United States Department of Transportation
i
Calibration of automatic performance measures - speed and volume data : volume 1, evaluation of the accuracy of traffic volume counts collected by microwave sensors.
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2015-09-01
[PDF-2.21 MB]
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Abstract:Over the past few years, the Utah Department of Transportation (UDOT) has developed a system called the
Signal Performance Metrics System (SPMS) to evaluate the performance of signalized intersections. This system
currently provides data summaries for several performance measures including: 1) Purdue Coordination Diagram, 2)
Speed, 3) Approach Volume, 4) Purdue Phase Termination Charts, 5) Split Monitor, 6) Turning Movement Volume
Counts, 7) Arrivals on Red, and 8) Approach Delay. There is a need to know the accuracy of the data that are being
collected by the Wavetronix SmartSensor Matrix and displayed in the SPMS. The TAC members determined that
the following factors would affect the accuracy of radar-based traffic sensors the most: sensor position, number of
approach lanes, and volume level. The speed limit factor was added to the study after most of the data collection
was completed. The purpose of this research was to collect data at various intersections to determine the accuracy
of the data collected by the Wavetronix SmartSensor Matrix. A Mixed Model Analysis of Variance (ANOVA) was
employed to analyze the effects that each factor had on the accuracy of the traffic volume count. A total of 14 tests
were performed to examine the effects of the factors on traffic volume count accuracy. The sensor position factor
was not found to be a statistically significant factor affecting the accuracy of traffic volume counts. The effect of
speed limit on traffic volume count accuracy was determined to be inconclusive due to the lack of samples to be
tested. The remaining, volume level and number of approach lanes, were found to have a statistically significant
effect on the accuracy of traffic volume counts. Based on these two factors, a table of accuracy ranges was created
to meet the needs of UDOT to present accuracy ranges on the SPMS website. This table includes the mean, 95
percent confidence interval of the mean, standard deviation, number of samples, and the minimum number of
samples needed. In general the sensor provides accuracy level that is ready for practical use by traffic engineers.
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