U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
|Accelerating Infrastructure Innovations|
Publication Number: FHWA-RD-02-008
Date: March 2002
Moving forward with its traffic data State pooled-fund study, the Long-Term Pavement Performance (LTPP) program conducted five pilot studies in the summer and fall of 2001. The pilot projects focused on finalizing the pooled-fund study's technical requirements for field performance evaluation and installation activities and validating a set of protocols developed by the LTPP program.
The study is designed as a mechanism for highway agencies to improve the collection of monitored traffic data for five of the LTPP Specific Pavement Study (SPS) experiments. A 1998 review of the LTPP data concluded that the spatial distribution, timeliness, quantity, and quality of the monitored traffic data must be improved to ensure the success of the SPS-1, -2, -5, -6, and -8 experiments. It is estimated that at least half of these SPS sites do not have the quantity and quality of traffic data that is needed for analysis. Twenty-two of the 37 States with SPS-1, -2, -5, -6, and -8 sites have expressed interest in participating in the pooled-fund study. Use of 100 percent State Planning and Research funds for all of the study's activities has been authorized to promote participation by every highway agency.
The study protocols cover verification of scale performance; pavement smoothness requirements; model weigh-in-motion (WIM) system specifications, including accuracy requirements and construction guidelines; and data collection processing. The WIM system specifications are particularly important, as these sensors collect information on such factors as vehicle and axle weights. The quality of the WIM data is highly dependent upon the pavement in which the system is installed, as smoother pavements provide more accurate and less variable measurements. For highway agencies seeking to install WIM systems using the pooled-fund mechanism, it is key to have a smooth, durable, and well-maintained pavement in place before the WIM system is introduced. It is important that States proceed now with constructing new pavement or rehabilitating existing pavement for the new WIM installations, as 5 years of data must be collected by 2009 for the study. This pavement construction is eligible to be covered by the pooled funds.
The five pilot studies, held in Arizona, Florida, Maryland, Michigan, and Texas, "were successful in demonstrating that the protocols were essentially correct as written," says Larry Wiser of the Federal Highway Administration (FHWA). The protocols' equipment performance specifications were shown to be achievable with current practice and technology and the recommended field practices, including speeds, temperatures, and vehicle condition, were validated. It was noted, however, that the smoothness specification was too restrictive for actual field conditions and it is now being revised. Study participants also noted that having well-trained drivers is essential to collecting quality data, as drivers of the test vehicles must travel at a constant target speed over the sensors and release their brakes when they are being weighed on the static scales. Also essential is having experienced traffic control workers on site during the data collection operations.
With the pilot field work concluded, the LTPP program will soon be issuing a request for proposals for a contractor to implement the pooled-fund study. Only these sites that have been assessed and shown to meet the performance requirements, regardless of which WIM is used, will be included in the LTPP analysis.
For more information on the pooled-fund study, contact Larry Wiser at FHWA, 202-493-3079 (fax: 202-493-3161; email: firstname.lastname@example.org), or visit the LTPP Web site at https://www.fhwa.dot.gov/pavement/ltpp/spstraffic/.