Long-Term Pavement Performance Program Highlights: Accomplishments and Benefits 1989-2009

BACKGROUND

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 cost-effective 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 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.

FIGURE 1. Distribution of LTPP pavement test sections.

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 https://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.
• Contributions to 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.

Table 1. LTPP General and Specific Pavement Studies

FHWA-HRT-10-071