Publication Number: FHWA-HRT-11-009
Date: December 2010

The LTPP Program: Two Decades of Advancements in Pavement Design and Management

More than 20 years after data collection began for the Long-Term Pavement Performance (LTPP) program, the benefits and products generated by the program continue to change pavement design and management worldwide, resulting in better, longer lasting, and more cost-effective roadways and an improved driving experience. These advancements are detailed in a new Federal Highway Administration (FHWA) report, Long-Term Pavement Performance Program: Accomplishments and Benefits 1989-2009 (Pub. No. FHWA-HRT-10-071).

Launched in 1987 as part of the Strategic Highway Research Program (SHRP), the LTPP program continued under the leadership of FHWA after SHRP ended in 1992, with transportation agencies in all 50 States, Puerto Rico, the District of Columbia, and 10 Canadian Provinces participating. The program has monitored the performance of nearly 2,500 in-service pavement test sections throughout the United States and Canada, including 801 test sections that are still being monitored today. The test sections represent a range of climatic and soil conditions.

"By following these pavements over time, researchers have gained insight into how and why they perform as they do, providing valuable lessons on how to extend the life of pavements," said Larry Wiser of FHWA. The data collected now forms the largest and most comprehensive pavement database in the world. This data has been translated into an array of products and tools for pavement engineers. It is also supporting research projects both in the United States and worldwide. By the end of 2009, more than 600 research papers and other documents using LTPP data had been published. "With appropriate maintenance and updates, the LTPP database will continue to be the primary source of information for future generations of pavement researchers," said Wiser. A new LTPP Literature Database available at http://ltpp.org/user_corner.shtml details the many reports, procedures, and products that have used LTPP data since the program began.

LTPP data was integral to the development of the American Association of State Highway and Transportation Officials' (AASHTO) Mechanistic-Empirical Pavement Design Guide (MEPDG). "The LTPP database provided long-term performance data for hundreds of asphalt, concrete, and rehabilitated pavement sections that were used in the national calibration for the MEPDG," said M.I. Darter of Applied Research Associates, Inc. "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 local validation and calibration purposes."

LTPP data has played a critical role, for example, in the design of the Texas Department of Transportation's Texas Flexible Pavements Database. The database is being used to develop guidelines for local calibration of the MEPDG. To learn more, visit www.utexas.edu/research/ctr/pdf_reports/0_5513_2.pdf.

A falling weight deflectometer (FWD) is calibrated. The reference load cell is positioned under the FWD load plate.

The experience gained through the LTPP program has advanced data collection procedures nationwide. 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). First issued in 1987, the DIM is now in its fourth edition. States such as Illinois and Mississippi have used the manual to quantify distress on projects with pavement warranties, while Nevada and Oklahoma have used it as they update and standardize their condition data collection techniques for pavement management purposes. Many local agencies also use the DIM.

The LTPP program has also had a significant impact on equipment calibration, recognizing the importance of calibration to collecting high-quality data and performing quality control and assurance. As a result of the LTPP program's advances, FHWA initiated a pooled fund study, Falling Weight Deflectometer Calibration Center and Operational Improvements (Study No. TPF-5 (039)). The study produced a new calibration system that takes advantage of improvements in technology and an updated FWD calibration protocol (AASHTO Standard Practice R 32-09: Calibrating the Load Cell and Deflection Sensors for a Falling Weight Deflectometer). The study also resulted in ongoing support for six regional FWD calibration centers established by the LTPP program, which are available for use by the entire pavement community. For more information on the regional calibration centers, visit www.fhwa.dot.gov/pavement/ltpp/fwdcont.cfm.

Also taking a leap forward under the LTPP program has been traffic data collection. The Specific Pavement Study (SPS) Traffic Data Collection Pooled Fund Study (Study No. TPF-5 (004)) has assessed, evaluated, and calibrated weigh-in-motion (WIM) systems at select LTPP SPS sites across the country. As part of the study, new WIM equipment was installed and maintained to ensure high-quality data collection. An LTPP Classification Scheme to categorize vehicle types at WIM locations was also developed as part of this study to standardize the classification scheme used at LTPP sites. This scheme is currently being verified and further enhanced under an LTPP data analysis project.

LTPP products developed to address traffic data collection include equipment calibration protocols and smoothness specifications for the pavement located near the monitoring equipment. Also available is the WIM Smoothness Index Software, which helps optimize the selection of locations for WIM equipment. For more information, visit www.fhwa.dot.gov/pavement/ltpp/spstraffic/index.cfm.

Pavement researchers worldwide, meanwhile, have benefited from the LTPP program's Materials Reference Library (MRL). Initially established in Austin, Texas, and now located in Reno, Nevada, the MRL stores more than 907 metric tons (1,000 tons) of pavement materials, including portland cement, asphalt cement, natural aggregates, and combinations of these materials. The materials have been shipped to pavement researchers in seven countries to date. To view the inventory of materials available, visit www.ncenet.com/ltpp/mrl.

Pavement researchers worldwide have benefited from the LTPP program's Materials Reference Library, located in Reno, NV. The library stores more than 907 metric tons (1,000 tons) of pavement materials.

A truck approaches a weigh-in-motion installation in Arkansas.

Many State and local transportation agencies use the data collection procedures contained in the Distress Identification Manual for the Long-Term Pavement Performance Program.

LTPP data are not only being used today but will benefit the next generation of pavement professionals tomorrow. Several universities have introduced curriculums that include LTPP data, for example. Using the LTPP database allows professors to create academic problems that relate to real pavement conditions. Students learn to process data, determine pavement condition, and recommend rehabilitation strategies. "The foundation is being laid for advancement as universities train future pavement engineers," says Wiser. To encourage use of the LTPP data, FHWA and the American Society of Civil Engineers sponsor an International Contest on LTPP Data Analysis. The contest includes categories for both undergraduate and graduate students, partnerships, and curriculum. To learn more, visit www.fhwa.dot.gov/pavement/ltpp/contest.cfm.

Looking ahead, the LTPP program continues its data collection and analysis activities, with many benefits still to come. An FHWA report, LTPP Beyond FY 2009, What Needs to Be Done (Pub. No. FHWA-HRT-09-052), describes the activities that can be undertaken to reap additional returns on the Nation's investment in the program, such as efforts to optimize pavement treatment selection, assess the impact of the environment on pavement performance, and compare the performance of new materials to conventional materials. To view the report, visit www.fhwa.dot.gov/pavement/pub_details.cfm?id=651.

The LTPP program's pavement performance data are available on DVD through the LTPP Customer Support Service Center or online at the LTPP Products Web site (www.ltpp-products.com). Long-Term Pavement Performance Program: Accomplishments and Benefits 1989-2009 (Pub. No. FHWA-HRT-10- 071) and an accompanying summary report (Pub. No. FHWA-HRT-10-072) are also available through the Customer Support Service Center at 202-493-3035 (email: ltppinfo@dot.gov). For more information about the LTPP program, visit www.fhwa.dot.gov/Pavement/ltpp, or contact Larry Wiser at FHWA, 202-493-3079 (email: larry.wiser@fhwa.dot.gov).

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