Pilot
Projects Kick Off Traffic Data Pooled-Fund Study
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: larry.wiser@fhwa.dot.gov),
or visit the LTPP Web site at http://www.fhwa.dot.gov/pavement/ltpp/spstraffic/.
