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45
Similar summaries are prepared by the county, district, and for
the entire state. If the acceptable rate for any of the pavement
condition indicators differs more than 2% (routes MD47N
and MD49E in the example) from the previous year, the
record is highlighted for further investigation.
Data Quality Investigation A data quality investigation is
required for those sections in which the trend analysis indi-
cates a potential data quality problem. This investigation aims
to identify the reason for the suspicious rate change, determine
if there was a problem, and, if there is one, find a solution to
fix it or to prevent it from happening again. Historic treatment a
information, test and equipment event records, pavement
images, and weather conditions during testing are collected
and analyzed to determine which factors may have contributed
to the suspicious condition variation. If test operation or equip-
ment condition is identified as a concern, a notice is sent to the
data collection staff requesting that the data be re-collected or
suggesting modifications to the data collection procedures.
Data Collection Equipment Comparison
After replacing its automated data collection equipment,
MDSHA conducted a data comparison study to evaluate the b
consistency of the data collected between the old and new
FIGURE 20 VDOT yearly pavement condition
devices. The two systems were used to collect data on a comparisons (96): (a) Pavement Condition Index;
250-mile loop. The smoothness (IRI), cracking, and rutting (b) Smoothness (IRI, in./mi).
values for a sample of one hundred 0.1-mile segments were
compared. The comparison showed that the two systems pro-
duced similar IRI data, but statistically different rutting and shows the comparison for the overall PCI and IRI for 1996
cracking measurements. Cracking data were collected from and 1997 after removing all sections that received preserva-
pavement images using a proprietary automated cracking tion treatments. The PCI plot pointed out a deficiency in the
detection software tool. rating procedure used in 1997, which overestimated the PCI
for the pavements in poor condition. The IRI plot also sug-
To resolve the cracking data consistency problem, MDSHA gests a problem, because the smoothness was lower in 1997
initiated a study to compare the results of the two systems with than in 1996; this was attributed to the switch from ultrasonic
reference ratings determined visually from the same pictures sensors to laser sensors.
collected with the data collection systems for the same 100 seg-
ments. This ground truth determination is critical for hardware The network-level comparison prompted a review of the
and software calibration to improve data accuracy. pavement data collection approach, which helped enhance
data quality requirements in successive years and establish
formal quality assurance/quality control processes. Most sig-
VIRGINIA
nificantly, VDOT defined the following vision statement for
VDOT has used different pavement distress data collection data collection "to collect pavement condition data with suf-
methodologies over the past 15 years. These changes have ficient detail and accuracy to model deterioration and per-
resulted in a continuous improvement process through which form multiyear planning with the PMS. Data variability for
the department has gained significant experience and devel- each data element must be smaller than the year-to-year change
oped sophisticated quality control and assurance procedures. in that element."
VDOT collects data over 0.1-mile- (161-m)-long manage-
ment units. The study also prompted the agency to require the cali-
bration of smoothness measuring equipment against a ref-
erence device and its verification against VDOT equip-
Background ment, and pilot testing of a sub-network during the data
collection contract inception phase. It also provided the
Larson et al. (96) presents some interesting approaches for data that was used to develop precision (±12%) and bias
comparing time-history pavement condition data. Figure 20 (±5%) criteria for the PCI.
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46
Current Data Collection Practice conditions. Data collected by VDOT were used as reference
values. The sites were used to establish the service provider's
In 2005, after a formal solicitation process, VDOT contracted precision and bias, which in turn were compared with the
with a service provider to collect, process, and deliver network- ones required in the RFP.
level pavement condition data (51). The equipment specified
included digital pavement imaging to a resolution of at least For calibration of the pavement distress measurements,
2 mm, laser measurements of longitudinal and transverse the service provider used an automated crack detection rating
profiles, and automated or semi-automated distress quantifi- process and semi-automated ratings of the additional dis-
cation. The potential service providers were required to pro- tresses. The reference distress surveys were conducted by
vide documentation of their quality control plans for all aspects VDOT staff and the independent third party using the equip-
of the project, ranging from equipment calibration through ment collected images. This effort also served to train all dis-
data delivery. The selected service provider had an estab- tress raters, unify criteria, and made the necessary adjust-
lished quality control plan, but added an outside third party ments to the process. Comparisons were made based on the
to provide an independent verification and validation of the overall pavement condition index; the allowable difference
data before delivery to VDOT for this project. The service was ±10 points.
provider-supplied quality process flow diagram (Figure 21)
outlined the flow of data collection, data processing, quality
control, independent validation and verification, and data Independent Verification and Validation
acceptance processes.
The verification and validation of the pavement distress
data by an independent quality auditor was performed after
Initial Calibration the service provider had completed all in-house quality
control reviews and believed the data were ready for sub-
The calibration of the service provider's longitudinal pro- mittal to VDOT. Acceptance criteria require that 95% of the
file, transverse profile, and pavement distress measurement data checked fall within plus or minus 10 index points of
processes was done using 13 known-location control sections. the third-party data. The third party evaluated a 10% ran-
The control sites varied in length, smoothness, and distress dom sample of the pavement deliverables. This process
Production Data
Data Processing
Collection
Control Site - Semi-Auto
Start up Process - Verification Sites
Adequate - Automatic Internal QA
- Control Sites - Image Quality
(VDOT) - QA
- Field QC
- SOP
NO
NO
Deliverables Deliverables Deliverables
- Data - QC Report - QA Report
`
- Report
- Documents
NO NO
Independent Validation Deliver to VDOT
&Verification - Deliverable Files via Batch PMS Database
- 5% Data Review Pass ftp site Acceptance AMS Database
- Data Completeness IV&V - Images via portable (VDOT) Video Database
- Index Limits hard drive
Deliverables Deliverables
- IV&V Report - QA IV&V Report
- Deliverable Table s - 0.1 mi Delivery Table
- Homogeneous
sections delivery
table
FIGURE 21 VDOT quality process flow diagram [after Shekharan et al. (51)].
