The study of vehicle classification equipment with solutions to improve accuracy in Oklahoma.
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2014-12-01
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Abstract:The accuracy of vehicle counting and classification data is vital for appropriate future highway and road
design, including determining pavement characteristics, eliminating traffic jams, and improving safety.
Organizations relying on vehicle classifiers for data collection should be aware that systems can be
affected by hardware and sensor malfunction, as well as the equipment’s implementation of classification
scheme (i.e., algorithm). This report presents outcomes from an extensive statewide examination of
vehicle misclassification at Oklahoma Department of Transportation (ODOT) AVC stations employing
the PEEK Traffic ‘FHWA-USA’ classification algorithm. A ground truth system utilizing continuous
video recordings was developed and utilized. Results from the rigorous investigation are reported herein.
Also detailed in this report is a novel method for an improved classification algorithm designed to reduce
the number of classification errors. Thirteen Gaussian distributions were employed to model axle spacing
for each of the 13 FHWA vehicle types. Classifications obtained from video recordings and PEEK Traffic
axle spacing measurements for a sample of 20,000 vehicles were recorded and analyzed to obtain 13
good-fit Gaussian distributions that correspond with each vehicle class. An optimization algorithm was
then implemented to develop axle spacing thresholds for vehicles currently traveling Oklahoma’s
highways and to minimize vehicle misclassification. The new scheme was then implemented in the PEEK
Traffic automatic data record equipment and experimentally evaluated for accuracy. Results demonstrated
its effectiveness in improving vehicle classifications and reducing persistent overall system errors
characteristic of the ‘FHWA-USA’ Scheme. Analysis methodology detailed in this report will benefit
organizations interested in improving vehicle classification and overall system accuracy.
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