United States Department of Transportation
i
Development of a statewide online system for traffic data quality control and sharing.
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2009-12-01
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[PDF-1.50 MB]
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Edition:Final research report.
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Abstract:The Washington State Department of Transportation (WSDOT) operates thousands of Inductive Loop
Detectors (ILDs) on the freeways and highways of Washington State. The collection and disbursement of
this data is handled at the regional level, which has led to formatting differences and data fragmentation.
The Datamart Project is intended to consolidate data from all regions and store it in one location easily
searchable and accessible by all authorized users. Therefore a database and a web site have been created
in a computer application called Datamart to accomplish these tasks and demonstrate the idea.
Additionally, this research project has been also tasked with creating software applications for traffic
sensor data acquisition and developing error detection and correction methodologies for data quality
control. Error detection is accomplished in a three-step test proposed by this study to identify loop
detectors suffering from severe errors. The default conditions used by this test approach are general
enough to be applied in other states. Meanwhile, the approach also has its flexibility to use site specific
parameters to optimize its performance at a specific location. These severe errors identifiable by this
approach include wrong mode setting, cross chatting, extreme under sensitivity, and incorrect sensitivity
level, among others. Loop detectors suffering from incorrect sensitivity levels may be adjusted by the
proposed correction methodology. The correction methodology is designed to identify the true length of
the loop detector’s detection zone. Properly calibrated ILDs are generally assumed to have detection zone
sizes determined by the size of the loop coil buried in the roadway. The reality is that when ILD
sensitivity levels drift from their correct settings, the detection zone size changes. By using the correct
detection zone lengths, loop detector measurements can be corrected. This software-based approach is
proven effective and can be retroactively applied to archived data as well.
The loop error identification and correction algorithms have been implemented in the prototype
Datamart system, which is an online database system backed up by Microsoft SQL Server 2008 and the
Google Map technologies. It is highly scalable and has the potential to add new data sources from other
transportation agencies and online analysis functions for regional transportation planning, traffic
management, and analysis purposes.
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