavement decision makers in evaluating

the cost effectiveness of alternative strategies, materials, and methods. 

Use of Reclaimed Asphalt Pavement

The growing demand for materials to rehabilitate the 

highway infrastructure in the United States and the increasing need for sustainable and environment-friendly 

alternatives have substantially increased the demand for 

recycling materials. The most common application of material recycling in pavements is RAP, reclaimed asphalt 

pavement. 

Research was done under LTPP SPS-5 to determine 

the effects of design and construction features on pavement response and performance and to establish their 

importance in predicting the future performance of rehabilitated pavements. The performance data from LTPP 

SPS-5 revealed that RAP and virgin hot-mix asphalt mixes 

used in overlays of flexible pavements show approximately the same performance across a wide range of 

climates, traffic, and existing pavement conditions over a 

service life ranging up to 17 years.18 The evaluation of the 

deflection data suggested that when thick overlays are

designed for pavement sections, the likelihood that the

performance will be similar for both types of mixes increases. This major finding should give agencies confidence in specifying RAP mixtures for overlays when economic and other conditions warrant. 

Materials Reference Library

From the onset of the LTPP program under 

SHRP, administrators planned to store test 

site materials to make them available for

future research. As such, the Materials Reference Library (MRL) was established, initially in Austin, Texas. Now located in Reno, 

Nevada, the MRL stores more than 1,000 

tons of pavement materials—portland cement, asphalt cement, natural aggregates, and combinations of these materials—in both loose and core

forms. Collected from across North America, the samples represent a wide variety of physical, chemical, and 

geologic properties and field performance histories. Although most of the materials are from LTPP projects, 

there are also materials from WesTrack and a few other federally funded research activities. The MRL also

houses film and distress maps produced during the collection and interpretation of automated surface distress data collection on LTPP sites. 

The MRL continues to grow. A significant re-sampling effort was recently completed on the SPS projects 

to ensure that sufficient material is available to the pavement community. In addition, recycled asphalt and 

warm-mix asphalt samples are being collected and stored at the MRL as the Asphalt Research Consortium, 

under a cooperative agreement with FHWA, constructs pavement test sections using those materials. 

The MRL will enable future analysts to compare new test methods to actual performance using materials 

from LTPP projects. It will provide a critical link between field performance and material properties for new

test methods and will support a variety of other materials-related research efforts.

The inventory of MRL 

materials is available 

at www.ncenet.com/

ltpp/mrl. The facility 

has shipped more than 

17,000 lb of material to 

pavement researchers 

in seven countries. 
18

Other aspects of the LTPP program can be defined 

monetarily as cost savings recognized through implementation and can serve as a basis for determining the 

return on investment of the LTPP program. 

LTPP by the Numbers 

The numerous innovations that have directly resulted 

from the LTPP program—procedures, software tools,

manuals, and research findings—have been implemented across the United States and abroad. A partial listing 

of LTPP resource statistics is shown in table 2. 

Opportunity Cost 

From an agency perspective, cost savings do not contribute directly to an increased bottom line, but rather to 

an optimized opportunity cost. Almost invariably there

are significantly more projects to be completed than 

funding will allow. Funds that do not have to be used on 

one project can thus be shifted to another. As an example, the design of a project in Arizona was being based

on existing tables of equivalent single-axle loads. However, because of the presence of an LTPP WIM site, measured traffic data were available. These data clearly 

showed traffic loads to be much less than the design table indicated. This resulted in a cost savings of more than 

$2 million for the project—extra funds that could then

be allocated to other priority projects. Nationwide, these 

“save/extra” moneys serve to improve the overall pavement network without incurring additional costs.

RETURN on INVESTMENT 

Colorado Implements Proven PCC Pavement Practices 

The Colorado Department of Transportation (DOT) has been a strong supporter of LTPP by being proactive in examining performance at its LTPP 

test sections and making improvements based on these evaluations. A

2006 report19 documented the implementation of improved PCC pavement practices based on LTPP test sections. The LTPP data confirmed that 

widening a slab from 12 ft to 14 ft (3.7 m to 4.3 m) provides the structural 

equivalent of increasing slab thickness by 1 in. (2.5 cm); and that a single

1/8-in. (0.32-cm) cut is as effective as Colorado DOT’s previous standard 

3/8-in. (0.95-cm) double cut for PCC joints, thereby providing a savings of 

$0.57 per linear foot of joint ($1.87/m). These results were derived from the 

SPS-2 and SPS-4 projects, respectively. 

Many aspects of the LTPP program that are clearly beneficial to the highway community are difficult to quantify

monetarily—such as procedures for QC/QA for researchlevel data collection, data collection techniques and

practices, test methods, and database management. 

Other programs are benefiting from the extensive experience of the LTPP program, as well. For example, plans 

for the Long-Term Bridge Performance Program emphasized lessons learned in LTPP: the importance of standardizing data collection procedures and documenting

data cleaning and analysis in rigorous reports. The plan 

also recommended using the LTPP program as a model 

for organization structure and oversight.20 

“The true benefit of the LTPP database will come from its use in developing new 

pavement designs and methods for building and maintaining pavements.” 

Preserving and Maximizing the Utility of the Pavement Performance Database,

Transportation Research Board, 2009 
19

Table 3. Estimated Annual Expenditures for Highways and Roads in 2006 Dollars 

Under SAFETEA-LU1

Expenditures (billions)

 Type of Expenditure Federal State and Local Total

Capital $34.0 $40.6 $74.6

Operation and maintenance $1.2 $58.5 $59.7

1

Safe Accountable Flexible Efficient Transportation Equity Act: A Legacy for Users, Public Law 109-59.

Table 2. Long-Term Pavement Performance (LTPP) Resources 

 LTPP Resource Statistics 

Requests for data 50,000+ requests filled

LTPP Products Web site 3,000+ registered users (in 77 countries)

Published documents resulting from LTPP data 	 500+ publications

American Society for Civil Engineers/LTPP 60 entries

International Contest on LTPP Data Analysis

Distress manuals 20+ State agencies use in operations

Falling-weight deflectometer calibration centers 	 500+ calibrations performed

Weigh-in-motion systems 550+ installations

SPS Traffic Data Collection Pooled Fund Study 28 Specific Pavement Study sites 

Materials Reference Library materials 2,000,000 lb available for future research 

Materials Reference Library shipments 17,000 lb delivered for other research

Projected Cost/Benefit Ratios 

In 2007, the Congressional Budget Office published a 

paper documenting “Trends in Public Spending on 

Transportation and Water Infrastructure, 1956 to 2004.” 21

This report provides public expenditures (on the Federal, State, and local levels) for both capital spending and 

operation and maintenance spending, and it also breaks

these expenditures down by type of infrastructure, including highways and roads. Annual expenditures under current legislation22 are provided in table 3. Using 

numbers from the 2007 report as a base and subtracting the amount spent on bridges, one can extrapolate 

that more than $114 billion is spent each year on roadways and highways. Typically 40 percent of that amount 

is dedicated to pavement construction and maintenance; thus the annual investment in pavements totals 

about $45.6 billion. 

Quantification of the return on research investments 

can prove quite challenging. In most instances, the

Better estimates of traffic volumes and loads support more rational allocations of 

construction and rehabilitation dollars.
20

Table 4. Projected Savings as LTPP Data Are Utilized 

Projected Future Savings (2015–2024)*

Annual Cumulative

No additional Continued No additional Continued 

 Savings to Date monitoring monitoring monitoring monitoring

$1.7 billion $228 million $456 million $2.28 billion $4.56 billion

*Assumes that future annual pavement costs remain steady at $45.6 billion/year. 

research does not include a discussion of cost implications, and assumptions must be made. This scenario 

utilizes cost information whenever possible and is very

conservative in assessing the benefit. Simply providing 

a cumulative savings is not realistic since independent 

findings do not necessarily provide a 1:1 cumulative relationship. For instance, it is not practical to suggest 

that 10 separate findings, each resulting in “saving” a 

single half inch in a pavement design, would cumulatively provide 5 inches of savings. 

Suppose the return on investment (savings) from 

the LTPP data since program inception in 1989 is onequarter of 1 percent (0.0025), or $1.7 billion. As LTPP

monitoring is continued past 2009, the annual savings, 

beginning in 2015, is expected to be about $456 million per year, or about 1 percent of the total pavement 

investment—double what could be expected if monitoring ended today (table 4). Over a 10-year span (2015 

to 2024), the savings achieved as a result of continued 

monitoring will total $4.56 billion. 

To reiterate, the estimated savings shown are extremely conservative. Considering that the MEPDG 

team estimates $1 billion in annual savings from implementing the new design procedure, and—as demonstrated herein—that LTPP’s benefits range much more

broadly than supporting development and implementation of the MEPDG, it could be argued that future LTPP 

cost savings should start at 10 figures. 

By any measure, the LTPP program has already provided a substantial return on investment, with a benefit–

cost ratio exceeding 6:1. Put in the context of other large 

research programs, this number is quite reasonable. For

instance, the estimated return on research investment for 

MnROAD is 8.9:1,23 and Washington DOT has documented returns on its State research funds at over 18:1 when 

considering all funding sources in the State.24 In fact, the 

benefit–cost ratio for LTPP over the 2015–2024 period is 

projected at over 50:1, using recent AASHTO and TRB estimates for proposed levels of funding support. Furthermore, even greater returns can be achieved through expanding future monitoring activities to pavement 

materials and design methods that have been developed 

since 1987. 
21

A Critical Role 

There is no doubt that the LTPP database has played a critical role in the 

development and evaluation of every major pavement design methodology developed over the past 20 years. These include the 1993 and 

1998 AASHTO design procedures, Superpave, and—most recently—

the MEPDG, which the developers indicate will generate annual savings 

of $1 billion. Calibrated nationally with LTPP sections, the MEPDG has 

shown significant reductions in the initial cost for heavily trafficked

pavement designs. Beyond overall design procedures, the LTPP data has 

supported and will continue to support model development and validation for a wide array of performance predictors and indicators. 

The LTPP program has generated savings across a wide range of 

pavement management activities—from improving data collection

equipment and operations and establishing data variability and reliability

toproviding quality data setstobe used forbaseline comparisons against

agency data. As one example of potential savings, the Indiana DOT has 

estimated that a 1-mil (0.0254 mm) error in FWD calibration will result in 

additional costs of $17,900 per lane-mile ($11,187 per lane-kilometer).25

Looking to the future, the largest component of highway pavement

programs and budgetsislikely to involve rehabilitating and maintaining

existing pavements, rather than new construction. The LTPP program 

has many rehabilitated test sections that were monitored for several 

years before rehabilitation and have continued to provide service since 

rehabilitation. Capturing the full performance life of these projects will 

require continuing monitoring into the future if the benefit of future

savings based on lessons learned is to be realized.

Furthermore, considering that the SPS-1 and SPS-2 experiments are 

most relevant to establishing the influence of specific design features 

on pavement performance, and many of these projects are not close to 

the end of their design lives, determining the influence of specific design features requires continued monitoring. Data exist to support early

conclusions, but additional information is necessary to learn the true 

impacts of these features over a section’s entire design life. 

The key drivers for establishing the LTPP program still exist today, more than 20 years after the initiation of test 

section monitoring. High-value sections remain in the 

program, and there is much to be gained by continuing 

to monitor them. There is a rich base of information still 

to be harvested from LTPP studies that will aid in improving the performance of pavements. The LTPP program 

will provide benefits and deliver accomplishments for 

the foreseeable future. 

As such, TRB published a report in 2009 titled Preserving and Maximizing the Utility of the Pavement Performance Database.26 This document recommends a multiyear strategy designed to leverage LTPP’s strengths to 

deliver high-priority results. On a similar track, AASHTO

has formally endorsed the LTPP program and publicly 

championed for enhanced funding. 

In support of these endorsements, FHWA has issued a 

policy document, LTPP Beyond FY 2009, What Needs to Be 

Done,27 which describes the activities to be undertaken

by the program to reap additional returns on the Nation’s 

significant investment in LTPP. This document provides a 

framework of work to be done during the 2010–2015

time period and outlines the additional benefits that will 

accrue from these actions. 

The LTPP program is an ongoing and active program. 

Looking forward, there are literally thousands of additional potential benefits LTPP can provide. The overarching benefits are increased service life for all types of pavements, lowered life cycle costs, and improved safety. 

Following are a few of the specific ways in which the 

LTPP program will contribute to improving pavement 

programs across the country: 

•	 Optimizing treatment selection.

•	 Assessing the impact of the environment on performance. 

THE ROAD AHEAD
22

•	 Providing baseline data sets for agencies to evaluate

performance internally. 

•	 Allowing year-to-year checks against agency pavement management system/pavement condition index data. 

•	 Calibrating new field data equipment.

•	 Comparing the performance of new materials with

conventional materials. 

•	 Evaluating the performance effects of specific design

features. 

•	 Allowing local calibration and model refinement for

the MEPDG.

The benefits and accomplishments of LTPP to date, as 

discussed in this document, have already provided a 

significant return on investment to the Nation. In the 

future, the LTPP program will yield additional information of tremendous value to pavement engineers and 

managers, who will translate this information into strategies and procedures for building better, safer, more 

cost-efficient roads for the Nation. 

“LTPP is a major contributor toward assuring that we will have good pavements 

into the 21st century.” 

Charlie Churilla

“An Investment in the Future” 

Roads & Bridges, August 2001 
23

1. Preserving and Maximizing the Utility of the Pavement Performance 

Database, by the Long-Term Pavement Performance Committee, 

Transportation Research Board, Washington, DC, 2009, p. 6.

2. See http://www.fhwa.dot.gov/pavement/ltpp/stratplan/strategic.cfm.

3. Key Findings from LTPP Analysis 1990–1999 (FHWA-RD-00-085), 2000, 

http://www.fhwa.dot.gov/pavement/pub_details.cfm?id=274, and Key 

Findings from LTPP Analysis 2000–2003 (FHWA-RD-04-032), http://www.

fhwa.dot.gov/pavement/pub_details.cfm?id=213, 2004, Federal 

Highway Administration, Washington, DC.

4. “Effects of Various Design Features on Rigid Airfield Pavement Design,” 

Y-H Lee and S-T Yen, in Proceedings of the 27th International Air Transport 

Conference (CD), American Society of Civil Engineers, Washington, DC, 

2002.

5. “Assessing Variability of Surface Distress Surveys in Canadian Long-Term 

Pavement Performance Program,” Stephen N. Goodman, Transportation 

Research Record: Journal of the Transportation Research Board, Vol. 1764, 

2001, pp. 112–18. 

6. Study of LTPP Distress Data Variability, Volume I, Research Report, Long-Term 

Pavement Performance Program (FHWA-RD-99-074), G. R. Rada, C. L. Wu, 

R. K. Bhandari, A. R. Shekharan, G. E. Elkins, and J. S. Miller, Law PCS/

Federal Highway Administration, Washington, DC, 1999.

7. “‘Off-The-Wall’ Pavement Distress Variability Study,” J. F. Daleiden and 

A. L. Simpson, Transportation Research Record No. 1643, Pavement 

Management and Monitoring of Traffic and Pavements, 1998, pp. 621–70. 

8. “Profile Data Variability in Pavement Management: Findings and Tools 

from LTPP,” Hao Yin, Shelley M Stoffels, and Charles A. Antle, in Proceedings 

of the 2006 Airfield and Highway Pavement Specialty Conference, American 

Society of Civil Engineers, Reston, VA, 2006.

9. “Use of LTPP Data to Verify the Acceptance Limits Developed for 

PennDOT Pavement Distress Data,” V. P. K. Ganesan, S. M. Stoffels, 

J. Arellano, and D. Morian, in Improving Pavements With Long-Term 

Pavement Performance: Products for Today and Tomorrow (FHWAHRT-06-109), Federal Highway Administration, 2006.

10. “Quantification of Smoothness Index Differences Related to Long-Term 

Pavement Performance Equipment Type,”R. W. Perera and S. D. Kohn,

Soil and Material Engineers, Inc./Federal Highway Administration, 

Washington, DC, 2005.

11. Long Term Pavement Performance Project Laboratory Materials Testing 

and Handling Guide: Protocol P46, Resilient Modulus of Unbound Granular Base/Subbase Materials and Subgrade Soils, August 1996, www.tfhrc.

gov/pavement/ltpp/pdf/p46.pdf.

12. See http://www.fhwa.dot.gov/pavement/ltpp/rmodulus.cfm for 

information on obtaining these products.

13. Protocol P07. Test Method for Modulus and Strength Tensile Test Device, 

Version 1.1, August 2001, www.tfhrc.gov/pavement/ltpp/pdf/

ProtocolP07.pdf.

ENDNOTES

14. “Investigations of Environmental and Traffic Impacts on ‘MechanisticEmpirical Pavement Design Guide’ Predictions,” Sameh Zaghloul, Amr 

Ayed, Amir Abd El Halim, Nicholas P Vitillo, and Robert W. Sauber, 

Transportation Research Record: Journal of the Transportation Research 

Board No. 1967, Transportation Research Board, Washington, DC, 2006.

15. “Performance of Continuously Reinforced Concrete Pavements in 

the LTPP Program,” S. D. Tayabji, C. L. Wu, and M. Plei, Proceedings of the 

Seventh International Conference on Concrete Pavements, International 

Society for Concrete Pavements, 2001, www.concretepavements.org. 

16. “LTPP Data Analysis: Influence of Design and Construction Features on 

the Response and Performance of New Flexible and Rigid Pavements,” 

K. Chatti, N. Buch, S. W. Haider, A. S. Pulipaka, R. W. Lyles, D. Gilliland, and

P. Desaraju, prepared for National Cooperative Highway Research 

Program, June 2005, http://trb.org/publications/nchrp/nchrp_w74.pdf.

17. NCHRP 20-50(3&4). Final Report, LTPP Data Analysis: Effectiveness of 

Maintenance and Rehabilitation Options, June 2002, http://gulliver.trb.org/

publications/nchrp/nchrp_w47.pdf.

18. “Lessons Learned from the Long-Term Pavement Performance Program 

and Several Recycled Sections in Texas,” by Dar-Hao Chen, in Roadway 

Pavement Preservation (Transportation Research E-Circular, Issue No. 

E-C078) Transportation Research Board, Washington, DC, 2005, pp. 

70–84, http://onlinepubs.trb.org/onlinepubs/circulars/ec078.pdf.

19. Implementation of Proven PCC Practices in Colorado, A. Ardani, Report 

CDOT-DTD-R-2006-9, Colorado Department of Transportation, Denver, 

CO, 2006.

20. Development of a Comprehensive Plan for a Long-Term Bridge Performance 

Program: Final Report for DTFH60-05-RA-00105, Michael J. Chajes, Sue 

McNeil, Harry W. Shenton III, Dennis R. Mertz, Nii Attoh-Okine, Diane S.

Kukich, and Melissa R. Williams, August 24, 2006, www.ce.udel.edu/cibe/

projects/LTBPP%20Final%20Report.pdf.

21. Available at http://www.cbo.gov/ftpdocs/85xx/doc8517/08-08-

Infrastructure.pdf.

22. http://www.fhwa.dot.gov/safetealu/index.htm.

23. “Economic Benefits Resulting from Road Research Performed at 

MnROAD,” Benjamin J. Worel, Maureen Jensen, and Timothy R. Clyne, 

presented at the Third International Conference on Accelerated 

Pavement Testing, October 2008, Madrid, Spain, p. 12. 

24.	http://www.wsdot.wa.gov/biz/mats/pavement/Pavement%20

Research%20Benefits.pdf.

25. NCHRP Synthesis 381: Falling Weight Deflectometer Usage, A Synthesis of 

Highway Practice, National Cooperative Highway Research Program, 

Transportation Research Board, Washington, DC, 2009, p. 12.

26. Available at http://www.trb.org/Publications/Blurbs/Preserving_and_

Maximizing_the_Utility_of_the_Pavem_160696.aspx.

27. Report No. FHWA-HRT-09-052, available at www.fhwa.dot.gov/

pavement/pub_details.cfm?id=651.
24

Accessing LTPP Information and Products 

Accomplishments and Benefits Database: This document highlights the accomplishments and benefits of the LTPP program over the first 20 years of data collection. 

During development of this report, an extensive database of existing LTPP reports, 

products, and research results was compiled. The LTPP Literature Database can be 

accessed here: http://ltpp.org/user_corner.shtml.

FHWA LTPP Web Site: FHWA maintains an LTPP Web site to disseminate information 

resulting from the LTPP program. www.fhwa.dot.gov/Pavement/ltpp

LTPP Customer Support Service Center: LTPP data requests, technical questions, and

data user feedback can be submitted to the LTPP Customer Support Service Center

via email at LTPPinfo@dot.gov or by calling 202-493-3035. 

LTPP Products Web Site: Many of the products mentioned in this document can be 

found online at the LTPP products Web site, which also contains online access to the 

LTPP database. www.ltpp-products.com 

Materials Reference Library: More than 1,000 tons of sample materials are held 

at this site for research purposes. Included are pavement cores, asphalt cement, portland cement, aggregates, and other materials. www.ncenet.com/ltpp/mrl

Strategic Plan for LTPP Data Analysis: Since 1999, analysis of the LTPP data at the 

national level has been guided by the Strategic Plan for Data Analysis. The Strategic 

Plan was developed by the TRB Expert Task Group on LTPP Data Analysis, recommended by the TRB LTPP Committee, and adopted by FHWA as the basis for selecting 

LTPP analysis projects and evaluating progress in LTPP data analysis. www.fhwa.dot.

gov/pavement/ltpp/stratplan/strategic.cfm 

ASCE-LTPP International Contest on LTPP Data Analysis: The contest is designed to 

encourage university students, professors, and highway department engineers from 

around the world to get involved in using the LTPP database. www.fhwa.dot.gov/

pavement/ltpp/contest.cfm 

SPS Traffic Data Collection Pooled Fund Study: This study includes two phases. 

Phase I consists of assessing, evaluating, and calibrating the current weigh-in-motion 

and vehicle classification systems used to collect traffic data at SPS sites across the 

country. Phase II consists of installing and maintaining new weigh-in-motion equipment as necessary to ensure high-quality data collection. More information is available at www.fhwa.dot.gov/pavement/ltpp/spstraffic/index.cfm.
25
26

Publication No.

FHWA-HRT-10-071

HRDI-13/08-10(1M)E

Research, Development, and Technology

Turner-Fairbank Highway Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

Visit us on the Web at www.fhwa.dot.gov/pavement/ltpp.

Recycled

Recyclable