Publication Number: FHWA-RD-00-063
Date: November 2000

LTPP Program Launches Traffic Data Pooled-Fund Study

To increase and improve the collection of monitored traffic data for five of the long-term pavement performance (LTPP) program Specific Pavement Study (SPS) projects, the Federal Highway Administration (FHWA) has initiated a new State pooled-fund study. The study is the result of a 1998 review of the LTPP data, which concluded that the spatial distribution, timeliness, quantity, and quality of the monitored traffic data needed to be improved to ensure the success of the SPS -1, -2, -5, -6, and -8 experiments.

The SPS experiments were designed to learn how such factors as cumulative traffic loading affect pavements of different compositions, environmental conditions, and layer thicknesses. However, it is estimated that at least half of the SPS -1, -2, -5, -6, and -8 sites do not have the quantity and quality of traffic data that is needed for analysis.

Following the 1998 review, the Transportation Research Board (TRB) - LTPP Committee and the American Association of State Highway and Transportation Officials Task Force on SHRP Implementation recommended a pooled-fund study as a way of filling in the gaps. The total cost of implementing the study through FY 2003 is estimated at $10 million. While the study is targeted to those States with SPS sites, participation by other States is encouraged, given that all States will benefit from the increased understanding of pavement performance that the SPS experiments will provide. To date, 18 of the 37 States with SPS experiments have expressed interest in joining the pooled-fund study, while 12 have indicated that they prefer to meet their data collection commitment individually.

FHWA plans to kick off the study by conducting site visits to all SPS projects to evaluate the site, perform a baseline test of the pavement smoothness, and check the calibration of the site's weigh-in-motion (WIM) sensors. The quality of data obtained from WIM sensors, which collect information on such factors as vehicle and axle weights, is highly dependent upon the pavement in which they are installed. Smoother pavements provide more accurate and less variable measurements. Once the site visits have been completed, a report will be prepared, providing a baseline for future data analysis and site evaluations.

A set of protocols has been developed for use nationally for verification of scale performance; pavement smoothness requirements; model WIM system specifications, including accuracy requirements and construction guidelines; and data collection processing. These are available on the Web at https://www.fhwa.dot.gov/pavement/ltpp/spstraffic/. FHWA's LTPP team plans to conduct a series of pilot projects to validate the protocols and train highway personnel in annual WIM evaluation activities.

Highway agencies that are interested in participating in the pooled-fund study or who want more information should contact Larry Wiser at FHWA, 202-493-3079 (fax: 202-493-3161; email: larry.wiser@fhwa.dot.gov).

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