Since its beginning in 1987 as a Strategic Highway Research Program (SHRP) project, the Federal Highway Administration’s (FHWA) Long-Term Pavement Performance (LTPP) program has worked to improve the condition of the nation’s highway transportation system. Today, new initiatives continue to advance the goal of building more cost-effective and better-performing pavements.
The Falling Weight Deflectometer (FWD) Calibration Center and Operational Improvements pooled-fund study is designed to address issues related to aging equipment at the four LTPP regional FWD calibration centers. These centers were set up to assist states in properly calibrating FWDs so that pavement measurements taken as part of highway monitoring activities are accurate. Fifteen states are participating in the pooled-fund study, with $615,000 pledged to date. The study’s primary objectives include modernizing hardware and software used in the FWD calibration process, streamlining the calibration process and developing long-term technical support mechanisms for existing and future calibration centers. Cornell University is performing the work under a contract awarded in September 2004.
A new calibration process and related software is expected to be ready in April 2006, with training and installation at FWD centers to take place this summer. In addition to the four current SHRP/LTPP FWD centers, new centers are expected to open, including at least one in California. The installation and training for the four SHRP/LTPP FWD calibration centers is covered under the base period of the contract with Cornell University. Installation, training and technical support for additional calibration centers will depend on future contributions to the pooled-fund study. For more information on the study, visit www.pooledfund.org (search for study number TPF-5).
Another new LTPP initiative addresses the use of weigh-in-motion (WIM) equipment to collect traffic data, such as vehicle and axle weights, vehicle classification and speed. The smoothness of the pavement surface where WIM equipment is installed is important in achieving high-quality data, as smoother pavements reduce the amount of suspension/pavement dynamics, allowing the WIM system to perform better estimates of static wheel loads. The LTPP program, working with the University of Michigan Transportation Research Institute, has developed a smoothness index profile that allows a state to evaluate WIM sites.
The specification requires field collection of profile information for the candidate WIM site. Software developed by the LTPP program is then used to calculate the pavement surface roughness and determine if it meets acceptable index levels. This software is now available on CD. The specification has been tested in real-world conditions at field evaluations of WIM equipment sites under the LTPP Specific Pavement Study Traffic Data Collection pooled-fund study (Study No. TPF-5).
Later this year, under a similar initiative through the LTPP program, FHWA will be proposing another provisional specification to AASHTO via the Standing Committee on Materials. This related specification covers formal procedures to calibrate a WIM site for traffic data collection.